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Alternating Current

Signaling

HAROLD McCREADY

thCtw York Office Manager
Union Switch & Signal Co,

TMDC

PUBLISHED BY
SWISSVALE. PA.

1915

Xttiott i^mitrli ^ l^tml (En.
Swissvale, Pa.

PITTSBURGH PRINTING COMPANY
PITTSBURGH. PA.

THE UNION SWITCH & SIGNAL'

APR 20 i32QcOMPANY

O OV Founded by George WestingkouM, 186

* 'V\ \^ OF PITTSBURGH, PA.

GENERAL OFFICE AND WORKS:

SWISSVALE, PA.
Floor Space: 550.254 Sq. Ft. Employees: 3.000.

Creators of the Alternating Current System of Sig-
naling and Owners of All Its Fundamental Patents.

Designers. Manufacturers and Erectors of All Kinds
of Signal Apparatus for Steam and Electric Railroads;
Owners of the Westinghouse System of Electro-
Pneumatic Block Signaling cmd Interlocking.

Electro-Pneumatic. Electric (A. C. or D. C), Ele&-
tro-Mechanical. and Mechanical Interlockings.

Automatic and Semi-Automatic Block Signal Sys-
tems Operating on Either Direct or Altcemating Cur-
rent; also Manually Operated Block Signals.

PLANS AND ESTIMATES ON APPLICATION.

DISTRICT OFFICES

Hudson Terminal Bldg. Peoples Gas Bldg.

NEW YORK CHICAGO

Railway Exchange Bldg.
ST. LOUIS

Canadian Eaq>ress Bldg. Candler Annex Pacific Bldg.

MONTREAL ATLANTA SAN FRANCISCO

Represented in Australasia, South Africa and Argentina by the

General Electric Co.

CONTENTS

Chapter P*f«

I Alternating Current Signaling^ — History and

Advantages 5t

I I Theory of Alternating Currents ... 29

III Elements of the A. C. Track Circuit . 63

IV Relays 79

V Electric Road Track Circuits ' . 141*

VI Transformers 171

VII Track Resistances and Impedances 219

VIII Signals

Part I — Semaphore 239

Partll— Ught . 286

IX Transmission Systems and Power House

Equipment .... 303

X Electric Interurban Road Signaling 349

XI Type "F" A. C. Electric Interlocking System. 365

XII Accessories for A. C. Signal Systems 417

XIII Track Circuit Cedculations .... 437

XIV Tables and Data 459

XV Index 537

CHAPTER I.

ALTER^rATING CURRENT SIGNALING.
History and Advantage*.

ALTERNATING CURRENT SIGNALING.

more, maintainers, familiar with direct current apparatus only,
are quite certain to be pretty much at sea at first when called
upon to care for an alternating current installation. It is the
purpose of this book to cover in as thorough and jret simple
a manner as possible the field of alternating current signaling
as applied both to steam and electric railroads.

HISTORICAL SKETCH.

I. Attempt to use Simple D.C. Track Relay on Electric
Roadf • 1 1 is a peculiar fact that, although to-day, for reasons
involving economy and dependability, the steam roads are
making the most extensive application of alternating current
signeding, the invention of the alternating current track cir-
cuit, which started the ball rolling, was first taken advantage
of by roads using direct current propulsion, and the original
installations were made on electrified lines. The idea, how-
ever, did not spring into existence Minerva-like at the first
call; it was the result of a graducJ evolution from the imper-
fect to the ideal.

The direct current track circuit, credit for whose invention
in 1872 is now generally conceded to William Robinson, of
Brooklyn, N. Y.. came into extensive use in the middle nine-
ties and had reached a high state of development in 1900 when
it first became necessary to signal the elevfited electric roads
whose operating conditions, as regards speed, frequency of
service, and weight of rolling stock, were in many ways com-
parable to those of steam roads. In view of the success of
direct current track circuits on steam roads, \t was only natural
that an attempt should be made to apply them to the roads
using electric propulsion. Right here some Isnags were struck.

As everyone knows, the running rails of electric roads are
used as a return for the propulsion current. The automatic
block signaling idea, however, involves a division of the track
into sections «each electrically insulated from the other, so
that one of the running rails had to be given up for signaling
purposes to act as a "block" rail, not a part of the propulsion
current return. In the case of the elevated roads, this was not
a serious matter as the elevated structure itself constituted a
propulsion return of many times the conductivity of the run-
ning rails. On the other hand, the sacrifice of one of the rails

HISTORICAL SKETCH.

on subway and surface lines was a serious handicap, as it
doubled the resistance of the return.

i®/t

^»^THIRD RAIL OR TROLLEY WIRE

BLOCK RAH.

9 I

Fig. I — D.C. Track Circuit Applied to an Electric Read

The difficulties encountered in the application of the direct
current track circuit to electric roads will be understood from
a study of Fig. 1 , where T represents the usucJ D. C. track
relay connected to the rails with a limiting resistance R in
series and fed from a track battery D. The main generator
for supplying power for propulsion purposes is shown at G.
Suppose, now, that a train at B has proceeded 1 000 feet in the
block, and that the propulsion current in the return rail flow-
ing towards the negative side of the generator is 200 amperes;
if the resistance of the return rail (1 00 lbs. per yard bonded to
capacity) is 0.0088 ohms per 1000 feet, there will be a differ^
ence of potential of 0.0088 x 200 = 1 .76 volts between A and
B. A moment's reflection will make it evident that «-!iis differ*
ence of potential is transmitted directly to track terminals A
and C of the relay T, because the resistance of the cetf axles
and the block rail between C and B is negligible; in other
words, the axles and the block rail form a low resistance con-
nection between points C and B so that there is a ditference of
potential of 1.76 volts between A and C. If, say, a 16 ohm
track relay, picking up at 0.5 volts were alone used, the signal
would be clear with a train in the block due to the relay being
picked up by the drop in the propulsion rail. To eliminate
this difficulty. Series resistance R is inserted in the reliiy cir-^
cuit to reduce the maximum propulsion drop across the relay
coil terminals to a figure well below the pick-up point — say 50
per cent, to allow a safe margin. For example, if the maxi-
mum propulsion drop across the rails opposite the relay is 1 .76
Yolts during rush hours when all trains are running, and it is

10 ALTERNATING CURRENT SIGNALING.

to be reduced to 0.25 volts across the terminals of a 16 ohm
relay, a resistance R of zr-zz x 16 = 96.6 ohms, must

be used; of course, the same relay wound to a high resistance
might be used instead with no external resistance, but the use
of the external resistance would be advisable because of the
possibility of adjustment in case of an increase in the propul-
sion drop resulting from heavier traffic

With an accurate knowledge of the maximum propulsion
drop and adequate provision in the way of resistance to pre-
vent the track relay being falsely energized, a system con-
structed on the above lines would be satisfactory provided
the bonding of the return rail is well maintained. It will be
seen, however, that a defective bond in the return would cause
a rise in the return resistance with a corresponding increase in
the propulsion drop across the relay; with a broken bond, this
increase might actually cause the relay to pick up with a train
in the block. Serious results might also occur in the event of
imperfect contact between the return rail and the car wheels,
for then the block rail would be in the direct path of the re-
turn. This would subject the track relay tb practically full
|>r6pulsion potential with obvious results.

2. Special Polarized D. C. Track Relay Designed lo.r
Boston Elevated. The limitations of such a system were,
therefore, considerable. It was felt that some better plan was
required, and the first step in this direction was the polariza-
tion of the track relay against the etfect of propulsion drop.
The first installation involving this safety feature was made
on the Boston Elevated in 1901. 7*his practically marks the
beginning of automatic signaling on electrified roads. Track
circuits for about 1 73 one-arm semaphore signals were put in,
the signals themselves being electro-pneumatic Owing to
the great capacity of the elevated structure as a return con-
ductor, only a small fraction of the propulsion current flowed
through the return rcul. This, together with the fact that fre-
quent train service of the elevated rendered short block sec-
tions imperative, resulted in a comparatively small propulsion
drop per tract circuit, normally well below the pick-up point
of the relay.

The Boston Elevated track circuit is covered by Fig. 2;

HISTORICAL SKETCH.

where it will be noted that the positive side of the power gen-
erator G at the right of the diagram is connected to the third
rail and the negative side to the return rail and the structure'
as usual, whereas the positive side of the signal generator L is
connected to the return rail, and the negative side to the signal
main feeding the track circuits through ft resistance.

'SIQNALMAIN

Fig. 2 — Boston Elevated Tnck Circuit

The polarized track relay shown at the right in Fig. 2 con*
sists of a horse shoe electro-magnet energized by two coils SS
just as in the case of the well known direct current track relay
used in modem steam road service. The armature at the bot-
tom of this magnet is pivoted at its right hand end. so that
when coils SS are energized from the track this neutral arma-
ture lifts the vertical rod at the left of the coils and actuates
the horizontal contact bar at the top of the relay. This con-
tact bar, made of a flexible metal strip provided with a carbon
contact block at either end, is carried by, but insulated from
the polarized magnet P pivoted at the top of the horse shoe
magnet and swinging between its coils. When the block is
clear, as shown in Fig. 2, magnets SS are energized, and the
neutral armature lifts the vertical rod at its left end, so that
the left hand contact on the horizontal contact bar is made,
thus energizing the swinging polar magnet P from the signal
main.

It will be seen that the horizontal contact bar at the top of
the relay is under the joint control of the neutrcJ and polar
armatures, so that, if coils SS are energized by current flowing
in the proper direction, the lower pole of P will be attracted t

12 ALTERNATING CURRENT SIGNALING.

' '

€>
the right; then the contact. on the right of the horizontal bar
.will be made to close the signal control circuit. Cpil^ S5 and
P are connected so that when no train is in the block, current
will flow from the positive side of the signal generator, from
left to right along the return rail and through coils SS to
swing magnet P to the right to close the signal circuit; on
the other hand it is to be noted that with the 500 volt -main
power generator located and connected as shown, propulsion
drop in the return rail will tend to send a current across the
car axles and from left to right along the block rail, to track
coils SS of the relay in opposition to the signaling current.

Thus, whereas the signaling current is of such polarity as to
excite coils SS so as to swing magnet P to the right to close the
signal circuit, the propulsion current flowd in the opposite di-
rection so as to reverse the polarity of coils SS and thus swing
magnet P to the left to open the signal circuit and throw the
semaphore to danger. Ordinarily, the propulsion drop in the
return rail on the Boston Elevated was too small to cause the
relay to thus open and delay trafHc; in case of sudden unex-
pected increases in the propulsion drop, however, due to rush
hour traffic, poor bonding of the return, or to a poor contact
between the car wheels and the return rail, the polarized fea*
ture became effective to prevent the signed g^iving a false
clear indication.

3. Limitations of Boston Elevated Polarized Relay.

Certainly the Boston EUevated track circuit as above dc
scribed was of undoubted merit and the best in the field at
the time it was installed. It was later found, however, that
its advantages were somewhat limited because the direction
of the propulsion drop was not always constant, due to shift-
ing of the load between the three p>ower houses along the
right of way. Sometimes most of the return current would
flow towards one power house and then again in the opposite
direction to another power house, depending on the location
and density of traffic at that particular time. For this reason
a relay was later placed at each end of the track section in
many cases so that at least one relay would be always shunted
with a train in the block, the signal control circuit, of course,
being broken through the contacts of both relays in series.
While, naturally, this precaution tended to lessen greatly the

HISTORICAL SKETCH. 13

possibility of false indications, absolute safety is secured only
through a rigid maintenance of the bonding of the return.
Therefore, whereas a system of this type, well inst^ed and
maintained, possesses points of merit, it is not ideal in that
it is not free from the interference of propulsion drop, the
block must be comparatively short if this propulsion drop is
to be kept down, and one rail has to be given up for signaling
purposes; this latter may be a serious matter in the case of
surface lines and subways where there is no structure to serve
as a return. However, the Boston Elevated signal system
has given p>erfect service for almost fifteen years now; not a
little of the credit for this is due to excellent maintenance en-
forced by a very able and energetic signal department.

4. Invention of the A. C. Track Circuit. A consid-
eration of the foregoing discussion will make it evident that
the successful solution of the track circuit problem on electri-
fied roads yet remained to be found. A brand new idea was
wanted — ^some means of rendering the track circuit absolutely
immune to the effects of propulsion current. It remained for
Mr. J. B. Struble, an engineer in the employ of the Union
Switch & Signal Company, to solve the difficulty once for all.
He had been prominent in the Boston Elevated development,
bu^ had previously conceived the simple yet rare idea of a
true selective relay — one designed to respond to an alternating
signaling current, but to be absolutely free from the possibility
of closing its contacts no matter how much direct current
passed through its energizing coils. This involved a motor
device, the so-called Vane Relay, working on the induction
principle, which will be fully described in Chapter IV.

The first extensive trial of Mr: Stt-lible's invention was made
in !%3 between Sausalito and San Anselmo, oh tke North
Shore lUiilroad in California. The situation was in a way
novel in that the road was originally built for narrow gauge
stecun service; later, a standard gauge electric service was
added over the same p>ermanent way through the addition of
another rail. The rail common to both gauges was used as
la block rail, so that the remaining two rails constituted a re-
turn for the propulsion current — 500 volts D. C. Thus, trains
of either gauge would operate the signals. The system con-
sisted of thirty style "B" motor signals, covering ten miles of

U ALTERNATING CURRENT 5ICNALIMC.

double track, operated by etoraee betterie* through an alter-
neting current track circuit contnJ.

The track circuit conductor system empl<^^ waa, there-
fore, much like that of the Boatcn Elevated previously de-
scribed, excepting for the presence of two return rails. To
feed the track circuits, two wires carrying alternating current
at 2300 volts. 60 cycles, were strung on a pole line along the
right erf way and a step-down transformer located at the exit
end of eaiJi track circuit supplied current at a low voltage to
the track for the operation
of the selective alternating
current track relay.contnd'
ling the signal at the en-
trance of the block. Some
of the track circuits were
about a mile long. and. a
copious rains are frequent
in that district during the
wet season, the system was
^ven s severe test. The
ballast was cf gravel artd
well removed from con tact
with the rails. Under the
worst conditicms the relays
operated with a margin of
from 30 to 40 per cent
above the failing point-
The system was a success
in every way.

5. A. C. Track CircuSta Installed on New Yo»-k Sub-
way. About this time the question of signaling the New
York Subway came up for settlement. There were about 70
track miles, two, three and four track, to be signaled, the pro-
pulsion system being 500 volts D. C The traffic rai thislineis
undoubtedly the heaviest in America; for example. 2,068 trains
pass Ninety-Sxth street every 24 hours,, these trains consist'
ing of 10 cars during the morning and evcnmg rush- It was
decided to install electro-pneumatic signals controlled by A. C>

HISTORICAL SKETOi. ^

traick circuitB. The system comprises some 500 track circuit*.
700 (igDali^ and 40 electro-pneumatic interlockinss, and is oaa
of the three or foiu greatest installations in the country.

Single roil track circuits, similar to those of the North Shore
were installed with Vane type A. C. track relays fed along the
rails from tiansfonners located at the leaving end of each
block and atepping down from the 550 volt. 60 cycle, signal
mains to 10 volts for the track. Fig. 3 shows one of the in-

strument cases suspended on a column near a signal. The
tiansformer feeding sigluJing current to the track is shown at
the top of the column. Just below it in the instrument case
will be seea two resistance grids, one of which is placed in the
track leads of the transformer and the other in the track leads
of the A. C. track relay immediately below the grids. 'These
gtids prevent exceasive heating of the transformer and relay
due to the flow of propulsion current resulting from direct cur-
rant dn^in the return rail. The relay is still further protected

16 ALTERNATING CURRENT SlONALlNC.

by an impedance coil shown at the bottom of the instniment
case; this coil shunts out direct current from the relay, as will
be explained in Chapter V.

Because of the density of traffic, the blocks had to be nude
a* short as consistent with safety; the average block length ia
about 620 feet, this distance being one and one-half t'mes the
full speed braking distance. Altogether the conditions were
extraordinarily severe, but the signal system has met the re-
quirements niagniflcently, having a record of one failure of
apparatus to 3,359.167 movements. The line carries over
1,000,000 passengers a day and never has a passenger been

m Huvy Ehclric Trunk Liw

killed through any fault oF the signal system; as a matter fact
only one passenger has been killed in the entire history of the
road and this was due to panic in a train resulting from a blow
out in a high tension power cable. This temarkable perform-
ance has made the New York Subway system one of the
classics of the ugnal world.

6. Invention of the Impedance Bond. Other installa-
tions <A single rail track circuits, notably that of the Phila-
delphia Rajud Transit in 1907. weie made, but the fact that

HISTORICAL SKETCH. |7

one of the propulsion nula had to be given up hx BignaKng was
a aerioua limic&tiDn on aurface roads where the large cmduc-
dvity of a Btriicture was abaent. This objection Was finally
removed, through the invention of a practical balanced im-
pcdance bond and its application to the so-called double roil
track circuit by Mr. L. H. Thullen. then Electrical Engineer
of the Union Switch Ct Signal Company; Messrs- Young and
Townsend, of the General Railway Signal Company (then the
Ta^or Sgnal Company), were also cmmected with this de-
velopment. Mr. Thullen's scheme included the use of an

Fii.6. ACoinsrsltlBCiHt Pmiii]4Twua TuniiiiKl, New YackCity

A. C. track relay fed trom k transformer over the rails a* usualj
but the track circuit was com|^tdy iscJated, insulatioti joint*
being placed at the ends of the block in both running rails.
The novel feature of the invention was that the passage
of the return propulsim current back to the power bouse
was provided for by the use of balanced impedance bonds con-
nected across the rails at the ends of the blocks; these binds
offer impedance to the passage of the alternating signaling
current, but they are previded with a baavy copper wiiKUng

18 ALTERNATrNC CURRE^^T SIGNALING.

(xmnocted to a« to offer nesligible resi*taiic« to the flow of the
direct propuluon current from track circuit to track ciront.

The first installatiMt'Of <}oukIe nul tnck circuits with im*
pedance bonds was made on the Uses o( the Boston Ellevated,
where, in 1904-5, shout fourteen track circuits of this type
were put in on the East BostMt Tunoel under the Boston Har-
bar. On the basis of the satiafactory results there obtained, a
much larger system was installed on the electrified linee of the
Long Island Railroad in 1906, where 1 40 track circuits vicre
used <m 1 9 mileaof double track, and 4.5 miles of four-track road,
the propulsion being 500 volts D. C. with 1 1 00 amperes return
current per rail. The Long Island job was followed by an

the same year on
the West Jersey S<
Seashore Railroad,
where 1 20 block sec-
tion a, of an average
length of 4000 feet,
were installed on
thirty miles of
double track be-
tween Camden and
Newfidd, N. J., tm
the way to Atlantic
City. This ptopul-
I system was the
leas that of the
' Long Island, only the return current amounted to 1750 am-
peres per rail. Very important track circuit system* of the
same type have been installed on the Hudson & Manhattan
(1909) in the Nw York Central Electric Zone and the Grand
Central Terminal. New York. (1906-1910). at the Great
Pennsylvania Terminal. New York (1910— See Figure 6). and
lalsr on the electrified lines of the Southern Pacific in the San
Francisco district, where ex tensive developments, which would
surprise the Elaatemer, have been made. Many other large
•ystenu. too numerous to mention, have since been installed
lie double rail track circuit with impedance bonds is now th«
•ndaid for long track circuits on electric roads.

ctrkZonc, Aluneda

HISTORICAL SKETCH. 19

7. Where Frequency Relays Were First Used. All tin
above roads were characterized by D. C. propuluon, but in
1906 when certain portions of the New York, New Haven Ac
Hartford w^e electriliixl for 1 1 ,000 volt, 25 cyde A. C. pro-

pulaicHi. it became necessary to devise a tracL relay whuJi
would not respond to either D. C. or 25 cycle A. C. propul'
tioD currents foreign direct current had to be guarded against,
because t^ the proxiniity tJ D. C. propulsion roads. The dif-
ficulty was successfully met by the invendon of what is known

OS the frequency relay, in this case an A. C. track relay which
will not respond to the low frequency 25 cycle propulsion cur-
rent, but will work on a higher frequency, say 60 cycle, ugnal-
ing current; the selective principle is thus again utilized.
Messrs. Howard and Taylor, of the Union Switch fie Signal
Company, are to be credited with the invention of successful
relays of this type. The New Haven installation embodied
th* use of frequeocy relays .on double rail track ci

ALTERNATING CURRENT SICNALINC.

impedanc« bond*, which latter atiU muntain tKe (xmtinuityof
the propuluon return whjle choking back the flow of si
current, aa explained in Chapter V. The rapid e
A. C. propulsicm on the New Haven has brought thia ayatem
into great prominence. The New Haven ia remarkably pro-
greaiivD in an engineering way and ia now operating both
pasaenger and freight trains electrically on it* four and lix
track main line between New York and N«w Hav«n, a dis-
tance of 75 miles.

Other extenaive installationa on roads uaing A. C. propul-
sion have since been made on (he New York, Westchester and
Boston (1911). ■ heavy suburban road, running north from
New York to White Plaina and east to New ftochelle; in 1915
on the main
line of the
Pennsylvania
Railroad, run-
ning west from
Broad Street
Station. Phila-
delphia, to
Paoli, where
all suburban
traffic is hand-
led by multiple

Fi(. 9. Siyb "B" Siflub oa ibc St. Pnul and also in

1915. on the

Norfolk and Western, where a long ttretch of the main line

in the West Virginia mountain district has been electrified

to handle heavy coal trains.

8. SteamRaadaA<]apttheA.C.SyaUm. Theuntvenal
success of A. C. sigrtaling on electric roads, together with ad-
vantages in the way of safety and econmny. brought about the
adoption of the some system on steam roads. The first in-
stallation of this kind was made on the Union Pacific Railroad
near Council Blufis, la., in 1906, where 16 track circuit* were
put in. This was shortly after followed by a number of small
installations oa the Pennsylvania Railroad, wheie foreign cur-
rent interfered with the pr^ier opaiatiaD of I>. C track cir-

HlflXMtlCAL SKETCH. 2r

cuits. The Pennsylvania later adopted A. C. dtnaling as a
standard (or all new blocking, and now, with the exception <rf
certain relatively short itretches, the entire main line between
New York. Philadelphia, Baltimore, Washington and Pitts-
burgh is protected by a. c. automatic blocksignals. Other great
roads, particulariy the Santa Fe, the Chicago, Milwaukee &
St. Paul, the Norfolk and Westtm and the Southern Podiic,
have mads importaltt installations; the St. Paul alone has
equipped tOOO track mile* of the main line with alternating

S. Signaling Begins onthclnterurbanElectricRoMla.

The latest developments in the alternating current ugnaling
fidd have been
made tm the
high speed
dectric intef
urban roods,
where the ser- .,
vice is in many
ways similar to
that ot steam
roads, es-
pecially a* re-
gards speed,
frequency of

weight of Tol- ■ Fig. 10. T-2 SigMl. on P. R. R.

ling stock.:

Much special jipparatus, and many novel control si
have had to be devised to meet the requirements of single
track operatioiii characterizing moat of the trolley roads.
IHg. 12 iUiutrates an interurban car on the Indianapolis,
Columbu* & Southern wailing on a stub siding for an
^posing car to.pass on the main, the semaphore signals
being cleared f^r a movement in either direction. The first
of a large number of extensive signal installations on the
■n^enirban roods was made on the Illinois Traction System in
1910, 100 miles ot single track being signaled. Automatic
dectrie block tigdhls contnJled by continuous a. c. track cir-
cuits are now considered the standard for the protection

a ALTERNATING* CURRENT SIGNAUNC.

high speed interurbun fouIr, trolley contacts and similar de-
vices not being entirely dependable (or speeds over 30 miles
per btnir.

10. Advent of the Light Signal. Along with the new
ugnnling <m the intenirban roads hat come the Light Signal,
used for both day and night indication: on single track cross
country electric lines, the signal must'oFten show up against f
forest of vertical lines constituted by'the pole line and trolley
supports, so that in Aisny coses a color indication will con-
trost better with such a background than the posidon indi-
cation of a semaphore blade. The ordinary three position
c<Jor light signal (Fig. 13) consists of a combination of colored
lenses varying

from 5ji" t*
10" Illumi-
nated by -in-
candescent
lamps (red for
"slop", yellow
for ■■fflution".
oikd green for
"proceed"),
the tenses be-
ing shielded
ogainat sun-
Ht.l1. Style -S" Si(ub on Ike Sutk Fa lightbyadeep

overhanging
hood. Depending on the sixa of the lenses and the candle
power of the lamps back of them.such signals can ordinarily
be seen from ZSOOMDOO' on a tangent, under favorable
weather conditions, and from 1500'-2500' at those hours of
the day when the sun shines directly on the lenses. Due to
its freedom from moving mechanical parts and ganoral sim-
plicity, the light signal is receiving serious consideration
even by the signal enginoers on the heavy trunk lines, an
initial installation of color light signals having been made
only « few months ago by the New York, New Haven Gt
Hartford. Tlie latest development in the light signal field is
the "position" or "beam" light signal (Fig. 14). consisting, in

HISTORICAL SKETCH. IS

the case of a three poduan signal of three rows of uncolored
lense* with their incandescent lamps arranged in three radial
lines projecting horizontally, diagonally «t 45°, and vertically
from the central point of diventence; the illumination of the
bottom, or horizontal, row of lights indicates Stop, that of
thediagODat, «r 45° row Caution, and that of the vertical
row. Proceed, the control being easily effected over the
points of a three position relay. This scheme is the joint

invention of Mr. A. H. Rudd, Signal Engineer <d the
Pennsylvania Railroad, and Dr. Wiltiam Churchill, of the
Coming Glass Works.

ADVANTAGES OF A. C. SIGNALING.

It will be fairly evident from a consideration of the discua-
NOn at the beginning of this article that the alternating cur-
rent system is the only really satisfactory method of signaling

24 ALTERNATING CURRENT SIGNALINC.

dectric road*. What are it« recommendatioiu for ateniii
roada? The {ollowing aummary of the advantages offered by
'be alternating current «ystem will aupply the snawer.

1. Safety.

(a) A. C. apparatus, working on the induction prin-
ciple, is inunune to the dangerous effects of direct current.
The necessity fen- such immunity is imperative in t^e
case of track relays on electric roada using direct cuireiii
propulsion. Where
altematinK current
propulsion is used,
the relays may be
designed to respond
only to a certain
frequency, much
higher than that of
the propulsion sys-
tem; in this case
the track relay is
again perfectly se-
lective. On steam
roads, foreign cur-
rent troubles have
greatly increased,
due to widespread

urban trolley lines
during the past
few years. With
alternating current
track relays, such
troubles disappear.

(b) Residual magnetism troubles arc eliminated through
the use of altemHting curretit apparatus working on the induc-
tion principle. This is of great importance in the case of rC'
lays, holding devices, etc.

(c) Due to the fact that large amounts of electric energy
are available, A. C. appars^tus may be designed with good
mechanical clearance* and thus have a large safety factor.

HISTORICAL SKETCH. «

(d) Complete protection against broken down insulation
jconts. which might otherwise cause false clear failures, can be
secured through the use of two element altematiiig current

2. Economy.

{a) The maintenance charge on A. C, systems is much
less than that for D. C. systems. Track and line batteries
are dispensed with and the signals arc lighted by electric
lamps fed from the signal mains; battery men and lamp

Fig. 14. Poaitiaii Li|ht Siiiula, P. R. R,

lata are not required. In many cases one man is main-
taining thirty miles of track and he spends his time on the
signals, not in cleaning batteries. Often he looks after one or
two small interlocking plants in the bargain.

(b) A. C, power can naturally be produced more cheaply
than D. C. power by batteries. Elstimates* of the cost of

ALTEAMaTING current SICNALINa

power delivered by batteriei^. ivary from $5.00 per kilo-watt

hour for primary batteries to $14.71 per kilo-watt hour for

storage cells chat'ged by gravity batteries. The average cost

of A. C. power is abdlUt 2.3^ per kilo-watt hour; it will vary

from 1 4 per kilo-watt hour to 1 0<f per|kilo-watt hour, depending

on the location ahd the amount of power used.

\ ■ i
3. Simplicity.

(a) Track circuits up to 25,000 feet in length are being
successfully operated by alternating current. Cut sections
with their relays, housing and ' other complications are
diminated. Cases kave occurred bri important stretches
of track, where, due to abnormally poor ballast condi-
tions. D. C. track circuits proved iiSiphicticable. This situ-
uation was met by the Use of the A. C. system, because it was
a simple matter to supply enough power\o compensate for the
track losses and wotv the relays. In fact the length of the
track circuit in the A. C. system is limited in most cases only
by the length of the blodk, that is, the perhiissible distance be-
tween succeeding sigiadU, as dictated by: iHe density of traffic.
This makes for simplicity.

(b) The mere fact that there are nc^i-, batteries reduces the
complication of the A. C. system; their place is taken by trans-
formers which require no attention.

4. Dependability.

(a) The power supply for A. C. systems is contin-
uous as long as the power house and transmission
are in commission; experience has shown that interrup-
tions may easily be guarded against by constructing the
transmission line iit a substantial manner Und by providing
duplicate generating Apparatus in the power house. Direct
current systems occasionally fail because of thi6 freezing of the
batteries in cold \i^ther; cracks sometimes appear in the jars,
and the liquid leaks Out; or perhaps local actkm in the cell
gradually "kills" it. Such interruptions in the current supply
throw the signal to dailger and delay traffic. A. C. systems
are free from this.

(b) PracHcally constant voltage characterizes the A. C.
system, whereas thd voltage on D. C. systems, not only falls

HISTORICAL SKETCH. 27

gradually as the batteries become older, but drops otf sudden-
ly as they approach exhaustion. This means that where A. C.
is used th# signals always clear in the same time, and the track
relays never fail to pick-up due to an exhausted track battery.

(c) A comparatively high voltage ( 1 1 0-220) is used in A. C.
signaling for operating the signal motors. The voltage drop
in relay contacts is, therefore, insignificant; contact resistance
is of no importance.

(d) Induction motors are generally used for operating
A. C. signals. These motors have no commutators or brushes
of any kifld. Coukmutator troubles disappear.

5. C>ther Advantages*

(a) 'the installation of an A. C. system on a steam road
may be made to anticipate the future electrification of the
line aiid provide for it.

(b) Tlie A. C.^ mains feeding the signals, track circuits*
etc., may be used to supply power along the right of way for
other pufposes besides signaling — station lighting, for ex-
ample.

Many extravagant claims have been made for alternating
currmt signaling, most of which, happily, it has been able to
meet. It is only fair to state, however, that there are certain
sectionif df the country where the cost of power is relatively
high and where, consequendy, an alternating current signal
systenk might not be as economical as a direct current installa-
tion with batteries; such cases are rare and are gradually dis-
appearitkg as the country develops and commercial power be-
comes more and more available. Furthermore, the initial
cost of an A. C. system will, in most cases, be greater than
that of ah equivalent D. C. system, but this is generally more
than cdftlpensated for by the saving in maintenance and
power, so that the alternating current system pajrs for itself
in a Iddgfier or shorter time, depending on local conditions, and
th^e is thereafter a constant saving.

^Neither ought the alternating current system be considered
as a paiiacea for all troubles met with in signal practice, for
A. C. relays, signals, etc.» require proper maintenance, just

ZS ALTERNATING CURRENT SIGNALING.

..■»!' ■■-■■■'' ■■

like all other types of signal apparatus. It must also be re-
membered that new principles and ideas have had to be used
in the design of A. C. apparatus, and it is only natural that new
problems, having no parallel in direct current work, have re-
sulted. Forty years have been required to bring the D.C. track
relay to its present simplicity, and time and experience are
bringing alternating current signaling to the same high state
of simplicity and perfection.

CHAPTER II.

FUNDAMENTAL THEORY OF
ALTERNATING CURRENTS

CHAPTER II.

FUNDAMENTAL THEQRY OF
ALTERNATING CURRENTS.

Before proceeding with the study of the design and oper-
aticm of alternating current signaling apparatus, it is desirable
to possess a working knowledge of the ph|r8ic8 and mathe-
matics of alternating currents. Unfortunately, there seems
to be a general impression that this subjjfB^t is a bit too abstruse
for anyone not a mathematician or a college graduate. Nat-
urally, the designing engineer must have a^ thorough and de-
tailed knowledge of physics, mathematics and electricity; in
addition, he must have a broad practicij experience before his
theoretical training will be of much value, fqr there are many
pitfalls not mentioned in the text books. Most of the funda-
mental facts, however, are within the grasp of almost every-
one, and this chapter will, therefore, be devoted to a presmta-
don of such alternating current theory as will enable the sig-
nalnuM\ ^^ understand the most important factors entering
into ti|Ci workings of A. C. apparatus.

GlINERATION AND CHARACTERISTICS OF
ALTERNATING CURRENT WAVES.

1. Simple Alternator. A generator which produces al-
ternating current is known as an alternator. Alternators gen-
erate currents on exactly the same principle as direct current
djniamos, and in fact, the two types of machines are alike in
all important respects, with the exception thi||t, whereas the
direct current ■ machine is provided with a coi^^mutator to
maintain the direction of current constantiii- the atemal cir-
cuit, the alternator supplies current to t^ctextemal cir-
cuit just as it is generated without rectificatiQJii^^.of direction.
Currents are, therefore, said to be direct or alternating in char-
acter, depending on whether they flow alwfiys in one direction
with a steady value, or whether their direction and strength
vary periodically.

A simple form of alternator is shown in Figure 1 5, where N
and S are the poles of a field magnet, which latter, in some
cases, may be a permanent magnet, as for example, in tele-

ALTERNATING CURRENT SIGNALING.

Fig. 1 5. Simple Bi'PoIar Alternator
No- Voltage Position

phone or automobile xnEignetos. but is alvsrays a large electro-
magnet, excited from some direct current source, in the case of
power generators; the point to be remembered is that the field

magnet is of con-

stant polarity.
Rotating on a hor-
izontal axis in the
magnetic field
whose flux lines
pass from N to S
as indicated by
the arrows, is a
loop of wire ter-
minating in two
metallic rings, R
and T, carried on, but insulated from, the same shaft
which drives the wire loop. R and T are known as slip
rings, and brushes A and B bearing on them, conduct the
current generated in the loop away to the external circuit
to which electric power is to be delivered. It is understood
of course, that the alternator shaft carrying the wire loop is
provided with a pulley to be driven r<cm an engine or some
other source of mechanical power.

2. Voltage Generated by Simple Alternator. It is a
fundamental fact that when a wire is forcibly moved across a
magnetic field so as to cut the lines of magnetic flux, an electro-
motive force is generated in the moving conductor. The
electro-motive force so generated is proportional to the
strength of the magnetic field and the sp>eed at which the con-
ductor is moved: or more simply, the voltage vsoies with the
rate at which the lines are cut. When a conductor cuts 1 00.-
000,000 flux lines in one second, one volt is generated in that
conductor.' Of course, when the rotating wire loop consists
of many turns, the total voltage generated in the coil is the
voltage generated in one conductor, multiplied by the number
of conductors moving in the magnetic field, for the conductors
comprising the coil may be considered as a number of batteries
connected in series. In the case of the 2-pole alternator
shown in Fig. 15, the voltage generated is:

2n^Z

i
t

100,000,000

THEORY OF ALTERNATING CURRENTS^ JS

Whoe E is the volteffe maom dip linss R and T. and n is ti»e

speed in levolutiaos par second at vdiidi tke loop, caanaistins

of a total of Z condncton (sodi as U and L). is htsDg moved

inafiddof ^linesof magnf tir foroe streamins from poleN

to pole S: the Gredc letter #. (pranoonoed "phT) is muvcr-

sally used in dectzical nlmlations to represent die total

number of flux fines oonstitnting the magnetic 6eld. The

factor 2 n in the above formida. representing the speed in

half revolutions per swond, is introduced because it is duiing

a half revolution that each conductor cuU a total of # lines.

If. therefore, the shaft of the simple altnnabMr shown in

Fis. 15 is revolving at a constant speed of 50 revolutions

per second and there are a total of tvro (2) conductors (one on

either side of the loop) cutting a magnetic fidd of 1.000.000

flux lines, then the electromotive force generated will be two

volts. Equation (I) above serves as die basis for the design
of all generatcws. large and small.

3. ^lape of Generated Wave. It will now be of interest
to investigate the form of the electrcHnotive force wave gen-
erated by an altematcw such as that shown in Fig. 15. which,
by the way. may be considered as representative of commer-
cial machines, for purpose <rf analysis and calculation. Keep-
ingin mind the fact that the electromotive force generated at
any point in the revoludcm c^ the loop depends on the rate at
which the lines of magnetic flux are being cut. it will be seen
that when the loop is exacdy vertical, as shown in Fig. 15. both
die upper conductor U and the lower one L, merely slide along
die magnetic lines for an instant without actually cutting
through them, under which circumstances, of course, no volt-
age is generated in either conductor. However, the moment
after the loop leaves the veitical position it begins to cut the
flux lines at,a low rate for the first few degrees of the revolu-
tion, because the movement of the conductor is more hori-
zontal than vertical; in other words, the action is still a sliding
one. rather than a cutting acdon. As the loop progresses in
its revolution, the cutting acdon becomes more and more
marked, until the loop is horizontal, as shown in Fig. 16, when
the conductors are moving at right angles to the flux lines and
the rate of cutting is the greatest; consequendy, the highest
voltage is generated when the loop is swinging through the
horizontal position. Naturally, as the conductors leave this

ALTERNATING CURRENT SIGNALING.

Fig. 1 6. Simple Bi-Polar Alternator,
FuII-Voltage Position

horizontal position, the rate of cutting the lines falls off sigain
and finally, when the loop is again vertical, but up'side down»
the conductors are once more sliding along the lines and no
voltage is generated. It will thus be evident that, during
each full revolution of the loop, the generated voltage falls
to zero twice and twice reaches a maximum.

Inaddition to the changes in the i^/ue of the generated electro-
motive force, there are also changes in its direction, which
must be considered. If the loop in Figs. 1 5 and 1 6 is revolving

in the opposite

direction t o
the hands of a
clock; then
conductor U
will be cutting
the flux lines
in a downward
direction and
conductor L
will be cutting
them in an up-
ward direction during the first half of the revolution; this
action is, of course, reversed during the second-half of the
stroke, for then, after the loop has been turned upside down,
conductor U is moving upward and conductor L is moving
downward. Now, it is an experimental fact that the direc-
tion of the voltage generated in a conductor moving in a
magnetic field depends upon the direction in which the con-
ductor is moving with respect to the flux lines, and no
better way of representing the relative directions of
flux lines, movement of the conductor and resultant
generated voltage exists thein that offered by a simple
law known as "Fleming's Right Hand Rule,'* illustrated in
Fig. 1 7, where the forefinger Y of the right hand indicates the
direction of the flux lines, the thumb X shows the direction in
which the conductor is moving in the magnetic field, and the
middle finger Z, bent at right angles to both thumb and fore-
finger, points in the direction in which the voltage is being
generated. Applying this rule to Figs. 13 and 16, it will be
seen that during the first half of the revolution the voltage
generated in conductor U tends to send a current from back

THEORY OF ALTERNATING CURB04TS. SJ

to front of that conductor and from front to back in conductor
L BB the latter is cutting the flux lines in the ^ipOMte direc-
tion, the direction of the flux linci, of course, remaining the
•ame at all times as previously stated. On the other hand,
during the second half of the stroke when conductor U i« mov-
ing upward, the voltage generated in U tends to send ■ current
from front to back, while in conductor L the opposite is tha
case. Itisalsoworthyof note that, due to the fact that con-
ductor U and L are connected in series, the voltage gener-
ated in one of them tends to send
a current around the loop so as
to help the voltage generated in
the other conductor; hence, the
voltage across slip rings R and
T is double that generated in
one conductor. To sum up.
therefore, the voltage generated
in such an alternator rises in
one direction from zero to a
maximum, falls oif again to zero,
then rises in the opposite direc'

tion to a maximum and falls once more to zero. Mice
during each revolution of the alternator shaft.

The above discusBion covers only the nature of the changes
in the direction of the generated electromotive power without
reference to magnitude. The successive changes in the mag-
nitude and direction of the voltage generated during one revo-
liition of the loop shown in Fig. 15 is graphically illustrated in
Fig. 1 8. where the line OP. revolving counter-clockwise about
point O, represents to scale the maximum voltage generated
by the loop (the electromotive force generated when the loop
is in the horizontal position in Fig. 16). and the various angu-
lar positions of the line OP correspond to similar pbaidons of
the loop during its revolution. It is now proposed to repre-
sent, in pictorial fashion, the rise and fall in voltage during one
revolution of the loop, and for this purpose the circle in which
point P swings is divided in twelve parts, Pi. Pa. Pa— Ph-
Then a horizontal line at the right of the circle is divided also
into twelve equal parts: the line may be drawn to any length,
as that is merely a matter of scale. The point to be grasped
is that these horizontal positions mark the passage of time aa

M ALTERNATING CURRENT SIGNALING.

d\e loop swing* through the corresponding angles.

Now; the voltage generated st any point in the revolution

of the loop is proportional to die projection of lino OP at

Fis. IB. Sine Wav« DevetiipDHnt

that point against the vertical line AB, that is. perpendiculars
dropped from points P]. P^. P^. etc.. against AB. represent the
voltages generated in the loop at those positions: this results
from the fact that the number of hnes of force being cut at
any givon instant are diresctly proportional to the correspond-
irtg projection of the swinging vector OP on the vertical axis
AB. To plot the electromotive force wave generated in the
loop as the latter swings through one complete revolution, it
is, therefore, only necessary to project points P], Pj. P3, etc.,
horizontally to the right until they meet their corresponding
time verticals. Beginning at position Pi, which represents
the vertical position of the loop as shown in Fig. 1 5, no voltage
is being generated, as previously described ; the time is zero,
wnce the loop is just on the point of starting its revolution.
and, when Pi is projected horizontally to the right, it coincides
with point 1, indicating zero voltage at that time. As the
loop continues its revolution, the voltage increases until at P^ ,
when the loop has turned through 90" and occupies the hori-
zontal position shown in Fig. 16, the maximum voltage is
being generated and the projection of the line O P4 is equal to
the length of the line itself. Then, as the loop swings down-
ward, the voltage begins to fall off, until at point P;, when the
loop is upside down, the voltage is zero. Here the loop
egins to generate voltage in the opposite direction and the

THEORY OF ALTERNATING CURRENTS. 37

projection of Pg is below the horizontal line; the voltage once
more rises to its maximum and passes through the same set of
values as before, only in the opposite direction, and finally the
zero position is again reached and the loop is at the starting
position for the next revolution. When the loop is in the first
half of its revolution, it will be evident that all projections of
the line OP are above the meiin horizontal axis of the diagram,
and the corresponding voltage values will be considered as
positive ( 4~ ); when the loop is in the second half of its stroke,
the projections are below the horizontal axis and the voltage
values are then negative (— )• Of course, the voltage passes
through the same variations in strength and direction during
the second and all succ:eeding revolutions.

4. The Sine Wave. For purposes of calculation, it is
desirable to reduce the relations shown in Fig. 18 to mathe-
matical form, and an understanding of tne trigonometrical
functions of right angle triangles p

will render this analysis easy. X. SIN O-gk

A right angle triangle, such as >^^V. COS 0=85

that shown in Fig. 19, is a *'V ^s^ 2p

triangle in which one of the "^^/i^ jjl]^ OA

angles is a right angle, i. e., one '^Oo\ 9 ^x.

of 90°; the other two angles are ^ ' * ' ^

known as acute angles, and are ^.^ ,9 Functions of the Right
each less than a right angle. Angle Triangle

The side OP, opposite the right

angle ei>d in Fig. 19, is known as the "hypotenuse," while the
other two sides PA and OA are the legs of the triangle. The
quotient obtained by dividing the length of the leg AP by
hypotenuse OP is known as the sine of angle G (Greek letter
"theta"). The quotient obtained by dividing leg OA by the
hsrpothenuse OP is known as the cosine of 6 . The quotient
obtained by dividing leg AP by leg OA is known as the ianfeni
of O. In right angle triangles, therefore, the fraction ob-
tained by dividing the side opposite a given angle by the
hypotenuse is the sine of that angle; the cosine of that angle
is the fraction obtained by dividing the leg adjacent to that
angle by the hypotenuse; and the tangent is obtained by
dividing the length of the leg opposite the angle by the length
of the leg adjacent to that angle. A litde study of Fig. 19

Sa ALTERNATING CURRENT SiCNALINC.

will make it plain that the sine of angle 6 is the cosine of
angle P, and that, vice versa, the sine of angle P is the cosine
of angle 6. The sine of angle d is generally abbreviated to
sin 0; the cosine of the same angle to cos 6; and the tangent
to tan 6. For an angle of given size, the above values are
always constant, regardless of the size of the triangle. Tables
of sines, cosines and tangents for various euigles will be found
in the latter part of this book. For example, the sine of a 30 **
angle is 0.500, and the cosine is 0.866, and the tangent 0.577;
for a 45 ° angle, the sine is 0.707, as is also the cosine, the tan-
gent being 1 .

With the above facts in mind, and referring again to Fig. 18,
it will be evident that, as line OP swings around from Pi to P2,
an angle, say G, is covered, and that the vertical projection
PjS of line OP2, representing the voltage generated at point

P2 is simply equal in length to the ratio y.-j x OP2, which is no

more or less than the sine of angle 9, through which the loop
has moved from its starting position, multiplied by the maxi-
mum voltage generated when the loop is horizontal as in Fig.
16. At any other point in the revolution, the voltage gener-*
a ted is equal to the sine of the corresponding angle through
which the loop has moved from the starting position multiplied
by the maximum voltage generated as before. Therefore:

e = E sin 9 (2)

where e is the voltage being generated at any instant, £ is the
maximum voltage and 0 is the angular position at the loop

|- at that instant.

With the generator shaft revolving at constant speed, there
is, of course, a fixed relation between time and angular posi-
tion of the loop, and, therefore, angle 9 is capable of further
analysis. The unit of length is the foot, and linear speed
is often given in feet per second, but, obviously, such a system
of measurement would not apply to angular sp>eed, and, con-
sequently, angular speed is always given in radians per second
in mechanics. Taking a circle of any diameter, an angle like
a piece of pie can be cut out so that the part of the circum-

^ ference of the circle which the angle cuts out is just equal in
length to the radius of the circle; that angle, called a radian, is
used as the unit of angular measurement, and is of constant
value for circles of all diameters, since the circumference

THEORY OF ALTERNATING CURRENTS. 39

varies directly with the diameter. As everyone knows, the
circumference of a circle is -3. 1416 times the diameter; the con-
stant 3.1416 is generally represented by the Greek letter tt
(pi). Since the diameter is twice the radius, a litde reflection
will show that there' are 2 ' radians in a circle of 360°; a

360
radian is consequently eqtial to ^ — ^ . .., . = 57.30®. If,

therefore, the shaft of the alternator shown in Fig. 1 5 is turn-
ing at a speed of n revolutions per second, its angular speed
is:

p = 2 77 n (3)

where p is the angular speed in radians per second. After i
seconds, reckoning time for position Pi, in Fig. 18, as the
starting point, the shaft will have turned through some angle,
say 0, of px t radians. Hence, at any time t in the revo-
lution the voltage generated will be

e = E sin e (4)

= E sin pt

5. Definitions. The following definitions are derived
from the above discussion:

An alternating current, or electromotive force, is one which
varies continuously with time from a constant maximum value
■in one direction to an equal maximum value in the opposite
direction, repeating the cycle of values over and over again in
equal intervals of time. Alternating currents are not neces-
sarily purely sinusoidal, as ^hown in Fig. 18, but most com-
mercial alternators produce waves which closely approximate
pure sine curves; for our purpose it will be satisfactory to base
our calculations on sine waves.

The period of an alternating current is the time taken for
the current to pass through one complete set of positive and
negative values, as shown in Fig. 1 8.

When an alternating current passes through a complete set
of positive and negative values, as shown in Fig. 18, it is said
to pass through a cycle.

The frequency, or number of cycles, per second, is the num-
ber of periods per second.

The number of alternations, generally given per minute, is
the number of times the current changes direction from posi-
tive to negative, and from negative to positive, per minute.
Obviously, in each cycle, there are two alternations. Frr

ALTERNATING CURRENT SIGNALING.

quency may, therefore, be given either in cycles per second or
alternations per minute. On this basis, a 60-cycle generator
gives 7200 alternations per minute.

6. Commercial Multipolar Alternators. The above
rules and definitions have been deduced from a consideration
Af the simple alternator shown in Figs. 13 and 16, but they
may be applied equcJly well to all alternators, no matter how
large or complicated. Of course, few commercial generators,
with the exception of alternators direct driven from high
speed turbines, are as simple as the on6 discussed. Where
heavy reciprocating engines are used to drive alternators, the
speed is, of necessity, comparatively low, and for commercial
frequencies and voltages a generator with a large number
of field poles, like that shown diagrammadcally in Fig, 20.
is used.

The alternator in Fig. 20 has eight field poles magnetized

by direct current fed from
a separate small D. C.
generator, known as an
exciter, which latter is
generally driven from the
same shaft as the arma-
ture of the alternator, as
at the left in Fig. 21,
which shows a large
multipolar alternator com-
plete with its slip rings
and exciter. It is to be
observed in Fig. 20 that
the voltages generated in
adjacent armature coils
are in opposite directions
at each instant, but by
reversing the connections
of alternate coils, as indi-
cated by the dotted lines,
these electromotive forces act in series and do not oppose each
i»ther. In multipolar alternators the frequency is:

Fig. 20. Armature Winding
8-Pole Alternator

* 2 ^60

(5)

THEORY OF ALTERNATING CURRENTS, 41

where P is the total number of field poles and n is the tpeed of
the atmature in rev. per min. If the alternator in Fig, 20 is
running at a speed af 375 r. p. m.. the frequency would be
t = ~X -Tn ~ " cycles per second
In such multipolar alteinators, the total voltage generated
acroB* the slip tings is

KP4,nZVolt« , .

100.000.000 ^'

where K is a factor depending on the ratio of breadth of pole
face to the sftacuig of the poles, as well n> on the diatribution
of the winding on the armature. P is the number of poles. 4 **
the magnetic flux per pole, n is the anDBture speed in revolu-
tions per minute, and Z is the total number of armature con-
ductors. This equation, it wiU be seen, is simply > devel^>-
ment of the equation given previously for the simple (Jter-

7. Turbo-Alter »tora. Steam turbines operate most
efBcienlly at high
•peeda and, in or-

date the alternators
to these conditions
with the commer-
cial frequencies of
25 and 60 cycles,
the number of field
poles roust be re-
mum. Many of
these turbo-alterna-
tors run at speeds
a« high as 3600 r. p.
m.. and have but
two field p<Je«. In
these cases, the field
magnet is the rotat-
ing element,
s easier to support

Fii.2l. AlUrni

and insulate the high voltage armature conductors c

(

42 ALTERNATING CURRENT SIGNALING.

outside stationary member; it is hardly necessary to
elaborate on the fact that it makes no difference which
element rotates, as only relative motion between field
and armature is necessary. On account of their high speed,
these machines generate a tremendous amount of power for
their size, as compared with reciprocating engine-driven al-
ternators.

8. Measurement of Alternating Currents and Volt-
ages. With currents and electromotive forces varsdng so
widely in magnitude from instant to instant as do alternating
currents, or e.m.f.*s of sinusoidal form, what is the meaning of
the terms ampere and itoft when used in connection with alter-
nating current circuits? The current at any instant i x^
known as the instantaneous current at that time, and is des-
ignated as /; the instantaneous e.m.f. is similarly denoted as
e. The maximum voltage, as before explained, is generated
when the number of flux lines being cut is the greatest, and is
designated as E, while the maximum current is denoted as I.
R^erring to Fig. 18, which for the present discussion, we shall
take to represent an alternating current of electricity, the
average value of that current is, of course, simply the average of
all the vertical ordinates, or heights, of the half wave extend-
ing along the horizontal axis between points 1 and 7; that is,
the horizontal half period axis 1 -7 would be divided into, say.
seven equal parts, as shown, and the average current would
be found by adding up the lengths of all seven vertical lines
drawn upward to the wave outline from points 1, 2, 3, 4, 5, 6
and 7, and then dividing the sum of these lengths by 7; the
average value of the voltage would be similarly found.

None of the above values are, however, convenient for
purposes of calculation. In direct current circuits, the rate
at which heat is generated by a steady current of I amperes
flowing through a resistance R ohms is equal to the square of
the current, multiplied by the resistance, or I R. Likewise, the
rate at which heat is generated by an alternating current of
instantaneous value /, through the same resistance, is i R; that
is, the average rate at which heat is generated in that circuit Is
R multiplied by the average value of ^. Now, a steady direct
current which would produce the same heating effect as the
fibpv^ alternating current would b^ pn^ whose square is equal

THEORY OF ALTERNATING CURRENTS. 43

■-- I -ir-r-r ■_!__ __M_ ■■ I

to the average value of i^ of the alternating current; the actual
value of the alternating current would, therefore, be equal to
the square root of its average i^. Thus, instead of taking the
average of a large number of ordinates, or heights, of the half
wave, as in the previous case, we must now take the square root
of the average of the squares of all these ordinates. This square
root of the average of the squares of the alternating current
over a complete period is called the roof mean square, or the
effectioe value of that alternating current. On this basis, one
ampere alternating current will produce the same heating effect
in a given resistance as will one ampere D. C. Similarly, the
square root of the average of the squares of an alternating
electromotive force over a complete half period is called the
effective value of that alternating e.m.f. v

In specifying the value of an alternating current as so many
amperes, or an alternating e.m.f. as so many volts, these
effective values are always meant, unless something is stated
to the contrary. The principal reason for selecting this par-
ticular function of the instantaneous values of an alternating
current or electromotive force as the practical measure of
current or voltage, is that the deflections or readings of all
ammeters or voltmeters used in alternating current measure-
ments are directly proportional to these effective values; fur-
thermore, it makes the direct current ampere and the alter-
nating current ampere equal, in that they will produce the
same heating and do the same work in passing through a
given resistance. All A. C. instruments indicate effective
values, which are obviously quite different from average
values.

PHASE RELATIONS— VECTOR DIAGRAMS.

9. Phase. When an alternating electromotive force ig
E E

Fig. 22. Current and Voltage in Phase

ALTERNATING CURRENT SIGNALING.

impressed across a dead resistance* the current varies instan-
taneously with the voltage; in other words, as the voltage rises
and falls, and changes direction, the current flowing through
the resistance rises and falls, and changes direction, at the
same time as the voltage. This condition is clearly shown in
Fig. 22, where current I and electromotive force £ are said to
be in phase^ because th^r maximum and zero values occur at
the same instant.

10. Lagging and Leading Currents. In many cases,
however, alternating e.m.f.'s are impressed across coils con-
sisting of mcuiy turns of wire Qf ten wound around iron cores,
and in these cases the current is choked back when It tends to
increase as the voltage rises, and persists when the voltage
falls, as will hereafter be explained. The coil of wire produces
an induciance etfect in the circuit, and causes the current to

Fig. 23. Current Lagging Behind Voltage

lag behind the electromotive force, as shown in Figi 23. The
basd line along which the curves are laid is divided off into
degrees — 360^ for each cycle to correspond to one complete
revolution of the loop ^hown in Fig. 1 5. The number of de-
grees by which the current lags behind the voltage is known
as the lag angle of the current with respect to the voltage, and
is designated as 8 in Fig. 23. Conversely, the electromotive
force leads the current, and in the same sense the angle 8 is
the lead angle of the voltage with respect to th^ current.
Again, the current and voltage are said to be out of phase by
an angle of 8 degrees.

11. Vector Diagrams. Alternating currents and Volt-
ages may be represented by the length, position and direction
of a line, called a Vector. Thus, two curreikts may be repre-

THEORY OF ALTERNATING CURRENTS. 45

^— M^— — I ■ ■ ■ ■■ ■ ■

seated (1 ) in magnitude :by two lines having lengths propor-
tional to the intensities of the currents; (2) in relative angular
position, or phase, by the angle at which the lines, extended if
necessary, intersect; and (3) in direction by arrow heads
placed upoxi the lines. Vectors may be combined or resolved
intojf components by the well known parallelogram of forces..

Vector diagrams of sinusoidal currents and voltages render
the 'study of phase relationsbips /quite simple. Simple dia-
grams of this character are show^ at the left of Figs. 22 and 23,
Vhere lines OE and OI revolve at a uniform rate of n revolu-
tions per second, equal to the frequency in cycles per second,
about point O in the direction of the arrow; since the lengths of
the vectors OE and OI are constant the paths of the end of these
lines will be circles, not necessarily of the same radius, as there
is no connection between the scales to which OE and OI are
drawn, one representing in length the maximum volts, and the
other, nuudmum amperes. The rotating lines OE and OI,
from whose^ vertical projections the current and volt^e waves
shown in Figs. 22 and 23 are constructed in the same manner
as the sine curve shown in Fig. 18, are said to "represent" the
sinusoidal current I. and the sinusoidal e.m.f. E, respectively.
In such diagrams, rotation is always assumed as taking place
in the counter-clockwise direction, as indicated by the arrow;
when two vectors are separated by a given phase angle, the
vector farthest around in the counter-clockwise direction is
said to be leading in phase, the other vector naturally lagging
by the same angle.

The proper representation of alternating electromotive
forces and currents by means of the vector diagram requires
that:

1. The given currents and voltages must be of the
same frequency, and, in addition, they must be of harmonic
character; that is, at any instant, the current or voltage
must be proportional to the length of the projection of th
line OP against the vertical, as shown in Fig. 18.

2. The direction of voltages and currents must be in-
dicated by arrow heads on the vectors.

3. The different vectors entering into the constructioi
of the diagrams must be constant in their angular relatione
to each other.

ALTERNATING CURRENT SIGNALING.

4. In addition to the above, it is desirable to scale the
lines of a vector diagram in terms of effective values,
rather than mcudmum values, because effective values are
alwayB giveii by measuring instruments and are used in
numerical calculations; of course, when laying out sine
waves, as in Fig. 22 cuid 23, it is more convenient to
use maximum values, as the corresponding instantaneous
values can be secured by simple projection.

For example, in Fig. 22 the current and e.m.f. are in phase,
and, consequently, their vectors shown at the left of the figure
are not separated by any phase angle; this relationship is
maintained throughout the revolution. On the other hand, in
Fig. 23, the vectors OI and 0£ are separated throughout their
revolution by phase cuigle 6 , by which the current lags be-
hind the e. m.f.

12. Vector Addition of E.M.F. 'S. Take, for example,
two alternators A and B (Fig. 24) connected in series, and as-
sume they are similar in all respects, being driven at the same

speed and possess-

I ing equal frequency.

/^^ If the three volt-

meters are con-
nected as shown,
voltmeters E^ and
Elg, will indicate, re-
spectively, the volts
due to alternators
A and B, whereas
E. will measure the
volts across the two
machines in series.
If the volts meas-
ured by E are equal to the arithmetical sum of E^ and
£2* the two alternators would, of course, be in phase, but as
a rule the reading of E will be smaller than the simple
sum obtained by adding Ei and E^. We will suppose these
three values, Ei, Eg cuid E, to be known. From the center O
of Fig. 24, describe a circle of radius OE, the length of which
represents voltage E. Now, draw OEi in any direction to rep-
presoit the volts E|. From Ei as a center, describe an arc

Fig. 24. Vectorial Addition of Voltages

THEORY OF ALTERNATING CURRENTS.

1 r'^^^ ►.A

Fig. 25. Determination of Resultant
Voltage

of radius EiE. the length of which is proportional to the volts
Eg; it will cut the arc already drawn at point E. Join OE and
complete the parallelogram OE^ EElo* The angle 9 between
the two component vectors OEj and OE12 is then the angle oi'
lag, and is, therefore* the phase difference between the two
voltages produced by alternators A and B.

The question of compounding two or more alternating forces
in an electric cir-*
cuit now becomes a ^

very simple matter.
Thus, in Fig. 24, had
we been given; the
two voltages Ej and
E^ and the phase
ditference 6 (instead
of the three volt-
ages), we could have
calculated the total
e.m.f. E and have
ascertained its phase
relation to its two
components by merely constructing the parallelogram of
forces OEi EE2 in the usual manner.

As an example, let us suppose that there are three distinct
alternating e.m.f.'s — ^A, B and C — of the following values, all
combining to produce one resultant e.m.f. in an electric
circuit:

A = 200 volts
B = 150 volts
C = 100 volts

We shall also assume that B lags behind A by exacdy 90'',
while C leads A by 35 **. Draw the three vectors OA, OB and
OC in Fig. 25 to a suitable scale, and in such directions that
the angles AOB and AOC are, respectively, 90** and 35°, bear-
ind in mind that OB must be drawn behind OA, while OC
must be drawn in advance, lead angles being laid off in a
counter-clockwise direction, as previously explained. First
construct the parallelogram of forces OBrA, giving Or as the
vector resultant of voltages OB and OA, then combine result*
ant Or with voltage OC by parallelogram OCRr, giving OR
as the final resultant of all three initial voltages. The length

46 ALTERNATING CURRENT SIGNAUNC

- - - I ■- rr ~ — \ '

of the line OR, measured by the same scale as the three
component vectors, gives us the value of the lesultant e.m.f.,
in this case 297 volts. If angle AOR is scaled it mil be
found that the resultant voltage OR lagiB behind component
OA by \%\

CIRCUITS CONTAINING
RESISTANCE, INDUCTANCE AND COMBINATIONS

THEREOF

13. Ohm's Law Applied to A. C. Circuits. In direct

current circuits Ohm's Law is expressed as:

E
I = ^ and the corollary E === IR (7)

Where I is the current in amperes caused to flow in a circuit

of R ohms by E volts. The same law holds also in alternating

current circuits, providing the proper interpretation is put on

the term R, for, due to certain inductance effects, presendy to

be described, the apparent resistance in alternating current

circuits is often many times the dead or ohmic resistance in

the circuit and Ohm's Law has to be amplified to:

E £

I = — and E = IZ and Z = y ' /g\

where Z is the impedance, representing the total apparent re-
sistance of the circuit in ohms.

14. Case I — Circuits Containing Resistance Only. In

the case of a circuit containing a dead resistance R only»

Z = R €Uid equation (8) becomes:

E E

I = ^ and E = IR and R = Y (9)

The current and voltage are in the phase. The vector dia-
grani and the corresponding current and voltage waves in
proper phase relationship are shown in Fig. 22.

' Example: An electromotive force of 220 volts, frequency
60 cycles, is impressed on a circuit of a total dead resistance
of 1 00 ohms. What is the current?

From equation (9) it will be evident that this current in the
above circuit will be the quotient obtained by dividing the
voltage 220 by the resistance 1 00 ohms, or 2.2 amp.

15. p Case II — Circuits Containing Inductive React-
nee Only. EUectric circuits possess inertia. In order to

THEORY OF ALTERMATUdG CURR£NT^ '49

form a mental picture of this property of an electric circuit.'
consider a flywheel rotating in a perfectly frictionless manner.
Such a flywheel once it has been put in motion will continue
to revolve for any length of time at undiminished speed,
vrithout requiring a further application of force. But a force
had to be applied to bring it up to speed, and exactly the same
amount of energy as was put in it is now available for
doing Work and will be given back by the time the flywheel
has been brought to rest.

The above is a fair physical analogy of what happens in ^the
case of an A. C. generator impressing an e.in.f. on a coil of
wire. It is assumed that the reader is aware of the fact that,
when a current flows in a wire, that wire' is surrounded cir-
cularly by a magnetic field of flux lines; when the current
starts to flow, the flux lines spring outward circularly with the
wire as a center, just like the ripples of water which are created
when a stone is thrown into a pond. The intensity of the
magnetic field about the wire at any point is dependent on
the strength of the current flowing in the wire, as well as the
distalice of the point from the wire. If the current alters its
value, the field is also altered, increasing with increase of cur-
rent and decreasing with decrease of current, finally collapsing
on the wire again when current ceases.

' It will be evident, therefore, that, when an increasing electro-
motive iottb is impressed across a coil of many turns of \^re,
cuid a current starts to flow, lines of magnetic flux spring out-
wardly in ebcpanding circles from each turn of the coil, and
cut the other turns, producing in them a secondary electro-
motive JForce, which will be found counter or in direct opposi-
tion to the impressed e.m.f. driving the current through the
coil; this action cuts the value of the current at cuiy instant
down below what it would otherwise have been, for part' of
th^ impressed voltage is taken to balance this counter electro-
motive force. On the other hand, when the impressed v6lt«
age falls* and the current tends to decrease in turn, the flux
linies start to collapse toward their respective turns, and in so
doing cut the other turns, generating in them a voltage in the
same direction as, and tending to assist, the falling impressed
voltage to maintain the current above what it otherwise
would be. ^

The magnetic field is a definite seat of energy and require

50 ALTERNATINC CURRENT SICNALING.

for its prcxiuction, therefore, a definite expenditure of energy,
determined in amount by the flux and the turns in the coil
with which the flux circles are linked. These linkages of flux
with turns constitute one of the most important factors in
alternating current circuits. The number of such linkages for
an dectric circuit carrying one ampere is known as the
coefficietd of sdf induction, or, briefly, the aelf-inJudance of
the circuit, being denoted by the symbol L. When the num-
ber of linkages of flux with turns due to one ampere flowing in
the circuit is 100,000,000, the circuit is said to have a self-
inductance of one henry. Stated in another way, a circuit has
an inductance of one henry when one volt, exclusive of the
e.m.f. required to overcome dead resistance, will cause the
current to change at the rate of one ampere per second. The
choking effect due to self-induction is the seat of an apparent
increase in the resistance of the circuit and in this, of course, the
frequency is an important factor. As a matter of fact a
mathematical analysis will show that in a circuit having a
self-inductance of L henrys the apparent increase in resistance
due to self -inductance is Lp ohms where p = 2itn, n being the
frequency as in equation (3).

So long as the current in the circuit remains constant in val*
ue, thereis no expenditure of energy in maintaining the field ; this,
of course, excludes the energy dissipated as heat in the electric
circuit itself. If, however, the field increases, a reaction will
be developed which must be overcome, requiring an expendi-
^re of energy in the circuit. If, on the other hand, the field
diminishes, there will be a reaction in the opposite direction
to that first considered, and, in virtue of this, energy will be
returned to the circuit. This reaction in each case takes the
form of an electromotive force, called the e.m.f. of self-induc-
tion, whose magnitude depends on the rate of change of link-
ages of flux and turns of wire. Every signalman has noticed
that, when the circuit of a pair of high resistance slot magnet
coils or relay coils carrying current is opened, there is a bright
spark and a "back kick" which is capable of giving a consid-
erable shock; this counter e.m.f., which is many times the
original impressed voltage, is simply due to the lines of mag-
netic flux collapsing on the coils, and thus generating a high
voltage when the current is suddenly interrupted. Similarly,
II an attempt were made to suddenly stop a heavy rotating

f THEORY OF ALTERNATING CURRENTS. 51

'^mwm^^a^-. iM—i.i iii _ i. i_ ■ -j u —m ■ ' " ■ ^i — ^ ~

flywheel by slipping a bar between the spokes and the engine
frame* disastrous results would follow* due to the quick dis-
sipation of the energy stored up in the rotating mass.

Obviously, therefore, in the case of a circuit conveying an
alternating current, there will be an alternate increase and
decrease in the energy of the magnetic field, and this will give
rise to inductance voltages. Considering a complete period
of the current, it will be. found that during one-half of this
period energy is supplied by the circuit to the fidd, and dur-
ing the other half of the period energy is returned by the field
to the circuit. When- the current is increasing in value, the
establishment of energy in the field sets up an opposing e.m.f .;
which does two things: first, it makes the current reach a given
value later than would be the case provided no such e.m.f.
existed; and, second, it diminishes the maximum value which
the current reaches in a complete period. When the current
is decreasing, the field contributes energy to the circuit; the
value of the current at any instant, however, is not as small
as it would be if no energy of the magnetic field were given
back to the circuit, and, for this reason, the current again
lags with respect to the value which it would have were no
such induced e.m.f. present. Again, the greatest negative
value which the current reaches is less than the value n^ch
it would attain provided no energy from the field were returned
to the circuit. In the flow of a sinusoidal current in a sdf*
inductive circuit, the value of the current will be less than if
the self-induction were not present and the current will lag by
a certain angle with respect to the impressed voltage. In this
sense, an alternating current circuit containing inductance
possesses inertia just as does the rotating flywheel above
mentioned.

As has previously been stated, the voltage generated in a
conductor is proportional to the rate at which the flux lines
cut that conductor. Now, when an alternating current is flow*
ing through a coil, the rate at which the flux lines spring
outward from their respective turns is greatest when the
current is just starting to rise from zero, whether in one di-
rection or the other ; then the current is increasing most rapidly*
ior there is an instant when the current increases from zero to
a definite quantity — ^from nothing to something, and then the
rate of increase of current, and consequent magnetic flux;

52 ALTERNATING CURRENT SIGNALING.

which varies simultaneously with the current, is the greatest.
' Conversely, when the current is at its maximum, it is steady
for an instant at the top of the wave, and there the rate of in-
crease in current cuid flux is zero. The electromotive force of
self-induction, resulting from the change in magnetic flux, is,
therefore, greatest when the current is zero. Now. if any
current is to flow through the coil, this counter e.m.f. of self-
induction must be balanced by an equal and opp>osite e.m.f.
from the generator.

This is illustrated in the wave diagram in Fig. 26, where I
represents the current wave and — ILp the e.m.f. of self-

'MLp^E

-nip

Fig. 26. Circuit Containing Inductanca Only

induction, which, it should be noted, is at its maximum when
the current is zero, and is zero when I is ihcodmum; also, since
— ILp is a counter e.zn«f., it is laid oS negatively, as it is op-
posing the change in current. The balancing component
wave + ILp must be laid off in opposition and equal to—'- ILp:
a voltage E equal to 4" ILp volts, must therefore be impressed
on the circuit in order that current I may flow.

The above conditionis are represented vectorially at the left
of Fig. 26, which diagram may easily be derived from the cur-
rent and voltage waves, or may be constructed independently,
as follows: first, lay oS the vector I horizontally to correspond
in scale to the given current. As before stated the equivalent
resistance of the inductance L is numerically equal to the
quantity Lp in ohms, where p = 2 rn, as shown in equation
(3), The term Lp is known as the inductive reactance of the
circuit, and is always expressed in ohms. The reactive volt-
age drop in Lp is equal to the inductive reactance Lp multi-
plied by the current I, that is ILp volts, just as the drop in a
-dead resistance R is IR volts. This reactive drop vector — IL|^

THEORY OF ALTERNATING CURRENTS. 53

lags 90° back of the current, as previously explained, the bal-
ancing impressed e.m.f. vector -{- ILp being exactly equal in
length and opposite in direction to — ILp. When the two
vectors arc separated by an angle of 90°, such as I and — ILp
or I and + ILp, they are said to be in quadrcdure. In such a
circuit, containing only pure inductive reactance, as just de-
scribed. Ohm's Law in equation (8) becomes:

E E

^ = L^ = X <«^> i

E = IX ^ (II)

E '>V>

where X denotes the reactance Lp.

X = -J- (12)

1 6. Case 1 1 1 — Circuit Containing Capacity Reactance
Only. We have now to consider briefly the case of a circuit
containing pure capacity readcmce, this latter effect accom-
panying the alternate charging and discharging of a condenser
whose two terminals are connected to an alternator. The ca-
pacity^ inight consist of a condenser, fprmed by a long dead
ended cable containing two conductors carefully insulated
from each other, or the condenser might be composed of a
number of sheets of tinfoil piled up with sheets (^ glass or
paper between them, alternate layers of tinfoil being connect-
ed together to give the effect of two large metal sheets close
to, but thoroughly insulated from each other just as in the
case of the cable; in either case as long as the alternating cur-
rent is flowing in a positive direction, Current flows into the
condenser, which, therefore, becomes charged, but, as soon as
the curreiCit reverses, the condenser begins to discharge. The
maximum charge of the condenser, and, consequently, its
maximum back pressure or counter e.m.f., occurs just at the
mooient when the current is about to reverse, and this^ back
pressure or counter e.m.f., therefore, tends to help the current
reverse, the latter growing to a negative value much quicker
than it otherwise would do; this is just the opposite of what
occurs in a circuit containing inductive reactance, and, as a
consequence, in a circuit containing pure capacity reactance,
the current leads the impressed voltage E by a quarter of a
or 90^, whereas, as previously explained, the current

ALTERNATING CURRENT SIGNALING.

lags 90^ behind the impressed voltage E in a purely inductive
circuit.

Capacity effects are so minute in signal work as to be negli^
gible. with the single possible exception of transmission sys-
tems, and then only in the case they are very long; if, however,
by any chance it becomes necessary to run the transmission
underground in a cable, the capacity effect will be more no-
ticeable, and had best be investigated. The cable manufac-
turers will furnish data covering the capacity reactance of
their product, and from this the capacity reactance drop may
be calculated, this latter, of course, helping to neutralize the
inductive reactance voltage, with the result that a less volt-
age will have to be impressed on the transmission to force the
required current through it than would be the case if capacity
were not present.

17. Case IV — Circuits Containing Resistance and In-
ductance. In Case I above, we considered a circuit contain-
ing resistance only, and later, in Case 1 1 , one containing pure
inductance only; the latter case is purely theoretical, as all
circuits contain some resistance, however small, and, converse-
ly, all circuits, particularly A. C. signal circuits, contain in-
ductance. The general case, therefore, is one in which the
circuit contains resistance and inductance.

t*G*l

ILp E...

:iR

N^V^

-ILp

Il>

Fig. 27. Circuit Containing Resistance and Inductance

Fig. 27 illustrates this general case, I being the current wave.
— ILp the wave of the counter e.m.f. of self-induction, ILp
the balancing wave for the latter, and IR, naturally in phase
with the current, the wave corresponding to the drop in the
given resistance R. In order that current I may flow through
this circuit, the alternator must not only supply enough volt-
age to compensate for the resistance drop IR, but, in addition.
It must supply the component wave ILp to balance the in-

THEORY OF ALTERNATING CURRENTS. 55

ductive drop; the total impressed voltage E must, therefore,
be equaL to IR-{-ILp> the wave E, therefore* being plotted by
adding, algebraically, the verticals of waves IR and ILp at
each instant along the horizontal time axis, due attention
being paid to the fact that IR cuid ILp are sometimes in oppo-
sition.

The corresponding vector diagram is shown at the left of
Fig. 27, which diagram may be derived direcdy from the cur-
rent and voltage waves, or may be constructed independendy,
as follows: first, lay oS the current vector I horizontally, and
superimpose on it the voltage drop IR, obtained by multiply-
ing the current I amperes by R ohms, I and IR. of course,
being direcdy in phase. The impressed voltage for balancing
the inductive reactance voltage is ILp volts in quadrature with
and leading the current. The total impressed voltage E is the
vectorial sum of IR and -f IL<p, and is simply the diagonal of
the parallelogram of which IR and ILp are two right angle
components. This resultant E is the hypotenuse of a right
angle triangle, and is equal, in volts, to the square root of the
sum of the squares of IR and ILp, since thehypothenuse of a
right angle triangle is equal to the square root of the sum
of the squares of the two legs.

Therefore,

E =

V (IR)2

+ (ILp)»

(13)

and by Ohm's

Law,
I =

equatiMi
E

(8)

(14)

V (IR)«

+ (ILp)»

and

Z =

(15)

V (IR)'

' + (ILp)»
I

(16)

V(R)«

+ (Lp)«

(17)

Z =

VR* +X»

(18)

finally.

X = •Z^ — R^ (19)

where Z !• the total apparent resistance, called the imptianct

56 . ALTERNATING CURRENT SIGNALING.

of the circuit. and the quantity X is the abbreviation for the
term Lp, the inductive reactance. ,

From the explanation of trigonometrical functions given in
the first part of this chapter, it will be evident, from Fig. 27
that the lag angle G of the current 1, with respect to the imp-
pressed total e.m.f., can be easily calcu&ted in advance for:

IR IR

CosO =

VP (R2 +X2)
R

^ V(IR)2+(ILp)» i

IR I

VR* +X2 (20)

and on looking up the number representing this ratio in the
table of cosines in the back of the book,, the corresponding
angle in degrees \yill be found.

18. Amplitude Factor. It is to be noted that equations
(10) to (20). inclusive, are based on effective values, whereas
the vector diagrams in Figs. 26 and 27 are laid out with vec-
tors representing ^'^maximum values, in order to ehow their
direct connection with the development of the current and |
voltage waves. Of course, effective values are less than the
corresponding maximum values, but there is a definite rela-
tion between the two values. The ratio of the maximum
value to the effective value is known as the amplitude factor,
which, for sine waves, is equal to 1.414. Therefore, in the
above case the maximum values shown in the diagram? in
Figs. 26 and 27 may be arrived at by multiplying the values

in equations (10) to (20) by 1.414.

19. Practical Measurement of Impedance and Re-
actance. In actual practice, the numerical value of X can
be determined as follows: The dead resistance of the wire in
the coil or instrument in question can be calculated when the
length of wire and its resistance per foot is known, or the same >
result can be arrived at by passing a direct current of I am- |
peres through the wire; by Ohm*s Law, equation (7) R, the
resistance of the coil in ohms, is equal to the voltage E, neces-
sary to force the current through the coil, divided by the pur-
rent I in ampeies. When an alternating e.m.f. E vol|9 of a
riven frequency is impressed across the same coil or, instru*

THEORY OF ALTERNATING CURRENTS. 57

ment, a certain current of I amperes will flow, which may be

measured by an ammeter, so that, by equation (8), Z =

^ ohm^; then, since R is already known, the inductive react-

ance X in ohms is X = V Z'* — R from equation (19)
With a higher frequency, X would be greater, since X = Lp
and p = 2'n, where n is the frequency in cycles i>er second,
as per equation (3). With a lower frequency, the term X
would be smaller, since n is smaller. In fact, if n were zero,
as would be the case with a direct current, then the term X,
t!ie inductive reactance, would disapi>ear entirely, and then
the flow of current would be limited by dead resistance only.
So, with a given voltage, the current flowing through a coil of
wire Mrill increase in volume with decrease in frequency, and
will fall oS as the frequency increases.

20. Calculation of the Inductance of a Coil of Wire.

The inductance of a coil wound on a given spool is propor-
tional to the square of the number of turns N of wire. For
example, a given spool, wound with No.i 16 has 500 turns and
an inductance, say, of 0.0025 henry: the same spool wound
•with No. 26 wire would have about «ight times as many turns,
and its inductance would then be about 64 times as great as
before, or 0. 16 henry. The inductance of a coil of given form
is also proportional to its linear dimensions, the number of
turns remaining constant. For example*^ say a given coil has
an inductance of 0.022 henry, a coil three times as lars;e in
diameter, length, etc., but having the same number of turns
of wire, has an inductance of 3 x 0.022, or 0.066 henry.

Tlie inductance in henrys of a coil of wire wound in a thin
layer on a long wooden core of a length of / centimeters and a
radius of r centimeters, is ,

_ 47r2r^N^

/x 1,000,000.000 ^ ^

in which N is the total number of turns of wire in the coil. The
equation is strictly true for very long coils wound in a thin
layer; but the same equation is also useful in calculating ap-
proxi][nately the inductance of sho; t thick coils. Thus, a coil
of 50 centimeters long, conta<nmg'100' ttiriis of wire wounf'

5* ALTERNATING CURRENT ^IGNALINC.

» I ■ I I I II ..1 ■ ■■— ■ ■ ■ -■ mtm* ^ ■— ■■ ■■■■ .^^ ■ I ■■! ■■■■■■■ ■ ^ ■,,■■■■ ■ ■— ^— ^■^■■^,■ ■ ■ , , ■ ■ ,„■ i ^ ^^

around an average radius of 4 cendmetefs, has an inductance
closely equal to:

4 X (3.1416)' X (4)* X (100)^ nnnni^k nj-,

^ 50x1.000.000.000 ^•<^' ' ^*^ <22)

Of course, if the wire in the above coil were wound around
an iron core instead of one of wood, the inductive action would
be enormously increased in proportion to the permeability of
the iron core.

POWER IN ALTERNATING CURRENT CIRCUITS.

21. Apparent Power or Volt-Amperes. In direct cur-
rent circuits, the power W in watts is:

W = EI (23)

Where E is the electromotive force necessary to force a cur-
rent of I amperes through the circuit. In alternating current
circuits, the same equation holds, provided the current and
voltage are in phase, which, however, is rarely the case. Of
course, the instantaneous power is:

w = ei (24)

where e and i are the instantaneous volts and amperes re-
spectively, but sometimes the generator is suppljring power to
the circuit, and at other times the circuit is returning power
to the generator, as has previously been explained. What we
are interested in is the average power supplied to the circuit.
In an alternating current circuit, the apparent power is
given in ooUamperes, this term covering the simple product of
the volts E necessary for forcing a current of I amperes
through the circuit, the voltage and current values being ef-
fective values, as indicated by the ordinary meters.

Voltamperes = IE (25)

Tlie apparent ix>wer in voltamperes is greater than the true
or average power, because part of the apparent power, is re-
turned to the generator.

22. True Power or Watts. It will be shown below
that the true taatts or aoerage power delivered to the circuit is:

W = IE cos e (26)

Where I and E are the effective current and impressed voltage,
respectively, and 0 is the phase angle between the current I
AQd the voltage E.

'*3* Power Factor. The quantity cos 8 is known as the

THEORY OP ALT£RNATiNC euftft£h4TS. ^4

*■

power Jatiar, and is the ratio of the true power or watts to
the apparent power in voltamperes.

Power Factor = cos 9 = 7^ ^*i

Of course, the power factor cos 0 can never be more than
unity, since the watts cannot be greater than the voltamperes.

24. Case I — Power in an A. C. Circuit Containing Re-
sistance Only. In this case, the current and impressed e.m.f.
are in phase, as has been pointed' out. In the general equation
(26) for power in an alternating current circuit. W = EI cos 0
but when the current and e.m.f . are in phase, the lag angle 0
is zero, and its cosine is unity. Therefore, the power equation
becomes, simjJy:

W = EI (28)

The above equations are illustrated graphically in Fig. 28
where the watt curve is obtained by multiplsdng the instan-
taneous volts and amperes at the various points in the period.

WATTS ^ WATTS

Fig. 28. Power in a Circuit Containing Resistance Only

It is to be noted that the power curve is a wave of double fre-
quency, as compared with the curves of e.m.f. and current.
The axis of symmetry of this power curve is distance W, cor-
res[>onding to the average watts above the axis of the e.m.f.
and current waves. Of course, the product it is cJways posi-
tive, even in the second or lower half of the period, because the
product of two negative numbers ( — e) x ( — i) is always posi-
tive in value; looking at the matter from what physiccJly takes
place, the circuit is cJways receiving power positively, and is
never delivering power back to the generator. The appareo*'

60 ALTERNATING CURRENT SIGNALING.

power in voitamperes is equal to the watts, and, consequently.

EI
^ Power Factor = pj- = 1 (29)

25. Case II — Power in a Circuit Containing Indue- >
tive Reactance Only. Of course, it would be impossible
practically to create a circuit containing inductive reactance
only, due to the fact^that all circuits must have some resist-
ance, no matter how smcdl; at the same time, the study of what
takes place in such a circuit is instructive, for here the current
lags 90° behind the impressed e.m.f., and the two are there-
fore, in quadrature.

|WATTS

Fig. 29. Power in a Circuit Containing Inductance Only

This condition is illustrated in Fig. 29, where the sine curve
W, obtained by multiplying the instantaneous volts and am-
peres, with due regard to positive and negative vsJues (a posi-
tive (+0 multiplied by a negative (-e), and vice versa, gives
a negative (-w), is a sine curve of double frequency, and its
axis of symmetry coincides with the axis of e.m.f. and current.

Here the power:

W = El cos 0

= EIxO (30)

= O

because the cosine of the lag angle 90° is zero. An examina-
tion of the watt or power curve in Fig. 29 will show that the
average power is zero, because, during the complete period,
iust as much power is returned to the generator as it delivers
the circuit: the negative and positive portions of the power
ve are equal, and their sum is therefore zero.

THEORY OF ALTERNATING CURRENTS.

The power factor (abbreviated P. F.)

PF =

EI COB Q Watts

_ O
~ EI
= O

EI Voltamperes

(31)

26. Case III— Power in a Circuit Containing Resist-
ance and Inductive Reactance. This is the general case,
met with in alternating current circuits. The resisteoice R
and inductive reactance X are such as to cause the current to
lag e ** behind the impressed e.m.f., as shown in Fig. 30, where
6 is an angle such that

cos 9 =

VR2+X2

as per equation (20).

Fig. 30. Power in a Circuit Containing Resistance and Inductance

This condition is shown graphically in Fig 30, plotted in
the manner previously described, where it will be seen that the
power curve is again a curve of double frequency with its axis
at a distance W above the axis of the e.m.f. and current waves.
At certain instants, the power is negative, at certain other
times positive, and the average power is the difference be-
tween the two. This is shown on the diagram by the loops
in the power curve coming part below and part above the axis
of the e. m. f . and current curves. The average power is f oimd
by subtracting the total area below from the total area above
the axis of the e.m.f. and current waves. It is important to
note/ therefore, that in the ordinary alternating current dt"

ii ALTERNATING CURRENT SIGNALING,

cuit the power is fluctuating. Part of the time the generator
delivers power to the circuit, and the rest of the time the cir-
cuit is returning power to the generator to run it as a motor.
This, then, is the general case, where:

W = EI cos 0 (32)

and the value of cos 6 is somewhere between zero and unity.
In the preparation of this chapter an att«»Jpt has been made
to explain the more important fundamentals of alternating
current theory. Those who are interested in the subject and
desire to learn more about it are advised to consult the stand-
ard text books, among which the following are easily available,
either at the public libraries or through loccJ book sellers.

1 . Estey — ^Alternating Current Machinery.

American School of Correspondence, Chicago, 111.

2. D. C. and J. P. Jackson — ^Alternating Currents and Al-

ternating Current Machinery.

The MacMillan Co., New York.

3. Pender — EJectrical Elngineering.

McGraw-Hill Book Co., New York.

4. Hay — ^Alternating Currents.

D. Van Nostrand Co.

5. Steinmetz — ^Alternating Current Phenomena.

McGraw-Hill Book Co., New York.

6. Steinmetz — ^Theoretical Elements of EJectrical Engi-

neering.

McGraw-Hill Book Co.. New York.

} 2 Vol.

7. Karapetoff — ^The Electric Circuit

The Magnetic Circuit
McGraw-Hill Book Co., New York.

Of all the books on alternating currents the most complete
are perhaps those by E. Arnold of Karlsruhe, published by
Julius Springer of Berlin under the general title of Die
Wechselstromtechnik,. They have been written with pains-
taking thoroughness and cover both from the theoretical and
practical standpoints, almost every phase of alternating
current working. At the present time they are available in
German only. -

0-'

CHAPTER III.

ELEMENTS OF THE
ALTERNATING CURRENT TRACK CIRCUIT

CHAPTER III

ELEMENTS OF THE
ALTERNATING CURRENT TRACK CIRCUIT.

1. Elements of an A. C. Signal System. In general, a
comi^ete A. C. signal system consists of the following:

(A) The track circuit control system, made up of

(a) Track relays, over whose points the signals are
controlled, sometimes jointly with line rela3^, depending
on the type of automatic block circuits used.

(b) The transformers for feeding the track circuits and
signals.

(c) The limiting resistance or impedance used between
the transformer and the track to prevent an injurious short
circuit current flowing through the track transformer with a
train in the block. ^

(B) The signals, which may be either of the semaphore
or light type.

(C) The transmission system paralleling the right-of-
way and supplying power to the transformers at the various
locations.

(D) The power generating system in the power house
supplying power to the transmission.

It is the purpose of this chapter to discuss the elements of
the track circuit, the other elements of the complete signal
system being covered in later chapters.

STEAM ROAD TRACK CIRCUITS.
End Fed and Center Fed Track Circuits.

2. End Fed Track Circuits. Practically all A. C. steam
road track circuits are end fed, that is, the track transformer
is located at the leaving end of the track circuit and the relay
which it feeds at the entering end; this arrangement is, there-
fore, exacdy similar to the general practice in D. C. track
circuit work, where a battery takes the place of the track trans-
former. ^ Fig. 31 illustrates the A. C. end fed track circuit

<6 ALTERNATING CURRENT SIGNALING.

with its dements a> used on ateam road*. The atandord aym-
bo) for an alternating current relay is that of the direct current
relay marked with an X across tiie ctuls as akowD.

Fig. 31— ElcmsDl o! Ili> End Fed Track Circuit

3. Center Fed Track Circuits. There is no Umit to the
passible length of an end fed track circuit, except the amount
of power rquired for its operation. While the amount of
power required at the track relay lerminala is. of course, con-
stant, regardless of the length of the track circuit, it must he
remembered that a large proportion of the current fed into the
track by the transformer is lost through leakage across the
track from rail to rail over the ballast and ties, just as is the
case in D. C. track circuits; in track circuits much over a mile
in length, this leakage factor increases rapidly as the track
circuit is extended, especially in the case of poorly drain-
ed cinder ballast and old water or brine aoaked ties. The cur-
rent lost in ballast leakage naturally causes a corresponding IZ
drop in the rails, which piles up in almost geometrical ratio
as the track circuit is made longer, so that, in the case of very
long track circuits, the transformer must supply a compara-
tively high voltage to the track before the relay will pick up;
at that point in the track where the transformer is connected
the voltage across the rails is obviously the highest, and here,
conaequendy, the current lost in ballast leakage ia the greatest,
the leakage current falling over gradually with the decrease

in volta^ acro»a the nuls as we proceed down the track to-

ELEMENTS OF THE A. C. TRACK CIRCUIT. 67

ward tite relay. It is desirable, therefoie. from the standpoint
of power economy, to keep the voltage at the tails opposite the
transformer as low as possible.

at the Cenb

Fed Track Circuit

So, if, for example, it is desired to operate a 15.000-foot
track circuit with a given type of relay, and the calculations
show thai an unreasonable amount of power would be required
(or an end M track circuit, then a center fed track circuit,
shown in Fig. 32. may be resorted to. In this arrangement the
track transformer is located at the middle of the track circuit,
feeding in either direction a relay at the end of the section;
thus, the voltage at the track opposite the transformer is much
less than would be thecase with anend fed track circuit of equal
length, and, due to this lower voltage, the leakage current
across the ballast near the transformer is cut down, the saving,
of course, falling olf as we proceed in either direction from the
transformer toward the relays. For purpioses of calculation,
a center fed track circuit may be considered as two end fed
track circuits joined together and fed jointly at their meeting
point. With the center fed track circuit, the voltage at the
track opposite the transformer will be the same as that re-
quired for one of the component end fed circuits, but the cur-
rent fed in the track from the transformer must evidently be
twice as great.

Where center fed track circuits are used, the signal oper-
ating circuit must be broken through points on both track
relays, for there is a time when the train is on the leaving end
of the track section, that relay A (Fig. 32) may pickup, due
to the fact that, as the train proceeds out of the leaving end of _

68 ALTERNATING CURRENT SIGNALING.

.1 '^l ,F ...

the bIock» its shunting action on the track transformer de-
creases and the voltage on the relay at the entering end of the
block rises. At that time, though, relay B at the leaving end
is shunted dead as the train is practically across it, so that, if
the signal control circuit is passed through the points of both
relays in series as shown, at least one relay is bound to be open
whenever there is a train en the track section, no matter at
what point.

Single and Double Eleznent Relays.

4. Single Element Relays. All direct current track re-
lays receive their power over the track; that is, the battery
connected to t!ie rails at one end of the track circuit supplies all
the power for the operation of the relay. The same may also
be said of the alternating current track relays shown in Fig.
5j and 32, where the transformer takes the place of the before
mentioned batteries; there are, of course, two track relays per
track circuit in Fig. 32, but both of them receive all of their
power over the rails. Such relays are called single element re-
lays; they have but one winding, although they may have two
or more coils interconnected in series or multiple, just as in
the case of the two coils on a direct current track relay.

I 5. Double Eleinent Relays. Long track circuits oper-
' ating with single element A. C. track relays are seldom used
I nowadays, because such track circuits are extravagant in the
way of power. A track circuit is nothing more nor less than
a smcJl power transmission system, and a mighty inefficient
one at that. The usual high voltage power transmission con-
sists of a generator located at one end of the system, feeding
current at a high voltage over carefully insulated wires to a
motor or other receiving device at the far end of the system;
the leakage between the carefully insulated transmission wires
is comparatively insignificant. In the case of a track circuit,
the track transformer takes the place of the generator in the
high voltage transmission system above mentioned, the rails
take the place of the transmission wires, and the track relay
takes the place of the load at the end of the system. But
the rails are not carefully insulated from each other, as are the
transmission wires in the first case; the rails are spiked down
• the ties, which may be water or brine soaked, and the bal-

CLEMENTS OF THE A. C, TRAGIC CIRCUIT. 69

last across the rails may be cinder, or some other more or less
c^dactive material. In any event, the ties and ballast con-
stitute a leak across the rails, and the track circuit transmis-
sion is, therefore, bound to be inherently inefficient. A track
circuit is a poor line over which to transmit power. The less
power transmitted over it, the better.

It wa6 with the above facts in mind that the so-called two-
element relay was invented. This type of relay is provided
with two separate and distinct elements on windings, one of
whiqh. called the trac/j element or winding, is connected to and
rieceives power over the raiFs as usucJ from the track trans-
former, while the other, called the local element or winding, re-
^6ive9 power directly from a transformer.

The turning effort exerted on the moving member of the
relay to close the contacts, is proportional to the product of
the current flowing in the track and local elements, with
c^ regard to phase relations, as will be explained in Chapter
rV. A given turning eti'ort can be produced on the contact
operating member by the interaction of two currents of me-
dium value in the two elements, or by a very small current in
one element and a very large one in the other element.

Only a very small amount of power, therefore, is used in the
track element of two-element relays, and so comparatively
Ijittle power is lost in the track circuit transmission, as only a
Iji^ttle has to be transmitted; only a small voltage is required
at the track traixsformer end of the track circuit On the
other hand, a comparatively large amount of power is delivered
to the local element of the relay from its local transformer: of
course, there is practically no loss of power between this trans-
former and the local coil of the relay which it feeds, because
the feeding wires are always well insulated, and they are also
generally very short.

Such two-element relays work on the motor principle; that
ifif both track and local elements must be simultaneouely
energized before any turning movement is produced in the
moving member of the relay to close the contacts. The local
eleinent is permanently connected to its transformer, and is
conse<|uently cJways energized, regardless of whether there is
a train on the track circuit or not. The track element is. of
course^, energized only when the track circuit is unoccupied,
for, when a train is on the track circuit, all the current is

ALTERNATING CURRENT SIGNALING.

shunted out of the track element of the relay. Some of th<
two-element relays operate on exactly the same principle as
does the ordinary direct current signal motor. In this anal-
ogy, the field coils and armature of the signal motor would
represent, respectively, the local and track elements of the re-
lay. It will be realized that, as long as current flows through
both field coils and armature, the motor'will continue to ro-
tate; but, if for example, the armature were short-circuited,
the motion would then cease, even though current were still
flowing through the field coils. The contacts of a two-element
track relay are never closed, except when current is flowing
through its track element, as well as its local element.

Two and Three-Position Relays.

6. Two-position Relays. Single element A. C. relays
are necessarily two-position relays; there is no element of per-
manent character to respond to changes in the polarity of the
single energized element, and, consequently, these relays are
exacdy comparable to the usual neutral direct current track
relays met with in steam road services. Single element relays
have but two positions; their front contacts are closed when
no train is on the track circuit, and these front contacts open
and the back contacts make, as shown in Fig. 3 1 , when a train
enters on the track circuit.

LIN£
TRANSFORMER

^ TRACK
ITRANSFORMER

O-^TRACK ELEMENT
^ LOCAL ELEMENT

Fig. 33~Two-eIeinent, Two-position Relays on an End Fed Track Circuit

7. Three-position Relays. Two element relays, on the
contrary, may work in either two or three positions. Fig. 33
represents the two-element relay working in two positi<nis

ELEMENTS OF THE A. C. TRACK CIRCUIT.

only on an end fed track circuit, although it would work
equally well on a center fed track circuit.

Due to the motor action previously described, the moving
member of two-element relays may be caused to rotate in one
direction or the other, depending on the relative direction of
the magnetic flux produced in the track and local coils by their
respective currents. As previously stated, the local element
is permanently connected to its feeding transformer, but by
means of a pole changer, as shown in Fig. 34, the polarity of
the track element, with respect to the local element, may be
controlled. In such a relay, the moving member is counter-
weighted to return to a central or neutral position, with all
contacts open, as shown at A, in Fig. 34, when a train is in the
block, and the track element of the relay is short-circuited.
When the track element is energized in one direction, as shown
at B, one set of contacts is closed, while, when the pole changer
between the track transformer and the track is swung over,
the direction of the moving element of the track relay is re^
versed, so that another set of contacts are closed, as at C, in
Fig. 34. In fact. Fig. 34 represents a polarized wireless sys-
tem of signaling, with alternating current track circuits,
where the usual polarized track relay used on D. C. track
circuits is replaced by the three-position A. C. track relay.
The two relays fulfill the same function, and, of course, may
be used for controlling signal indications in either three-posi-
tion or home and distant signaling.

Fig. 34— Polarized Wireless Track Circuit with Three-position Relays

8. Protection Against Broken Down Insulation Joints
with Two-element Relays. It is to be noted that, on ac-

72 ALTERNATING CURRENT SIGNALING.

<x>unt of the possibility of reversing the direction of movemelit
of the rotating element which actuates the contacts, perfect
broken down insulation joint protection can be secured with
two-element two-position relays by staggering or reversing
the polarities of adjacent track circuits. For example, in Fig.
33, the polarities of track circuits M and N are opposite at any
given instant, and, if insulation joints X and Y were to bre^k
down, relay B would be forced on its back contacts to open the
signal circuit. On the other hand, under similar circum-
stances, a single element relay might pick up with a short
. train at the far end of a long track circuit, because, if the in-
sulation in joints X and Y were in very bad shape, the ad-
jaceht transformer would be practically across track relay B.
A moment's reflection will make it evident that equal proteC'
tion Cannot be seciiz«d ^nM^^^flhtofte^position relays, although
certain schemes^ «»^ ^within the scope o( this book, have been
suggested However, even with three-position relays, it is
customary and advisable to stagger polarities on adjacent
abutting track circuits, so that, if both insulat^ joints break
downy a caution, and not a clear, indication will result. ^This
is illustrated in Fig. 34 where, with the track circuits unoccu-
pied, their polarities are staggered ;. th^ local windings of alter-
nate relays, such as B, are reversed so that the same contacts
may always be used for the caution and clear indications re-
spectively.

Statements have, been made above that "the polarity cf
the track element, with respect to the local element, can be
reversed.*' and that "the polarities of adjacent track circuits
can be reversed." Of course, the alternating currents are peri-
odically changing in direction, and the abov^ statements sim*
ply mean that at any given instant the polaritites are opposite.
During other portions of the cycle, positive polarities will
change to negative polarities, and vice versa, but op[>osite re-
lationship will always be maintained.

Transformers.

9. Track Transformers. This transformer, as its name
indicates, is used to supply current to the track. It may re-
ceive power directly from the high voltage transmission line,
as is the case in Fig. 32, or from the secondary coil of the main
line transformer shown in Fig. 33; track transformers are al-

ELEMENTS OF THE A. C. TRACK CIRCUIT.

ways provided with a number of taps on the track, or second-
ary. 6ide, so that, depending on the length of the track circuit
and its ballast leakage factor, the necessary voltage may be
impressed on the track to insure proper working of the relay.
Track transformers which receive power directly from the
transmission, as shown in Fig. 32, are generally housed in an
oil filled cast iron case, hung on a cross arm carried by the
pole on which the transmission is strung; track transformers
which receive power from the secondary of the line transformer
as shown in Fig. 33, are generally built up on a wooden base,
and are housed in the relay box at the signal location.

LuuuuuJi
pnrj pTTj'

UuuuuuJ

pnnnr

^T T

c*M k

la.

*-!-*

^ [

i I f

f-f

Fig. 35 — Multiple Feeding of Parallel Track Circuits

In double or multiple track work, it is the custom to feed
the two or more parallel track circuits from one transformer,
but in this case the track transformer should be provided with
a separate and independent secondary for each track circuit.
This practice is advisable since the rails of a track circuit are
' .4ncre or less grounded, depending on the nature and condition
of the ballast. Hence, relay C, Fig. 35, might remain picked
up with a broken rail at D, since current could flow from the
positive «ide of transformer A to the upper rail of the lower
track circuit, from M to N over the ground and direct to relay
C, the other side of which is connected to the negative side of
the transformer over the upper rail of the track circuit in
which the break D is located; furthermore, there is a bare pos-
sibility in the case of exceedingly poor wet ballast, of the relay
adjacent to transformer A being picked up with a train at the
extreme end of its track circuit (near E) if one of the insulated
joints between A and the relay broke down.

This etfect is naturally entirely dependent on the extent to

74 . ALTERNATING CURRENT SIGNALING.

which the rails are grounded and also on the ballcMt conduct-
ance. To guard against it, each track circuit had best be fed
from a separate secondary as at E, Fig. 35» the transformer
being provided with two secox^daries for this purpose. In the
<:ase of detector circuits, as used in interlockings, each track
circuit should likewise be separately fed, transformers with
four secondaries being of a convenient size.

10. Line Transformers. Any transformer connected
directly to the transmission line might, with perfect accuracy,
be called a line transformer, but in actual signal practice the
term has become restricted to a transformer with a primary
connected to the transmission, and one secondary of 55, 1 10
or 220 volts, this secondary being jointly used for supplying
power to the signal motors, slots and relay locals, and also in
the majority of cases to the separate track transformer shown
in Fig. 33 ; the signal lights may also be fed from the secondary
of the line transformer, but in most cases the primary of the
separate track transformer is provided with a 1 0-volt tap to
handle the lights. Such line transformers are commercial
articles, made in quantity and kept in stock by the manufac'
turers at all times, and are, consequently, quickly replaced;
in case of burnouts; furthermore, through their use, the sepa-
rate track transformer shown in Fig. 33 becomes relatively in-
expensive, as it need not be elaborately insulated for connec-
tion to the transmission line, since it is fed from the low ten-
sion, or secondary, side of the line transformer, and may be
housed in the relay box, without the oil filled case which would
otherwise be required.

11 • Combined Line and Track Transformers. In some
cases, a combined line and track transformer is used; its pri-
mary is connected to the transmission, and it is provided with
two secondaries, one being wound for 55, 110 or 220 volts, for
feeding motors, slots, and the local coils of the track relays, the
other being a low voltage secondary for feeding the track.
Such a transformer, shown in Fig. 34, generally costs more
than would be the case if a commercial line and a separate
track transformer were used, due to the fact that the combined
line and track transformer has generally to be specially made
up by the signal manufacturer to suit the conditions.

ELEMENTS OF THE A. C. TRACK CIRCUIT. 75

'-' • ... I I I ■■ .11. I > I ■ .1 ., I ■ ,

Track Resistances and Impedances.

12. Function. The gravity batteries used with the di-
rect current track circuit have an internal resistance varying
from one to four ohms per cell, depending on their physical
condition* and this inherent internal resistance prevents a
wasteful, and possibly injurious, short circuit curr^it from
flowing from the cells when a train is on the track circuit. In
the case of lead storage batteries, and some primary batteries
of the caustic soda type, the internal resistance per cell is only
a very small fraction of an ohm, and, consequendy, when such
cells are used for feeding track circuits, an external resistance
coil must be connected in series with the track battery to pre-
vent waste of energy and injury to the battery elements when
a train is on the track circuit. Similarly, in the alternating
current system, the transformer feeding the track has a com-
paratively low internal resistance, and either a resistance coil
or an impeda|ice coil must be inserted between the trans-
former and the track to cut down the short circuit current
when the track circuit is occupied; otherwise, the transformer
might seriously heat or bum up, due to the short circuit over-
load, particularly if a train were held on the track circuit for
several hours, due to a wait for orders, for eaxmple.

Such a resistance coil needs litde description; it consists
simply of a few turns ^f mre of high specific resistance and of
large enough current carrying capacity to carry the short circuit
current without heating. The impedance coil consists of a
few turns of heavy wire wound around an iron core; such a
coil has a high self-inductance, which serves to choke down
the heavyshort circuit current, which would flow with a train
in the block were no impedance coil in the circuit.

•

13. Selectionof Impedance or Resistance. The deci-
sion as to whether a resistance or an impedance is to be em-
ployed between the transformer and the track, on steam road
track circuits, depends on the type of track relay used. In
the case of a single element relay, either a resistance or an im-
pedance could be used, but the use of the latter is advisable,
for, even though it costs more than the simple resistance, the
extra cost will be compensated for by the power saved with
the impedance: it must be remembered that, when a current

76 ALTERNATING CURRENT SIGNALING.

- . i«i».

passes through a resistance, the entire voltag^e drop results in
an I^ R heating or power loss, as explsuned in Chapter 1 1 v^
whereas, with an impedance, the choking effect due to self-
induction causes a voltage drop in quadrature or 90° out o£
phase with the current, so that but little power is lost; in fact
the power factor of the impedance used in signal work is about
0.2, whereas, with a resistance, it is, of course, unity.

When two-element track relays are used, however, the ques-
tion is more complicated, as the phase relations between the
two elements must be considered, and the use of resistancir or
impedance between the transformer and the track will have
a bearing on these relations. In the great majority of cases-
met with on steam roads, an impedance is used, but no rule
can be set down. The decision rests on the result of the track:
circuit calculations described in Chapter XIII.

14. Bonding of Steam Road Track Circuits. For this*
purpose, any one of the following combinations, may be used:

(a) Two No. 8 B, W. C. galvanized iron bond wires;

(b) One No. 6 B. & S. geige semi-annealed solid cop-
per bond and one No. 8 B. W. G. iron bond.

The D. C. resistance of iron is about seven times that of
copper, and, when alternating current is used, this f-atio
is much greater, due to the fact that iron is magnedc, and,
therefore, an appreciable amount of power is continuously
lost; calculations show that, although combinations (b) or
(c) cost more than (a), their extra cost will be more than com-
pensated for by the power saved through their use. In tnost
cases, however, the use of two solid copper bonds would not
be justified, a^ the power saved thereby over that required
with combinations (b) or (c) would not pcy for the dxtra
copper.

ELECTRIC ROAD TRACK CIRCUITS.

15. Characteristics of Electric Road Track Circuits.

In general principle, electric road track circuits and dteam
road track circuits are identical, and save for the extra ap-
paratus required with the former to take care of the propul-
sion current* the elements of both types of track circuit are

ELEMENTS OF THE A. C. TRACK CIRCUIT. 77

— . — i .

the same. Electric road track circuits may be end fed or
center fed. and either single element relays or double elenlent
two or three-position relays may be chosen, for the same tea-
sons as govern their choice on steam road track circuits; of
course, such relays must be immune to the propulsion current,
and the reader is referred to Chapter IV for full descriptions
of the various types. Furthermore, limiting resistances or
impedances must be used between the transformer and the
track, as on steam road track circuits, due attention being
paid to phaise relations, when two element relays are used;
however, in the case of single rail track circuits, a resistance
is always used, as, due to the possible circulation of current
from the propulsion system, through the track transformer
and its short circuit current limiting auxiliary, an impedance
might be useless, because of the partial loss of its choking
effect consequent to the saturation of its iron core. Where
phase considerations do not dictate otherwise an impedance is
used on double rail circuits to save power. A detailed con-
sideration of electric road track circuits will be found in
Chapter V.

Here, the similarity between steam and electric road track
circuits ends, for, whereas in the case of the former the track
circuit may be completely isolated electrically from the abut-
ting track circuits by insulated joints in both rails, this course
cannot be followed on electric roads, as the propulsion cur-
rent, coming through the motors from the trolley or third
rail, must have a continuous electrical path over the running
rails from track circuit to track circuit, back to the negative
side of the power generator in the substation or powerhouse.
This difficulty may be solved through the use of either the
single rail track circuit, or the double rail track circuit with
balanced impedance bonds.

16. Single and Double Rail Track Circuits. In the

single rail scheme, the track circuits are isolated oil one side
only; that side, or rail, of the track in which the insulated
joint is placed is known as the block raiU which, of course, can-
not be used for propulsion purposes, while the other side or
rail of the track having no insulated joints and carr3ring the
propulsion current, is known as the return rail, as the propul-
sion current returns over it to the negative side of the power

78 ALTERNATING CURRENT SIGNALING.

generator; however » as explained at length in Chapter V, the
passage of the propulsion current over the return rail causes
a voltage drop, as a consequence of which a certain portion
of the propulsion current passes through the track relay and its
feeding transformer. If the block is very long, or if the pro-
pulsion current is very heavy, the track circuit apparatus
may be seriously injured by overheating. Furthermore, the
conductivity of the track propulsion return system is cut in
two, through the sacrifice of one of the ralt^ "^r signal pur-
poses.

In the case of the double rail track circuit, insulated joints are
placed in both sides of the circuit, and both rails are used to
carry the return propulsion current as well as the signaling
current; by the use of the so-called bcdanced impedance bonds,
the propulsion current passes from track circuit to track cir-
cuit, around the insulated joints, but the signal current may
not pass. See Chapter V.

17. Track Circuits for Roads Using A. C. Propulsion;
Frequency Relays. Where either single or double rail track
circuits are used on electric roads operating with direct cur-
rent propulsion, a track relay which is immune to direct cur-
rent, but which will work on alternating current, is, of course,
perfectly satisfactory. When, however, we encounter the
problem of track circuiting on electric roads employing alter-
nating current propulsion, it is evident that the ordinary al-
ternating current track relay is inadequate, as it might be
caused to falsely close its contacts with a train in the block,
due to leakage currents passing through it from the propul-
sion system. This difficulty is solved through the use of a
higher frequency for the signaling current than for the pro-
pulsion current, and the employment therewith of a track
relay which will pick up only when the higher frequency sig-
naling current passes through its energizing coils. Such a
relay is known as a frequency relay, and full descriptions of
the various types will be found in Chapter IV. In all other
respects, the track circuit apparatus for roads using A. C.
propulsion is the same as that used on roads using D. C.
propulsion, with the exception that in the former case the im-
pedance bonds may be smaller; see Chapter V.

CHAPTER IV.

RELAYS.

ALTERNATING CURRENT SIGNALING.

F«.3fr-Si.«laEJ<n

CHAPTER IV.

RELAYS. ^ ,

SINGLE ELEMENT VANE RELAY

1. Description. The vane relay is the simplest, the
most economical, and altogether the best of single element
relays; it was the first alternating current relay used for signaling
purposes, and its twelve years of development have brought
it to a high state of perfection. The standard vane relay
is shown in Fig. 36.

The detail design of the vane relay and its principal dimen-
sions are shown in Fig. 37, where the prime mover, the alum-
inum vane 2 actuates the contact spring bar 4, through link
3, both the vane 2 and the bar 4 turning on jewteled bearings.
The contact springs 8 are supported on insulating studs 16,
screwed into bar 4; the relay is here shown in the de-energized
position with back contact 8 closed, so that, when the vane
swings upward, this contact will be broken, and the front con-
tact on the other side of the bar closed. The magnetic field
structure 1 consists of a set of two coils, connected in series,
slipped over the legs of a horizontal C-shaped laminated mag-
net core, the vane swinging vertically in the air gap between
the ends of the C, as shown. When the coils are sufficiently
energized, the vane is pulled upward through the sur gap by
an electro-magnetic action, as will presently be explained; the
instant the coils are de-energized, the vane drops immediately
by gravity, the momentum of its downward motion being
taken up by a small fibre roller 13, which is caused to roll
uphill against gravity when struck by the vane. This pro-
tects the vane against jar and rebound, the same action on the
upward stroke being secured through a flexible front stop 1 1 .

2. Theory of the Vane Relay. When two circuits are
placed near each other, a current sent through one will, in
general, produce an appreciable magnetic flux throiigh the
other, some of the magnetic flux of the first circuit becoming
linked with the second. The circuits are said to possess mu-
tual inductance, and, by taking into account the principle
as Lenz's Law, it is ea^ to arrive at the general nature r

ALTERNATING CURRENT SIGNALING.

CONTACT EQUIPMBNT9.

4 tronts 2 backs

2 fronts

4 backa

4rront

B 0 backs

3 fronts

3 backs

3 fronts 2 backs

Fie. 37— Sinili Elcn

EQUIPMENT.

I a fi-onta QDly

84 ALTERNATING CURRENT SIGNALING.

results produced by mutual inductance when the first circuit
is supplied with an alternating current, and the second cir-
cuit, which contains no impressed e.m.f., is simply closed on
itself. According to Lenz*s Law, the current induced in any
circuit by a varying flux always opposes the changes in fli:x
which give rise to it; and the circuit in which the current is
induced is subject to mechanical forces tending to move the
circuit, so as to reduce the extent of the flux variations.

Let us now suppose that the first circuit is fixed and the sec-
ond movable. If we assume the two circuits to be parallel
to each other, the second circuit will be repelled by the first*
since the result of such motion would be to reduce the ampli-
tude of the flux variations. Thus, a ring of copper or alum-
inum slipped over a pole of an alternate-current electro-magnet
will be projected upwards as soon as a sufficiently strong cur-
rent is sent through the coil of the electro-magnet, and, if pro-
vided with suitable guides, the ring may even be kept floating
in^ the air above the electro-magnet, gravity being neutralized
by electro-magnetic repulsion.

If the second circuit is prevented from having motion of
translation, but is free to rotate about an axis, rotation will
take place until the plane of the second circuit is parallel to
the inducing field; for this is the position in which the flux
fluctuations are completely suppressed. Since action and re-
action are always equal and opposite, an equal and opposite
couple will be experienced by the first circuit. A coil of wire,
for example, conve3dng an alternating current will, when
pivoted or suspended in front of a sheet of metal, experience
a couple, tending to turn it into a position at right angles
to the conducting sheet.

The principles just explained find a practical application
in the vane relay, in which case an alternating current field
magnet is made to act on two secondary short-circuited cir-
cuits. Let us suppose that two rings of copper of the same
size are suspended parallel to, and nearly in contact with, each
other in the field pf such a magnet. The currents induced in
the rings by the alternating magnetic field will be nearly in
phase with each other, the rings being nearly in the same re-
gion of the field, so that there will be attraction between them,
since conductor3 conveying currents flowing in the same di-
rection attract each other. Let us now suppose that the

RELAYS.

CONDUCTING SHEET

rings are dispUced relative to each other, as in Fig. 39 (A), in
a direction parallel to their planes. In Fig. 39 (A)» the shaded
portion represents the pole of the alternating current electro-
magnet, which, for the sake of simplicity, is shown of circular
shape. The attraction between the rings will tend to pull
them into coincidence, and there will be a component of

stress in a direction paral*
lei to the planes of the
rings. Next, suppose one
of the rings to be replaced
by a conducting sheet ^i
metal, as in Fig. 39 (B),
in which the dotted .circle
shows the position 'of the
pole, and let the ring be
fixed, while the conduct-
ing sheet is free to move.
If the ring were removed,
then, by symmetry, it is
clear that the currents in-
duced in the conducting
sheet by the alternating
flux from the magnet pole
would (assuming the sheet
to be of large extent, so as
to project well beyond

Fig. 3»-Illu.trating Attraction Principle ^y^^ i^^ edges) foUoW

of Vane Relay . , i i •

circular paths having

their centers in the axis of the magnet. But, with the
ring in place, according to Lenz's Law the currents induced in
it give rise to a magnetic field in opposition to the main field,
and the result of this is to cause a shifting of the main mag-
netic flux (whose distribution with the ring removed would
be uniform) toward the right hand "unshaded" crescent-
shaped portion of the polar surface. But, with this shifting
of the flux, the currents induced in the conducting sheet will
also be shifted to the right, following the paths similar to that
roughly indicated by the dot and dash line. Now, the por-
tion of the conducting sheet forming the closed circuit indi-
cated by the dot and dash line and the ring will behave rela-
tively to each other in the manner of the two rings in Fig. 39

66 ALTERNATING CURRENT SIGNALING.

(A), and, since the ring is fixed, the sheet will move from right
to left — ^i. e., frc»n the unshaded to the shaded portion of the
magnetic pole. Since, however, the conducting sheet % con-
tinuous, as it moves successive portions of it come into the
position of the dot and dash line, and so the pull is maintained
and the motion is continuous.

In the vane relay, whose operating elements are illustrated
diagrammatically in Fig. 40, the aluminum vane is free to
rotate, and takes the place of the conducting sheet above
mentioned in connection with Fig. 39 (B). Around one-half
of each pole face is placed a "shading" coil or ferrule, consisting
of a simple heavy band of copper, which takes the place of the
fixed ring in Fig. 39 (B). Coil C and its laminated iron field core
constitute the alternating current electro-magnet, and cause
magnetic flux to induce currents in the aluminum vane, which
by the continuous attraction action described above, swings
lipward in the direction of the shaded pole faces (those sur-
rounded by the ferrules) when coil C is energized.

3. Characteristics of the Vane Relay; Where Used.

(a) The vane relay is partici-Jarly attractive from
the standpoint of design, because of its simplicity of construc-
tion, and the large mechanical clearances between all fixed
and moving parts; only a small portion of the vane is encloted
by the pole faces, and, as the large air gap is vertical, there is
litde possibility of the vane sticking to the field structure -be-
cause of foreign particles fcJling in the air gap. Furthei^*
more, all its parts, especially the air gap, are open to easy
inspection through the glass shield, without taking the rel^^jr
apart. -^

(b) From what has been said above in regard to its theoiy
of operation, it is evident that the relay will operate only on
alternating current. It is perfectly immune to direct current,
and is, therefore, suitable for use on electric roads using D.
C. propulsion, as well as on steam roads.

(c) It i» quick and positive in its action as the vane
shoots down by gravity immediately the relay is de-ener-
gized. It is, therefore, admirably suited for use on short
-lutomatic block track sections and detector circuits in inter-
ockings where quick shunting is indispensable; if a slow

•bunting relay were uied in tha former case, k train might
run through a considerable portion of the block before the
■ignal went to stop, and in the latter case, n switch might be
thrown under a train. In fact, the vane relay is the only one
which can be logicaHy used for such service.

(d) The single element vane relay, from the standpoint of
power, economy is not well suited for use on very long track cir-
cuits, because it is a single dementrelay.rec^ving all its power
over the rails, and cannot, consequently, equal the paws'
economy of two-element relays on long track circtiits. pardc-
ularly where the ballast is pool. Depending on ballast coa-
ditions, the
power economy
of the vane re-
lay will not
justify its use
on steam road
track circuits of

nominal length
of 2500 feet.
On electric
roads, with
double rail track
circuits, this
limit will be re-
duced to about
1500 feet, a* the
ngnaJing track
voltage must be
kept down to
the minimum to
keep the leakage current through the impedance bonds with-
in bounds; the operating voltage of the relay must, therefore,
be comparatively low, so that the current will be correspond-
ingly increased, in consequence of which the drc^ in the rails
is greater, and the limiting track circuit loigth is less than it
would be on a steam road ; of course the preceding limits are
not ironclad, because such variables as ballast, the impedance
of the bonds, etc., are important hctors. and cmly en actual
calculatioa of the track ciicuit power, carried out

F^i. 4a Operatuv EUment Vum RcUt.

8d ALTERNATING CURRENT SIGNALING.

^— ^^^^'^'^ ^ ■■■ ■ ■ ■ ■ ■— ■ ■ ■■ ■■■■■■, ■■ ■ , I —■■■■■MM , . , , ^

to the method described in Chapter XIII, will establish the
exact limit in track circuit length where a two-element relay
becomes more economical than a single element relay. The
above limits are simply convenient approximations applying
to average conditions.

(e) Having but one element, the vane relay here de-
scribed is a two-position relay, and cannot, consequendy, be
used for polarized track or line control.

On short track circuits on either steam or electric roads,
the vane relay will generally prove to be more economical
than a two-element relay because the latter is burdened with
the power required for its local winding, which latter power is
const£uit regardless of the length of track circuit. For this addi-
tional reason the vane relay is the best for use on detector
circuits or for single rail track circuit work on D. C. electric
roads where the track circuits are comparatively short.

4. Power Data — The curves shown in Figs. 4 1 , 42, 43
and 44 cover the approximate power required for the oper-
ation of both steam and double rail D. C. electric road track
circuits of various lengths employing single element vane
relays; for single rail track circuits on D. C. electric roads,
the same relay winding is employed as for steam road cir-
cuits (2.65^— 1 .5^0.56 PF on 25 cycles and 4.5^ 1 .5* 0.56 PF
opi 60 cycles) and after determining the amount of resistance
tc^ be inserted between the relay and the track and between
the transformer and the track to take care of the known
liropulsion drop, the power at the transformer -may be cal-
culated according to the method described in Chapter XI II.
It was by this method that the curves in Figs. 41 • 42, 43
^d 44 were determined.

ALTERNATING CURRENT SGNAUNG.

nr Cuma for 2S Cycle Sinflo Element Vua
« Double Rail End Fed D. C Elecuic
Road Tiock CinwU.

«t Curve, for 60 Cytle 3iD,le E

in Double Rul End Fed D. C. E

Road Tnck Ciicuiti.

ALTERNATING CURRENT SICNALINC.

Fl|. 45. tronlai Galvu

RELAYS. 93

THE IRONLESS GALVANOMETER RELAY.

1. Description. Of two-element relays, those working
on the galvanometer principle are, perhaps, the simplest and
most easily understood, and it is now proposed to describe
the construction and theory of operation of the well-known
Ironless Galvanometer Relay shown in Fig, 45.

The vital parts of this relay (Fig. 46) are the local coils I,'
and the armature or track element 2: the local coils 1 are
firmly secured to a brass supporting frame attached to the top
plate, while on jeweled pivots 27, armature 2 swings inside
the local coils as shown. The armature shaft carries a crank
at its left end, which is connected to an operating link 23.
actuating the bar 4, pivoted at 26, carrjdng the contact fingers
6. The detailed construction of the contact posts, with their
terminals and blocks, insulating them from the cast iron top
plate, will be evident from an inspection of Fig. 46, the relay
being in the de-energized position, ^vith the front contacts
open.

The armature consists of a comparatively few turns of
heavy wire formed, and then clampied to, but carefully in-
sulated from, a kind of swinging frame attached to the arma-
ture shaft; in order to secure a perfect balance, small adjust-
able counterweight nuts are provided on each side of the ^
frame. Current is lead into the armature coil from the track
terminals at the right of the front view, through the vertical
brass extension strips 23 and 24, to flexible copper spirals sol-
dered at their inner ends to the terminals of the armature
coil, these termineJ wires running along the right hand por-
tion of the armature shaft. The stationary local coils are
connected by vertical terminal leads to posts near the middle
of the top plate. The armature is prevented from striking
the local coils when it picks up, by stop screws 29.

2. Theory of Galvanometer Relay. The electrical prin-
ciple on which the galvanometer relay operates will be readily
grasped from a study of Fig. 48, which shows the local coils,
armature and operating mechanism, of a two-position relay
in simple diagram form. The local coils L are connected so
that when a current flows through them, msignetic fields of
the same instanteoieous direction as shown are created; it is a
fundamental fact that, whenever a current flows through a

ALTERNATING CURRENT SICNALINC.

CONTACT EQUIPMENTS.

4 frooM 0 backs I
2 fronts O backa |

4 fronts 4 backa

4 fronts 2 backs

D Irodw G^vinon

■ CONTACT BQUIPMBNT3.

CODt

acts each direction

cont

acts each direction

contaj;ta each direction

Fig. 47. Thn* Ponaoa ii

ALTERNATING CURRENT SIGNALING.

conductor, a magnetic field is created about that conductor,
and the direction of the magnetic flux circles about the con-
ductor can be predetermined by what is known as the "Cork-
screw Rule/' which states that, if the forward motion of a
corkscrew which results as it is turned in a clockwise direc-
tion is taken to represent the direction in which the
circuit is flowing in the conductor, then the magnet-
ic flux circles are circulating around the conductor in
the same direction as the corkscrew is being turned. Of

course, as the cork-
screw is backed out
of the cork, it has
to be turned coun-
ter-clockwise, and,
consequently, the
flux circles turn in
a counter-clockwise
direction when the
current is flowing
in the conductor in
the same direction
as the corkscrew is
being backed out.

The fields pro-
duced in the upper
and lower halves of
the local coils, are
of course, opposite
i n direction, b e
cause the currents
are flowing, say, ^ou^or^/ the observer in the top halves and au;ay
from the observer in the lower halves, due to the fact that the
current has to flow continuously in loop fashion around the
coils. When the current flows around armature A toward the
observer in the left hand side of the armature, a field is created
according to the Corkscrew Rule, which is in the same direc-
tion as the field in the top half of the left hand local coil, so
that cAiradion results and the left hand side of the armature
is pulled upward: the field in the lower half of the left hcmd
local coil is in opposition to the field created in the left hand
side of the armature^ so that repuUiQn results, and the arma-

Fig. 48. Magnetic Flux Relationshipa
Ironlesa Galvanometer Relay.

RELAYS.

ture 18 again thrust upward. By a similar process of reason-
ing, it vdll be found that the right hand side of the armature is
attracted toward the bottom half of the right hand local coil,
and is repelled from the top half of the same local coil. Of
course, the above directions in polarity hold only for one-
half of the alternating current period; however, during the sec-
c»id half of the period, when the current is reversed, it is re-
versed in all coils, and the same attractions and repulsions
result as before, so that there is a continuous torque tending
to turn the armature in a clockwise direction to close the con-
tacts, as shown in Fig, 48. When current ceases to flow in
the armature, the attractions and repulsions cease and coun-
terweight W acts, by gravity, to open the contacts.

It will be noted that by means of a pole changer, as shown
in Fig. 34, Chapter III, the direction of current in the relay
armature can be separately controlled, so that the magnetic
fields produced in the right and left hand sides of the arma-
ture may be reversed in direction, causing the armature to
swing in one direction or the other, as desired; it is to be
remembered that the pole changer does not reverse the cur-
rent in the local coils, as they are permanently connected to
their feeding transformer. Therefore, by means of a pole
changer, the currents in the track and local elements may be
placed in phase or 180 degrees out of phase, depending
on the position of the pole changer.

Fig. 49. Method of Counterweighting Three Position Relays.

This means that the relay may be caused to operate
in three positions, as shown in Fig. 49. In such a relay,
the armature lifts a counterweight, W, no matter which
^vay it swings; when the armature is de-energized; one or ,
the other of the counterweights causes the armature to return ,

98 ALTERNATING CURRENT SIGNALING.

to the horizoatal, or neutral, position, where all contacts are
open. Hius, the relay may be used for controlling home and
distant, or three-position, signals, without the use of line
wires for the distant, or caution, indication, as will be
gathered from Fig 34, Chapter 111.

It ought to be noted that the greatest turning force is ex-
erted on the armature, and the greatest pressure results on the
contacts only when the armature current and the local cur-
rent are either in phase or 180 degrees out of phase; then full
attraction or full repulsion occurs. With other phase rela-
tions, the torque on the armature falls off; for example, if the
armature and local currents were in quadrature, the armature
would not pick up, even with a heavy current flowing it in,
for there would be four times during each period when one or
the other of the two currents would be zero* while the other
were a maximum, under which conditions no torque would be
produced in the armature. It will be evident, therefore, that
it is highly important to approximate in practice as closely
as possible the ideal phase displacement of zero degrees or
180 degrees between track and local currents, if good pressure
on the contacts is to be obtained with a fair amount of power.

With only an alternating current flowing in the local coils
of the ironless galvanometer relay, foreign direct current in
the armature would not pick the armature up; the rapid re-
versals of the alternating magnetic field due to the local coils
would be too rapid for the armature to follow, it being of con-
stant polarity, due to the D. C. flowing through it. The relay
is consequendy immune to direct current.

3. Characteristics of the Ironless Galvanometer Re-
lay and Where it is Used, (a) Although the ironless gal-
vanometer relay is not so economical in power as some of the
other two-element relays, it is of a very simple rugged construc-
tion, and all its parts are in full view so that they can be readily
inspected. Furthermore, the mechanicsd clearances are large
and there are no air gaps to clog. Like the vane relay, many
thousan-s of these relays are in service and are giving excel-
lent results.

(b^ The relay is perfectly immune to direct current, and
hence is especially adapted for use on electric roads using
D. C. propulsion, as well as on steam roads. As it is a two-

element relay, it is intended for use on long track circuits,
where a single element relay would take too much power.

(c) From what has previously been said, it is evident thaf;
the gfJvanometer relay may be used as either a two-position
or a three-position relay.

4. Power Data. The curves shovm iu Fig«. 5(X-55 cover
the approximate track circuit power required for the oper-
ation of the ironless galvanometer relay oA both steam and
electric road track circuits of various lengths; the relay local
is of course fed separately, the power required by the local
being given in the heading of each diagram. The power data
given for the track element in each heajiiiig is based on the
track and local currents being in phase, but the track circuit
vector diagram, constructed as described in Chapter XIII
will in many cases indicate that when the relay is actually
operating under the given set of track circuit conditions, the
track and loced element currents are not exactly in phase;
hence the volteige and current at the track transformer must
be increased to compensate for this imperf^t phase rdation-
ship and the curves shown in Figs. 50-55 have been so correct-
ed so as to apply to actual conditions. For a full discussion of
this correction factor see Chapter XI I L

|06 ALTERNATING CURRENT SIGNALING.

■"

a.^lJ J™LII L.l«l 1.

^'^^^^!jU

-*,rf

_l ^

JUi"

»;

~i^T~

j^ 1

«•

«i<^

f^'

«•

:<^

f«

t:v

ALTERNATING CURRENT SICNALINC

Fla. a. Power Cur

104 ALTERNATING CURRENT SIGNALING.

Fif. K. Inm Cdvuwmeiei Rslay.

RELAYS. 105

THE IRON GALVANOMETER RELAY.

!• Description and Theory. Another important two«
element relay; known as the Iron Galvanometer Relay, is
illustrated in Figs. 56 and 57. This relay is exacdy the same
in principle as the Ironless Galvanometer Relay previously
described, and the constructive design of the two relays would
be very much the same» if it were not that an iron magnetic cir*
cuit is used in the Iron Galvanometer Relay. As with the
Ironless Galvanometer Relay, this relay operates most eco*
nomictdly when its track and local elements are exacdy in
phase or 180 degrees out of phase.

The 'inverted U-shaped iron field magnet is clearly shown
in the ^ectional side view of Fig. 57, where it will be seen that
the loctJ coils 1 and 2 are supported on the poles of the field
magnei; the local coils are connected in series. A cylindrical
iron core visible in the sectional back view is hung from the
field yoke down within the interior circular bore of the field
magnet, so that the hollow armature coil 3 may swing on its
pivots 24 in the air gap between the cylindrical core and the
field magnet. The contact bar 5 with its operating lever is
actuated from the armature through pin 29 carried on a bar
attache^ to the bottom of the armature shown in Fig. 57. ^

The object of using iron field cores is to make the relay more
economical in the way of power than a similar ironless relay,
as, of coiirse» a strong magnetic field can be produced with a
small energization of the local magnetizing coil when an iron
core is used. Due to the fact that the magnetic flux is rapidly
alternating in the cores, they are built up of thin sheets of steel
painted on both sides to prevent the alternating magnetic flux
from inducing heavy currents in the field structure, just as the
flux induces the operating currents in the vane of the vane
relay. These induced currents, known as eddy currents, tend
to flow, of course, at right angles to the direction in which the
flux is moving as per Fleming's Rule described inChapter II,
so that, if the field structure is built up of thin painted steel
stampings (known as laminations) , piled in the direction of the
armature shaft, the eddy currents cannot flow, because they
are of low voltage and the paint on the laminations is of com-
paratively high resistance. Practically all alternating cur-
rent apparatus is made up with laminated cores to save the

ALTCRNATINC CURRENT SICNALINC.

CONTACT EQUIPMKNT8,

Fig. 57. Two pDHIioa Ira

CONTACT EQUIPMENTS.

4 contacts

in each direction

3 coQtacts In each direction

2 contacts

in each dlrecUon

106 ALTERNATING CURRENT SIGNALING.

losses in power which would otherwise result from th^ heat-
ing due to the eddy currents. This statement applies not
only to the iron galvanometer relay, but to the vsme relay
as well.

2. Characteristics of the Iron Galvanometer Relay
and Where it is Used, (a) The iron galvanometer relay cai)
be made for operation in either two or three positions, and
is, therefore, adapted to polarized wireless signaling.

(b) Having an iron core, it is more economical than th<^
ironless galvonometer relay previously described, but due, to
the use of the iron core, the iron galvonometer relay is not
absolutely immune to very heavy direct currents under cer-
tain conditions. Consequently, it is intended for use only
on steam roads, where it has seen an extensive and success-
ful application.

3. Power Data. The curves shown in Figs. 59 and 60
cover the approximate track circuit power required for the
operation of the iron galvanometer relay; the relay local is of
course fed separately, the power required by the local being
given in the heading of each diagram. The power data given
for the track element in each heading is based on the track
and local element currents being in phase, but the track cir-
cuit vector diagram constructed as described in Chapter XIII,
will in many cases indicate that when the relay is actually
operating under the given set of track circuit conditions, the
track and local element currents are not exactly in phase;
hence the voltage and current at the track transformer must
be increased to compensate for this imperfect phase relation-
ship and the curves shown in Figs. 59 and 60 have been so
corrected so as to apply to actual conditions. For a full dis-
cussion of this correction factor see Chapter XIII.

;r Relay End F«d St«a

ncMT ReUy End Fed SiMm

ALTERNATING CURRENT SIGNAUNG.

Mwl<l 12 Polyphue Relay

MODEL 12 POLYPHASE RELAY.

). Description, Polyphase relays are. perhaps, the
mcist economical relays for track circuit work, although they
are characterised by a more dtlicate construction than the
vane and galvanometer relays previously described. Poly-
phase relays are o( the two-element type, with two sep-
arate and individual cchIs, wound, however, on the lanie
iron core and producing motion in a metal drum without
windingB, in much the same fashion as the vane in a vane te-
lay is caused to rotate; in fact, the metal drum of the poly-
phase relay corresponds exactly to the vane of the vane relay.
Th« outside laminated core, with its two windings, is known
as the ilalor and the metal drum is called the rolor. The
Model 1 2 polyphase relay is shown in Fig. 6 1 .

Its construction is shown in Figs. 62 and 63, the first of
v^ch shows the elements of the operating mechanism, and
the second the relay in detail. The case of the relay consists
of a rectangular front portion which houses the contact fin-
gers, operating gears and links, and supports the slate top
plate carrying the contact posts and terminols; cast integral
with the rectangular portion of the case is a cylindrical por-

Fi(. 62. Opantinc Mccbsnum Model J 2 Polypbus ReUy.

ALTERNATING CURREhfT StCNALING.

CONTACT EQUIPMENTa.

8 fronts 4 backs
6 fronts 4 backs
4 fronts 4 backs

10 fronts 0 backs
8 fronta 2 backs

6 fronM 2 backs

4 fronts 2 back8_

4 fronts 0 backs _
2 fronts 4 backs

2 fronta 2 backs

2 fronta 0 ba^ks

Fw- 63. Two-P<wii<m Model 12 Polypbua Rainy.

CONTACT KQDIPMENXa.

8 pos. 6 neg.

6 pos. 4 neg.

6 pos. 2 neg.

4 poB. 8 neg.

4 pos. 4 neg.

4 poa. 2 nt«.

8 poa. 4 neg.

8 POS. 2 nag.

10 poH. 2 nee.

2 poH. 6 nag.

2 POS. 4 nes.

2 poa. 3 neg.

This r^ay mtkY bJso be provided with contacts closed only in
de-energlzed position of the rolay; such a contact takes tlis u
as one complete tbrce-posltlon (poa. and neg.) contact.

Bb.M. ThlH-Pad

n M<xM 12 PoIypluHB RcUr.

114

ALTERNATING CURRENT SIGNALINa

tion at the back, which houses the motor operating mechan-
ism— that is. the stator and the rotor. The stator S, with its
coils, is shown assembled in the cylindrical portion of the case
in Fig. 62; the four terminals of the two stator coils are located
on the rectangular portion of the case just at the right of the
stator in Fig. 62, which also illustrates the metal drum or rotor
D, which turns in the air gap between the stator and central
laminated core K shown in cross section. The rotor is pivoted
at its closed end in a jeweled bearing 23, Fig. 63, carried by
the end plate of the stator case, while at its open end it is sup-
ported in a similar bearing carried by a stud projecting from
the rectangular portion of the case, also shown in the sectional
side view. Fig. 63. The right hand end of the rotor shaft carries
a small pinion P, Fig. 62, driving a segmehtal gear V, which
in turn operates the shaft carrying the contact fingers through
a crank and operating link 3, Fig. 63. One of the windings on
the stator is a local coil, which is, of course, continuously ener-
gized direcdy from a transformer or some other source of al-
ternating current power; the other element or winding is fed
from the track, and, when both elements are energized, the
rotor is caused to spin around so as to close the relay contacts
through the pinion, segmental gear and links above mentioned.
When the contacts are fully made, the rotor stalls, still main-
taining torque to keep the contacts closed. A counterweight
is attached to the shaft of the segmental gear, so that it drops
by gravity, causing the rotor to spin backward to open the
contacts when the relay is de-energized. As will presently
be explained, the relay can be made to operate in either two

or three positions,
as desired, depend-
ing on the direction
in which the rotor
is made to move.
The relay shown in
Fig. 63 is shown in
the de-enegized
position, with its
front contacts open.
2. Theory of
the Polyphase
Relay. Polyphase

INDUCED CURRENTS

Fig. 65. Metal Diac, Dragged around
by Inducdon.

RELAYS.

115

relays operate on what is known as the Induction Motor prin-
ciple, which will be understood from a consideration of Figs.65,
66 and 67. If, in the former drawing, the i>ermanent magnet P
is caused to revolve about the periphery of the metal disc D,
then the disc will be dragged around in the same direction in
"which the magnet is being moved. The motion of the metal
disc results because of the fact that the strong moving field,
due to the permanent magnet P, induces currents in the disc,
which themselves set up a field, reacting on the field of the
magnet in such a manner as to pull the disc toward the mov-
ing magnet. In other words, these mutual forces, accord-
ing to Lenz's Law, tend to diminish the relative motion of
magnet and disc; as the magnet is moved positively around
by hand, the disc, consequently, has to follow.

We must now consider how it is possible to induce such
currents in the metal drum, or rotor, of the polyphase relay
in such manner that a continuous turning effect will be pro-
duced by the mutual action between the rotor currents and
the field which causes them. Evidendy, it would be impos-
sible to obtain such a result with but one inducing current in
the stator, because the magnetic field produced thereby would
merely oscillate in direction along one line, and the field due
to the currents induced in the rotor would likewise oscillate
along the same line. If we can cause the current in the stator
coils to produce a field which, instead of oscillating along a
fixed line, always
oscillates along a
line which constant-
ly rotates around
the center, always
in the same direc-
tion, then the de-
sired result can be
obtained. Fortun-
ately, such a rotat-
ing field can be pro-
duced, if, instead of
a single stator wind-
ing, we employ two similar but distinct windings on the field,
taking care to supply these two elements with two alternating
currents of the same frequency, but differing in phase by a

Fig. 66. Quadrature Currents in
Poljrphase Relay.

116

ALTERNATING CURRENT SIGNALINa

quarter of a period, or 90 degrees, as shown in 'F^g. 66, where
it will be observed that, when one current A is at its maxi-
mum, the second current B is zero, and vice versa, while at
four points in a complete cycle they have equal numerical
values; at two of these points they are of the same sign,
either both positive, as at R, or both negative, as at T; in the
other two cases, they are of opposite sign, as at S and U.

We have now to show how much such currents cah, when
passed through two distinct windings, produce a rotating
magnetic field; Fig. 67 shows two windings in their simplest
form, AA representing, in section, a single coil or loop of
wire placed horizontally, and BB a similar coil fixed at right
angles thereto. A current passing through coil AA will pro-
duce a field in the vertical direction, as represented at XY,

while a similar cur-
^^ rent in ,coil BB will

set up a hori'^ontal
field RS. . Now,
what we heve to
consider £3 the
strength and direc-
tion of the resultant
field produced by
two coils, which
field will, of course,
be determined by
the relative values
of the respective
instantaneous cur-
rents in the two
coils, as shown in
Fig. 66. For example, when A is at its maximum and
B is zero, the field due to A may be represented in strength
and direction by line OC, and this is the resultant field, since
the current in B is then zero; 45 degrees later, as at R in Fig.
66, the two currents are equal. L«t 0£ in Fig. 67, drawn to
the same scale as OC, represent the field due to A; then the
equal line OD will represent the field produced by B. * Com-
plete the parallelogram and we obtain line OF, representing
the strength and direction of the resultant field at this instant.

Fig. 67. Illiistrating Production of Rotating
Magnetic Field.

RELAYS. Il7

^,_ ■ I . I .

In the same manner, we can find line OG, representing the
resultant field 45 degrees later still, when B is maximum and
A is zero. Obviously, the resultant field has rotated 90 de-
grees from the direction CX^ to the direction CXj, during a
quarter cycle, and. by proceeding further, we should find that
the resultant field rotates uniform]^ about point O, making
a complete revolution for every complete cycle of the currents
in the stator toils. OH, for example, corresponds to the time
S in Fig. 66. This rotating field induces current in the metal
drum, or rotor, of the polyphase relay and causes it to
rotate, just as the disc shown in Fig, 65 is dragged around by
the magnetic field of the moving permanent magnet. A study,
of Figs. 66 and 67 will make it evident that the rotor can be
dragged around^in one direction or the other, as desired, de-
pending on the\lime phase relation qf the currents in the track
and local winai^s; for example, if tlve track current lags 90
degrees behind the local current, j^e rotor will turn, say*/
clockwise, while, if, by means of a pol^ changer, as shown in
Fig. 34, Chapter III, the track current |s caused to lead the
local current by 90 degrees, the rotor would rotate counter-
clockwise. V The relay may, therefore, be made to operate in
either two or ^|^|iee positions. Furthermore, it will be noted
from Figs. 66!.atid 67, that the relay works best when its track
and local currents are in quadrature; if the two currents were
in phase, the magnetic field would not rotate at all, and the
contacts would not be closed, even if both elements were fully
energized. ■ Polyphase and galvanometer relays are, there-
fore, contrary in this respect, as the galvanometer works best
when the currents in the two elements are in phase. Of
course, the winding usually connected to the track could be
connected to a line, if necessary, so tl^t the relay could be used
for line work, in which case the line element would generally
be wound for 110 volts.

3. Characteristics of Model 12 Polyphase Relay and
Where it is Used, (a) In the matter of power consumption
this relay is the most economical of all relays.

^(b) It is absolutely immune to direct current, and may,
Aerefore, be used either on electric roads using D. C. propul-
tton, or on steam roads.

Iia ALTERNATING CURRENT SIGNALING.

„

1 II

■■'

.'/

i\ ,

'/#

jrw

„

vv^r.

—

ff Sff

^Jy

i/.-m

—,

-,.

,„

= J=te

■i

-s;

-r

,„ ^

-T7

W-

■,#-

Sg ^ «

^•^

^^^- ^

^^_ln £ '

LSSS^S^* ^1

-t-/'

^^P^iy?^

as?' '

-±_ -

|m™,,^~,^~. ^— j^-

•"««»&.^r,i(»r'™'

I20r ALTERNATING CURRENT SIGNALINa

is, consequently, ackipted to polarized wireless signaling, the
polarity of the track elemisAt in this latter case being controlled
by a pole changer fl(hif t6d by the signal mechanism, as sho^wn
i|i Fig. 34, Chapter III.

(d) Like all pol^ph^ie relays, the Model 12 relay is more
costly than simpler relays, siich as the galvanometer or vane,
dnd its construction i§ h^Hcessarily more delicate. With care-
f ul manufacture, however, polyphase relays can be depended
on to give excellent sehrice, and many thousands of them
are in use.

, 4. Power Data. The curves shown in Figs. 68-71 cover
the approximate track c^cuit power required for the oper-
ation of the Model 12 polyphase relay; the local element of
the relay is of course fed separately, the power required by
the local being given in the heading of each diagram. The
power data given for the track element in each heading is
based on the track and local element currents being in quad-
rature, but the track cirdiit vector diagram constructed as
described in Chapter XII 1, will in many cases indicate that
when the relay is actually Operating under the given set of
track circuit conditibns^ the track and local element currents
are not exactly in qii^rature; hence the voltage and current
of the track transformer mu^t be increased to compensate for
this imperfect relationship .jand the curves shown in Figs.
69-71 have been so corrtectc^ as to apply to actual conditions.
For full discussion of this correction factor see Chapter XIII.

ALTERNATING CURRENT SIGNALING.

FlK. n. Radical polypbiH Rail

RELAYS. 123

THE RADIAL POLYPHASE RELAY.

!• Description. Another very efHcient and compact
polyphase relay, illustrated in Figs. 72, 73 and 74, is known as
the Radial Type, and is characterized by a very ingenious ar-
rangement of the contact fingers and terminal posts. The
induction motor movement is housed at the right of the relay,
as illustrated in the sectional side view of Figs. 73 and 74.
The four termincJs for the track and local coils project from
thestator case, two on either side, as shown in the lower front
views 9f Figs. 73 and 74. The motor mechanism itself is exactly
similar to that of the Model 12 polyphase relay previously de-
scribed, but it operates through link 5, Figs. 73 and 74, a porce-
lain wheel 4, shown at the exact center of the upper front view;
this porcelain wheel is slotted, or toothed, as shown, and as it
rotates one way or the other, it moves the movable contact
members projecting in the slots in the wheel. The contact
members and terminal posts are carried on a large porcelain
ring, so that it is easy to secure a nice arrangement of con-
necting wires. It will be seen, from Fig. 72, that the contacts,
and many of the moving parts, are within full view, and the
back of the stator case is provided with glass windows to
allow inspection of the induction motor movement.

2. Theory of the Radial Polyphase Relay. The the-
ory on which this relay operates is exactly the same as that
of the Model 12 polyphase relay previously described.

3. Characteristics of the Radial Polyphase Relay and
Where It Is Used, (a) The induction motor movement of
the radial relay is smaller than that of the Model 12 polyphase
rday, and, as a consequence, the radial is somewhat less eco-
nomic in the way of power.

(b) Working on the induction rotor principle, the radial,
like the Model 1 2 polyphase relay, is absolutely immune to
direct currents, and is, consequently, suitable for use on elec-
tric roads using D. C. propulsion, or on steam roads.

IM ALTERNATlMd CURRENT SIGNAUNG.

CONTACT BQUIPMBNTS.

S troata 5 backs

to fronts 0 backt

« fMDta 2 buka

8 fronts 2 back!

Fi|. 73. Two-PMliaa [Udul PolnilkU* [UUr.

Thla relay ma; also be provided with contacts dosed onl; In the

. ,.„j 'tlon of the relay: such a contact '-■ — "■-

iletB three-poBltlon (poB, and aeg
CONTACT EQUIPMENTS.

dA-ener^zed position of too relay: such a contact takes the
(pace m one complete three-poBltlon (pos, and aeg.) contact.

la I^dial Pulypbuc Rel«y

126 ALTERNATING CURRENT SIGNALING.

suitable for use with the polarized wireless ccmtrol system il-
lustrated in Fig. 34, Chapter III.

(d) The arrangement of binding posts of the radial relay
is preferred by some to that of the Model 1 2 relay.

4. Power Data. The curves shown in Figs. 75-76 cover
the appronmate track circuit power required for the opera-
tion of the Radial Polyphase relay; the relay local is of course
fed separately, the power required ^y the local being given in
the heading of each diagram. . The^«|^wer data given for the
track element in each heading is based' on the track and local
element currents being in quadrature, but the track circuit
vector diagram constructed as described in Chapter XIII, will
n many cases indicate that when the relay is actually oper-
ating under the given set of track circuit conditions, the track
and local element currents are not exactly in quadrature;
hence the voltage and current of the track transformer must
be increased to compensate for this imperfect relationship
and the curves shown in Figs. 75-76 have been so corrected so
as to apply to actual conditions. For a full discussion of this
correction factor see Chapter XIII.

RELAYS.

127

leac

4000 6COO MOO /OOOO /fOOO f^OOO

isjvsrff or r/tACft cfftcuiT /n rcer

/6000 /OOOO ^oooo

Fig* 75. Power Curves 60 Cycle Radial Polyphase Relay End Fed Steam

Road Track Circuit.

a eooo 4000 €000 ai^o /oooo ifooo /^oo /tooo /aooo iocoo
itMsrft of^ f/fACK c/^co/r /Ai reer

Fig. 76. Power Curves 25 Cycle Radial Polyphase Relay on End Fed
Double Rail D. C. Electric Road Track Circuit.

ALTERNATING CURRENT SIGNALING.

CantrifuEAl Fivquency ReUy.

REIAYS.

129

THE CENTRIFUGAL FREQUENCY RELAY

1. Function. The characteristic feature of track cir-
cuit apparatus for electric roads employing alternating cur-
rent for propulsion purposes is the track relay. Thus far, all
the alternating current roads in this country employ a pro-
pulsion current having a frequency of 25 cycles. Differentia-
tion between the propulsion current and the signaling cur-
rent is secured by using a higher frequency for signaling than
for propulsion; a 60 cycle current is now quite generally used
for signaling purposes. The track relay must, therefore, be
immune, not only to direct current (for foreign direct currents
leaking from adjacent D. C. interurban trolley roads must be
guarded against, as on many steam roads), but, in addition,
it must be able to select between the 25 cycle propulsion cur-
rent and the 60 cycle signaling current, closing its contacts
only on the latter.

2. Description of the Centrifugal Frequency Relay.
This relay, shown in Fig. 11 ^ has an induction motor move-
ment consisting of a metal shell rotor A, Fig. 78, rotating in-
side a wire
wound stator B,
because of the
rotating mag-
netic field pro-
duced in the
stator by . two
windings carry-
ing currents in
quadrature. In
fact, the motor
portion of the
centrifugal re-
lay is exactly
similar to that
of the polyphase
induction motor
relays previous-
ly described, and is, of course, immune to direct current.

The shell rotor A, Fig. 78, is integral with a Y shaped metal

Fig. 78. Operating Mechanism Centrifugal
Frequency Relay.

ALTERNATING CURRENT SIGNALIh4G.

CONTACT EQUIPMENTS.

10 fronta 0 backs 8 IrtmtB 4 backs

6 froDtB 0 backs 4 fronts' 2 backs

4 fronts 0 backs

Fit. J9. Cotiihiiiil FnqoH

RELAYS. 131

yoke C, carrying at E the juvots of the ball centrifuges D,
which, at their upper end F. engage in a slot in the sliding
collar G. When the rotor of the relay is running, the ball
centrifuges are thrown outward at their lower ends D, swing-
ing about points E to pull the collar G downward; this
collar is attached, through a ball bearing, to a link H hooked
to the contact operating bar J pivoted at K.

3. Theory of the Centrifugal Frequency Relay. The
centrifuge arms and collar above mentioned work on the same
well known principle as the ball governor of a steam engine.
7*he speed at which an induction motor operates in revolutions
per second is equal to twice the frequency of the currents flow-
ing in the stator windings, divided by the total number of poles
of the stator. Now, the stator winding of this relay is com-
posed of two elements, so that the relay may be either a single
or double element relay, as required; in the single element re-
lay, the currents in the two windings are displaced in phase
by such artificial means as resistance or reactance in either
winding, while, in a two element relay having separate track
and local coils, proper phase displacement between the track
and local current is secured by the use of a reactance between
the transformer and the track. In any event, one element
of the vrinding is always connected to the track, so that leak-
age 25 cycle current from the propulsion system might enter
the relay. Due to the fact, however, that the speed at which
the rotor operates varies with the frequency, the centrifuge
arms will not fly out so far on 25 cycle propulsion current as
they will on 60 cycle signaling current, and it is by utilization
of this characteristic that the relay is made selective between
propulsion and signaling currents. The centrifuge member
is designed so that on 25 cycles the balls will not fly out far
enough to lift the operating collar sufficiently to close the con-
tacts. On 60 cycles, however, due to the fact that the speed
is over double what it is on 25 cycles, the centrifuge balls fly
out much further and the contacts dose. It will be seen,
therefore, that, even on a ^o element relay, where 25 cycle
propulsion current might not only circulate through the track
element, due to unbalancing (see Chapter V), but might also
reach the local coil, on account of being stepped up into the
transmission ^stem by the track transformers as a result of

132 ALTERNATING CURRENT SIGNALING.

* ' ■ ^

unbalancing, the relay is still immune to the propulsion current,
because the speed of the rotor will not be sufficient to close
the contacts of the relay. For these reasons, the relay is
truly selective between the propulsion and signaling currents.
The operating movement of the relay, therefore, runs con-
tinuously. When a train enters the track circuit, the track
element of the relay is short circuited, and the relay starts to
slow down. Due to momentum, however, the moving ele-
ment has a tendency to keep rotating for a time, particularly
because it runs on ball bearings. Were it not for a braking
arrangement, the relay would be very sluggish in opening its
contacts. TTiis braking arrangement consists of a magnetic
brake M (Fig. 78), actuating an armature N, carrying a brake
pad O, which engages with the brake disc L carried by the
rotating element of the relay. The coils of the magnetic
brake are connected in series with the track element of the
relay, so that, when there is no train on the track circuit the
full operating current flows through the track winding of the
stator and the brake coil in series, energizing the brake coil
so as to lift the brake pad O to free the disc L. The moment
a train enters the track circuit, current ceases flowing through
the brake coil and track element of the relay, and the brake
pad engages the disc, bringing the rotor to a stop, so that the
contacts are opened in about one-quarter of a second after
the track circuit is shunted. The brake is shown clearly at
the right of Fig. 77.

4. Characteristics of the Centrifugal Frequency Relay
and Where it is Used, (a) The contacts are never closed,
unless the rotor is running at the propter speed, as determined
by the frequency of the signaling current. Hence, if. for any
reason, the rotor is jammed, the centrifuge balls drop by grav-
ity, and the contacts are opened. This is an important safety
feature.

(b) Even as a single element relay, the centrifugal type is
the more economical than any other frequency typ)e now on
the market. As a two element relay, it possesses the well
known economy characteristics of all two element relays, in
that only a small amount of power need be transmitted over
the track.

RELAYS. 133

(c) It is, of course, distinctly a two-position relay, and per-
fect broken down insulation joint protection may be secured
when it is used as a two element relay, by staggering polarities
on opposite sides of the insulation joints, so that direofeion of
rotation of the induction motor movement will be reversed in
case both insulation joints break down. To prevent the con-
tacts being closed if the rotor reverses its direction of move-
ment, the rotating collar G, Fig. 78, operated by the centrifuge
arms, is provided on its periphery with ratchet teeth en-
gaging in one direction with a thin spring pawl when the relay
is de-energized. When the rotor moves in the proper direc-
tion, the spring pawl simply slides over the ratchet teeth on
the collar G at pick-up, but, as the collar is raised as the cen-
trifuge arms speed up, the ratchet teeth are lifted out of en-
gagement with the spring, and this slight element of friction
is, therefore, eliminated when the relay operates at full nor-
mal speed. When the relay is wound for single element work,
the direction of rotation of the induction motor movement
never changes, and, of course, the ratchet is then useless: in
other words, as a single element relay, the centrifugal type
does not atford broken down joint insulation protection, which,
however, may be said of all other relays of the single element
type.

It will be evident from the above description that the oper-
ating element of the relay rotates continuously, and to those
familiar with only D. C. relays for steam roads* a question will
no doubt arise as to whether the bearings of the relay and
other moving parts are not liable to wear out. Such would
very probably be the case if a great deal of care were not used
to provide the rotating movement with a fine set of ball bear-
ings, which are almost fricrionless and will wear indefinitely,
because the weight of the ojDerating movement is purposely
reduced to a minimum, so as to make the weight on the bear-
ings very slight. On account of its safety and power economy,
this relay has generally superseded the vane type frequency
relay next described, except in the case of electric detector
circuits in interlockings.

5. Power Data. The curves shown in Fig. 80 cover
the approximate track circuit power required for the oper-
ation of the Centrifugal Frequency Relay: the relay local is of

134 ALTERNATING CURRENT SIGNALINC:.

courte fed Mporatdy, the power required by the local being
given in the beading o( the diagram. The power data given
for the track dement ■■ based on the track and local element
cuiTcnts being in quadrature, but the track circuit vector
diagiam constructed aa described in Chapter XIII, will in
many case* indicate that when the relay is actually operating
under the given set of track circuit condition), the track and
local dement currents are not exactly in quadrature; hence
the vcJtage and current of the track transformer must be
increased to compensate for this imperfect relationship and
the curves shown in Fig. 60 have been so corrected as to
apply to actual conditions. For a full discusuon of this cor-
rection factor aee Chapter XIII.

Fl«. Sa Poww CuiVM Ccntrifossl Frcqaency Rdmy on Double Rail Eul
F*d Trvk Cinuit, Sinsl* Truk A. C. Electric Ro»l.

The winding and power data given in Fig. 80 apply to a
relay primarily intended for a single track road. Where a
multiple track road is to be signaled and the tracks are cross
boikded.a special winding must be provided if adequate broken
rail protection is to be secured. The track element for this
•pecial winding takes 0.35 volts — 4.8 amperes at 0.65 P. F.
and the local wiikding takes 0. 1 ampere at 1 .0 P.F. on 1 10 volts.

(J6 ALTERNATING CURREhJT StCNALINC

Fig. ai. Vuic Frequency Relay.

RELAYS. 137

THE VANE FREQUENCY RELAY.

1. Description. The essential elements of tKig relay,
illustrated in Fig. 81, are a laminated H-shaped iron core,
carrying magnetizing coils, energized from the track, which
induce currents in a moving vane, operating the front con-
tact 1 0, through a link 4, as shown in Fig. 82, the relay here
being shown in the de-energized position, with the back con-
tacts closed. The vertical legs of the H-shaped iron core I,
Fig. 83, are bent inwards to enclose the vane V, which is cut
out in the middle, so as to not interfere with the middle leg
of the H-shaped core. This middle leg carries the magnet-
izing coils TT connected in series and receiving energy from
the track. All four bent-in legs of the H-shaped core arepar-
tially surrounded by copper ferrules F, which split the mag-
netic flux and cause the vane to be dragged upward toward
the ferrules by a rotating magnetic field, just as in the case
of the ordinary single element vane relay described previous**
ly. The vane, therefore, is acted upon by two opposing
forces, since the two sets of ferrules at opposite ends of the
core are both trying to make both ends of the vane rotate
upward about its axis PP.

2. Theory of the Vane Frequency Relay. At the left
end of the core, however, the air gap in which the van0 swings,
is greater than that at the right end, and this tends to cut down
the flux, and consequently, the upward pull on the left half of
the vane. The main portions of the legs of the right half of
the core are surrounded by copper ferrules CC, which choke
back the flux somewhat in that part of the core, so that, in
turn, the upward drag on the right half of the vane is dimin-
ished. The air gap at the left end of the core, and the fer-
rules CC on the right half of the core, are so proportional that
when 25 cycle propulsion current flows in coils TT, the up-
ward pulls on the opposite ends of the Vane will just be equal,
and, of course, opposite, so that the resultant torqu^ exerted
on the vane is zero; the vane is counterweigh ted, however, to
rest on a back stop, keeping the front contacts open. Now,
when 60 cycle signaling current flows through the coils TT. the
above balance is destroyed, for, whereas the reluctance of
the left hand air gap remains unchanged, the choking effect
of the ferrules CC is greatly increased so that the greater

138 ALTERNATING CURRENl SICNALINI

CONTACT EQUIPMENTS.

* fronts 2 backs

2 fronts 2 backs

4 RvDtB 0 backs

3 fronts 0 backs

2 rronts 0 backs

Fv.8Z. Vuw Fn^uucy Rd.y

RELAYS.

139

Fig. 83. Operating Element Vane
Frequency Relay.

part of the flux flows through the left half ^^ the iQore; tificler
these circumstances, the upward pull on tlie left half of the
vane is the greater than the pull on the jright hand half, and
the vane is dragged upwards on the left hand end to close the
relay contacts. The torque effects created in the two ends of

the vane by the 25
cycle propulsioncur-
rent are always bal-
anced; this balance
is destroyed on 60
cycles so that the
relay can close its
contacts on the high
frequency signaling
current. Such a
relay is, therefore,
immune to direct
current and to the
alternating propul-
sion current.

3. Characteristics of the Vane Frequency Relay and
Where it is Used, (a) Vane type frequency relays possess
the advantage of simplicity, but they naturally can be wound
only as single element relays. Due to this fact, they are not
as economical of power as Centrifugal Frequency relays and
are nowadays used principally on short track circuits, as, for
example, in electric detector circuit work, to which they
are well fitted by their quick action.

4. Power Data. The curves shown in Fig. 84 cover the
approximate power required for the operation of the vane fre-
quency relay on an end fed single rail track circuit on a four
track road. In making up the curves sufficient resistance
has been inserted between the relay and the track and be-
tween the transformer and the track to take care of a propul-
sion drop of 1 5 volts per 500 ft. of trt^ck circuit. £>epending
upon the number of tracks and the distance of the trolley
above them the impedance of the rail circuit is variable and
the reader is referred to the series of tests made on the New
York, New Haven & Hartford under the direction of Messrs.
Scott and Copley and described in the 1906 Proceedings of
the A. I. E. E, •

140

ALTERNATING CURRENT /SIGNALING.

30
28
£6
24
ZZ
ZO

1 J 1 i 1 1 1 1 1 1 1 1 1 1 1 1

y^ia fll£Otf£NCY RkLAY-A C £ucnf/ClfOAD-€0 CYCL£ Sia CVKJlElfT

ITTc.

(DWCV

•lay

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r-o.

*5A-

'0.»^

'/?/

Ctrc

lit f

'/•

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wm^

fiat

.tot

rtjr^

•^

Vott^

^jgsati-

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.ittu-f Circuit Amps

Mot

A Ct

ciijfi

A/or

mal Amp

% Bti

>cA <

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100

200
j.£j>fSTH or

300 400

T/TACK cjiecu/r tN r££T

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2
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300

Fig. 84.

Power Curves Vane Frequency Relay on Single Rail End
Fed Track Circuit A. C. Electric Road.

CHAPTER V.

TRACK CIRCUITING ON ELECTRIC ROADS

CHAPTER V.

TRACK CIRCUITING ON ELECTRIC ROADS.

General Considerations. Perhaps the most interesting
application of cJtemating currents in railway signaling occurs
in their use on the track circuits of roads using electric propul'
sion. Tliis in a way may be considered as the general or broad-
est case of the A. C. track circuit, for here we meet with all the
problems usually encountered in the steam road A. C. track
circuit, and, in addition, are forced to provide an electrically
continuous return path for the propulsion current from track
circuit to track circuit, while still, in a signaling sense, preserv-
ing between adjacent track circuits the insulation essential
for their individuality. At first glance, these requirements
seem paradoxical, cmd, in fact, a considerable amount of in-*
venting and experimenting was done before a successful solu-
tion of the problem was arrived at. It is the object of this
chapter to describe the present day methods employed in the
track circuiting of roads using electric propulsion, whether
direct or alternating.

TWIHD WAIL OH THOLLEY WIRE^

Fig. 85. Illustrating Effect of Propulsion Drop.

Tlieir immunity to direct current has been the prime factor
in bringing A. C. track circuits into extensive use on steam
roads, while their simplicity and economy in maintenance has,
incidentally, added to the attractiveness of this system. On
electric roads, the employment of A. C. track circuits is im-
perative» as will be evident from a study of Fig. 85, where it
will be noted that the ccmtinuity of the upper rail has been
maintained for the return of the propulsion current back to
the negative side of the main power generator G, the lower
rail being cut and insulated for track circuit signaling pur«
poses: vdth this arrangement, there is a voltage drop all the

144 ALTERNATING CURRENT SIGNALING.

m^^mmm^^ i ' ■ ■■ . .M ■■■ ii ■ ■ i ■ ■ ■ ■ i i ■ . ■iiiijfc

way along the continuous return rail, proportional to the
strength of the propulsion current and the resistance of the
return rail, this latter quantity depending, of course, on the
weight of the rail and the length of the track circuit. With a
train at B, traveling in the direction of the arrow, a voltmeter V,
connected as shown, will, therefore, in the case of a direct
current road, indicate a considerable D. C. drop, and this
drop will appear directly across terminals A and C of the
track relay X, since there is a low resistance connection over
the lower rail and the axle of the train between points B and
C. If a direct current track relay were used, it would pick
up, even with a train in the block, providing the above drop
in the return rail due to the propulsion current were high
enough. This can be guarded against, first, by making the
track circuits short and by increasing the carrying capacity
of the return, either by bonding the return rail to an elevated
structure, when the latter is available, or by providing a heavy
cab[e in multiple with the return rail, both of which expedi-
ents will diminish the resistance of the return, and, second, by
arranging the polarities of the signaling current and the pro-
pulsion current in opposition, so that, if a polarized track re-
lay is used, the relay will be caused to close its contacts when
signaling current flows through its coils, but will open its con-
tacts with an excess of propulsion current. Even, with a
polarized relay, however, the direct current track circuit
scheme leaves much to be desired, because the direction of
the propulsion current may vary, due to a change in the dis-
tribution of the load, depending on the geographical location
of the trains in relation to the power house. Altogether,
therefore, the direct current track circuit is limited in its scope
and is not fitted for use on electric roads. On the other hand,
alternating current track circuits using relays of the vane,
galvanometer, or induction motor type, are absolutely im-
mune to direct current, regardless of both its volume and di-
rection. Such relays respond only to alternating current and
are inherently strictly selective. Alternating current track
circuits have, therefore, come into general use everywhere on
electric roads.

ELECTRIC ROAD TRACK CIRCUITS. 145

SINGLE RAIL TRACK CIRCUITS FOR DIRECT

CURRENT ROADS.

1. Description and Theory. The first and simplest
scheme involving a division of a road into independent track
circuits, while still providing an unbroken return path for the
propulsion current, is the single rail return track circuit illus-
trated in Fig. 86, where it will be noticed that the upper rail
provides a continuous path for the return current to the
power generator G, the lower rail being blocked off by insula-

THIRO RAIL OR TROLLEr WIRE-^

Fig. 86. Single Rail A. C. Track Circuit.

tion joints into sections for signaling purposes. Depending
TSpon the volume of the propulsion current in the continuous
rail, as well as upon its resistance and the length of the track
circuit, a certain D. C. voltage will be impressed across the
terminals of the A. C. track relay X, as explained in connec-
tion with Fig. 83, and even when there is no train in the
block, as for example in Fig. 86, a direct current will still flow
through not only the relay, but also through the secondary
coil of the track transformer T. This results from the fact
that the transformer secondary, the lower or block rail and
the relay coil in series constitute a multiple path for the pro-
pulsion current around the return rail between A and the
point where the transformer is connected to the return rail.
The strength of the direct current flowing through the relay
and transformer will, of course, follow Ohm*s Law, varying
directly with the D. C. propulsion drop between the above
points on the return rail, and inversely with the sum of the
resistances of the relay and transformer secondary with their

146 ALTERNATING CURRENT SIGNALING.

track leads, together with the complete rail circuit connect-
ing relay and transformer.

The direct current thus caused to flow through the relay
and transformer secondary in no way affects the safety of the
track circuit, because the relays (vane, galvanometer, or in-
duction motor type) are purposely designed to respond only
to alternating current, as explained in Chapter IV. It is
immediately apparent though, that while the relay and trans-
former secondary may have a high impedance or choking
effect on the signaling current because of its alternating char-
acter, tH^ ohmic resistance to a steady direct current may
easily be quite low; consequendy, if some means are not pro-
vided to cut down the direct current flowing from the return
rail, th^ relay and the transformer may actually bum up.
Aside ^qm this, however, is the fact that the laminated iron
cores of both relay and transformer may be highly magnetized
by the direct current flowing through the coils. If sufficient
direct current flows through the transformer secondary, its
core may be magnetically saturated, with the result that the
impedance df the primary coil falls, and an excessive current
is drawn from the signal transmission line. As for the relays,
tho80 of the vane and induction motor type would likely be
sluggish in their movements, due to the damping effect of the
heaVy direct current field, while those of the galvanometer
type would likely chatter badly.

2. Liniiting Resistances and Impedances. The most
apparent way to limit the strength of the direct current flow-
ing through the relay and transformer secondary is to insert
resistance in the circtdt, and this is quite generally done.
Tlie typical case illustrated in Fig. 86 shows resistances Ri
and R2 inserted between the relay and the track, and between
the transformer and track respectively. In the case of short
track circuits of 200 feet or 300 feet in length, where only
relatively small currents of say 1000 amperes flow in the pro-
pulsion rail, resistances Ri and R2 may be simple tubes of
the proper capacity, as shown in Fig. 135, page 221, but on
heavy traction roads, such, for example, as the Interborough
Rapid Transit, where the currents in the propulsion rail may
run as high as 3000 amperes and the track circuits are nearly
1000 feet long, heavy cast iron grids of gieat ladiating

ELECTRIC ROAD TRACK CIRCUITS. M7

^» I ■ I ■ 11 ■ ■ ■ ' ■ ■— ■■■ ■ ■ ■ ■ ■■ .^-— ■■■■ ■ — ■■■ii.i»

pacity such 88 that shown in Fig. 144, page 237, must be em-
plpyed in both the transformer and relay circuits. In the
case of the transformer, of course, the series resistance R2 not
only serves to cut down the direct current, but in addition
limits the short circuit A. C. signaling current with a train on
the track circuit.

In very heavy propulsion systems the track relay may be
still further protected by the use of an impedance coil Fig. 141,
page 233, connected across the track terminals of the relay,
as shown at Z in Fig. 86; this coil, which consists simply of a
few turns of heavy wire wound arpund a laminated iron core,
has a dead or ohmic resistance mufli less than that of the re-
lay coil, so that the impedance coil^acts as a by-pass to shunt
the larger part of the direct propulsion current out of the re-
lay, the alternating signaling current being choked back out
of Z, due to the latter's self-induction.

Impedances, consisting of a coil of wire wound on an iron
core, are never used on single rail track circuits for D. C. elec-
tric roads to limit the short circuitffjcurrent flowing from the
transformer to the track with a train in the block, as is the ease
on steam road track circuits. From what has already been said
regarding transformers for single rail Work it will be realized
that the magnetizing action of the direct current flowing from
the return rail because of the propulsion drop would saturate
the iron core of an impedance, and* then the reactance or
choking feature of the impedance Would be lost; the ohmic
resistance of the coil would then constitute the only limit on
the transformer short circuit current. For this reason, a
simple resistance is always used on single rail track circuits for
D. C. electric roads.

3. Transformers for Single Rail Track Circuits. To
guard against the core of the track transformer becoming
saturated due to the passage of propulsion current through its
secondary, it is customary to provide an air gap in the mag-
netic circuit; such transformers are generally used on single
rail track circuits, particularly on D. C. electric roads, and
are known as open magnetic circuit transformers. They are
fully described in Chapter VI.

4. Relays for Single Rail Tracl^ Circuits. While any of
the usual A. C* relays, the vane, ironless galvanometer or

148 ALTERNATING CURRENT SIGNALING.

polyphase induction motor type, may be used in connection
with single rail track circuits, the general practice has been to
use the vane, because of its simplicity and relatively high econ-
omy on short track circuits to which the single rail scheme in
generally limitedl

In some cases, where the propulsion current in the return
rail is not too heavy and the track circuit is not too long, the
relay may be wound to such a high resistance that no external
limiting resistance will be required between the relay and the
track as at Ri, Fig. 86. In the case of the detector circuits
in the Pennsylvania New York terminal it was found possible
to follow this scheme; here, however, the propulsion drop in the
return rail amounted to only 4.5 volts D. C. On the other
hand, in the New York Subway (Interurban Rapid Transit),
a propulsion drop of 22 volts D. C. had to be allowed for, the
track circuits being longer than in the case of the Pennsylvania,
and both resistance Ri and impedance Z, Fig. 66, had to be
used to protect the relay.

5. Characteristics of Single Rail Track Circuits and
Where They are Used. Single rail track circuits may be
used wherever one of the running rails can be given up for
signaling purposes. This may be a sacrifice, however, on
heavy traction roads, especially where there is no elevated
structure to be bonded -to as an auxiliary return, and the
power department of the road is likely to object to single rail
circuits because of the increased drop in the return system.
On the other hand, there are many cases where single rail
track circuits may be used and still have sufficient return ca-
pacity for the propulsion system, as, for example, in inter-
lockings, where many return rails may be bonded together.

Granted that one of the rails may be given up for propul-
sion purposes, the signal engineer may make his single rail
track circuits just as long as the propulsion drop will permit.
The first thing to be determined, then, is the exact amount
of propulsion current to be taken care of, so that, knowing
the resistance of the rail, the propulsion drop per hundred
feet of continuous rail may be calculated. Knowing just
what D. C. voltage the track relay and transformer can stand
(taking into account if necessary the limiting resistances and
shunt impedance above described)* it is then a simple matter

ELECTRIC ROAD TRACK CIRCUITS. 149

to determine the maximum permissible length of single rail
track circuit. Theoretically, of course, relays, resistances,
transformers, etc., might be designed to work on any length
of track circuit, but practically a limiting length is reached,
ivhich, if passed involves excessive power losses in the resist-
ances and very expensive track circuit apparatus generally.
This is a matter which should receive the joint attention of
the signal engineer of the road and the company manufactur-
ing the apparatus.

On account of their relative simplicity and adaptability to
fouling protection and complicated track circuit layouts
through switches, single rail track circuits find their
broadest application in interlockings and terminals, where
due to the shortness of the track circuits, the propul-
sion drop limitation is not a factor. Here the double rail
system, next described, requiring impedance bonds and in-
sulation joints in both rails, is apt to be very cumbersome.
Under such circumstances, the single rail track circuit has
the important advantages of low first cost, simplicity in ap-
paratus, and economy in power, besides its marked suitability
to interlocking layouts. Practically all detector circuits are
consequently of the single rail type.

In conclusion, it is to be noted that, while satisfactory
broken rail protection is provided by single rail track circuits
used on a single track line (with an isolated continuous re-
turn rail), where, if either the block rail or the continuous re-
turn rail were to break, the relay would open its contacts,
equal protection is not afforded where single rail track cir-
cuits are employed on a double or multiple track road where
the continuous rails are all cross bonded together, for in this
latter case if the continuous rail on the track were to break,
the relay on that track circuit might still be picked up with a
train in the block, due to the fact that the break in the con-
tinuous rail would be bridged around by the cross bonding and
the continuous rails on the other track or tracks, as the case
may be; these remarks also apply of course to a single track
line where the continuous rail is bonded to an elevated struc-
ture or to any other such auxiliary return.

150

ALTERNATING CURRENT SIGNALING.

DOUBLE RAIL TRACK CIRCUITS FOR DIRECT CUR-
RENT ROADS.

1. Description. On account of the limitations of single
rail track circuits previously discussed and to permit of both
rails of a track being utilized for power returns purposes, the
double rail track circuit shown in Fig. 87 was devised. As
above suggested, this involves insulating both rails of abut-
ting track circuits from each other in a signaling sense, and
the novel feature of the double rail track circuit is the so
called impedance bond B instsdled in the track circuit, as
shown in Fig. 87, to provide a path for the propulsion current
from track circuit to track circuit back to the negative side

ARROWS SHOW DIRECTION

OF PROPULSION CURRENT

THROUGH IMPEDANCE BONDS

ARROWS SHOW INSTANTANEOUS
DIRECTION OF AC LEAK THROUOH
IMPEDANCE BOND^

PROPULSION CURRENT

SIGNAL TRANSMISSION LINE

Fig. 87. Elements of the Double Rail Track Circuit.

of the power generator. These are called bonds because they
are low resistance connectors between adjacent track circuits,
and they are impedance bonds because they impede, or choke
back, the flow of A. C. signaling current from one rail to the
other of the same track circuit across which they are
connected.

2. Theory of Impedance Bonds. In principle, the im-
pedance bond consists of a laminated iron core provided with
two heavy copper windings wound in opposite directions and
so connected, as shown at the left of Fig. 87, that the mag-
netizihg action of the direct propulsion current in one-half
of the winding is opposite to that of the other half of the
winding, under which circumstances, if there are the same
number of turns and amperes in each winding, the magnetiz-
ing forces will balance or neutralize each other and no mag-
netic flux will flow in the iron core. Now, while the propul-

ELECTRIC ROAD TRACK CrRCUITS.

sion current divides up in multiple through the oppodtdy
wound halves of the bond, the A. C. signaling potential
across the rails tends to force an A- C. current through the
two windings in leriei and not in oppaaiiion, so that the full
impedance oi both halves of the bond is present to choke back
the flowof signalingcurrentfromXtoYacrossthe track. At
first glance this statement may DotseemtoBgree with what haa
been previously said regarding the balancing action of tbe
propulsion currant,
but this balancing
action results only
from the fact that
the two ctAla are
wound in opposite
directions, starting
from the outer rail
terminals X and Y
from which the pro-
pulsion currents enter
the bond, leaving it
at the middle ptAnt
M, known as the
neulral terminal of
the bond. The sig-
naling current, how-
ever, tends to flow
fromX toY. through
bothccnls.in thesame
direction, as shown at
the right of Fig. 87,
the direction of the
propulsion current
being shown at the

left of the same (igurei of course, both the propulsion current
and the signaling current flow simultaneously through the
bond windings. Four separate impedance bonds are shown
in Fig. 87^two at each end of the track circuit. Each set of
bonds are jointed across their middle or neutral points M by
a heavy cable known as the neulral conntdlan. which serves
to carry the propulsion current from one track circuit to the
other through the bonds.

Fig. as. Illultiotini LmCion nl ImpsdaDC*
Bond* in t>u! Tnck. New York

152 ALTERNATING CURRENT SIGNALING.

Were it not for their choking effect, the bonds would act
as a short circuit across the track circuit, and indeed at all
times they allow a certain amount of signaling current to leak
from one rail to the other, depending on the A. C. voltage
and the impedance of the bonds between rail terminals. While
the windings necessarily have a very low ohmic resistance to
allow the direct propulsion current to pass easily, the im-
pedance to the A. C. leak across track is generally many hun-
dred times the ohmic resistance, due to the fact that the bond
has an iron core. With a perfect neutralization of the D. C.
magnetizing forces due to the balancing action just described,
the core presents a high permeability to the flux produced by
the A. C. signaling current, which would not be the case if the
core were saturated by the D. C. flux.

3. Unbalancing. With perfect bonding of the rails in a
double rail track circuit, the resistance of both complete rail
conductors of the track circuit should be the same, so that the
propulsion current would divide equally between the rails;
then the currents in the two windings of the bond would be
equal and the bond would be perfectly balanced with no D. C.
flux in the core. This ideal condition cannot always be as-
sured, however, because with a loose or broken rail bond any
where in the track circuit the resistance of that side of the re^
turn will be increased and less current will flow in that rail
than in the other, with the result that the magnetizing action
of one-half of the bond will be more than that of the opposing
half, under which circumstances the balance will be upset.
The difference between the direct current in the halves of the
bond is known as the unhalancing current and its action is to
magnetize the iron core; this lowers the permeability of thecore,
with a consequent decrease in the impedance to the leakage of
A. C. signaling current through the bond. With a heavy unbal-
ancing current, the core might actually become saturated
with D. C. flux, in which case the impedance of the bond would
be destroyed. To prevent this, most bonds are made with
an air gap in the iron core so that the iron is not £ipt to be-
come saturated with the direct current flux. By the same
token, of course, the A. C. impedance of the bond is lowered,
due to the high reluctance of the air gaps. Therefore, a bond
'th an air gap will allow a greater amount of A. C. signal ng

ELECTRIC ROAD TRACK CIRCUITS.

153

current to leak through it than would be the case of a bond
without an air gap in its magnetic circuit; but, whereas the
former allows greater A. C. leakage, it is comparatively free
from the action of unbalancing current, which cannot be said
of the bond without air gap, whose impedance may be com-
pletely ruined by a comparatively small amount of unbal'
ancing. Fig. 89 shows the unbalancing curves for a bond
capable of carrying 2000 amperes propulsion current per rail,
the air gap being 5-64 inch; the abscissa (horizontals) show
the D. C. unbalancing in amperes, while the ordinates (ver-
ticals) indicate the amount of 25 cycle signaling current,
which will leak through the bond with voltages as indicated
on the various curves. It will be noted that the impedance
of the bond is
practically con-
stant up to
about 700 am-
peres unbeJan-
cing, particular-
ly on the lower
voltage curved.
It is the general
practice to de-
sign bonds to
handle 20 per
cent, unbalan-
cing, without a

serious decrease in the impedance; that is, the difference
of the currents in the rails shall not exceed 20 per cent, of
their sum.

z
o

50
45
40

g£30

t-<20

<2l5
M

6
<

2 VOLTS

1.2 VOLTS

_ _

—

■

—

.0 nvnix<cJ

1..^

— ■

60 240 400 560 720 660 1040
160 320 460 640 600 960 1120
O.CAMPERES UNBALANCING

Fig. 89. Unbalancing Curves for a 2000 Amp.
Impedance Bond.

Money is saved at the coal pile when the rail bonding of
an electric road is kept in good condition, for, not only arc
losses avoided in the propulsion return, but the wasteful leak-
age of the alternating current through the impedance bonds,
resulting from unbalancing, is eliminated. If the rail bond-
ing becomes so bad that the unbalancing capacity of the
bonds is passed, so much A. C. signaling current leaks through
the bonds that the relay does not receive sufficient current to
keep it picked up, in which case, of course, the signal goes to
danger, even with no train in the block.

ALTERNATING CURRENT SlCNALtNa

4. Imped&nce Bond Conatruction. A good idea of
the actual conatruction of large capacity impedance bonds
may be aecured from Fig. 90, where it will be seen that the
iron laminadons ate built up into a. shell type core around
heavy copper coila componng the winding. The copper i«
bare, but adjacent turns are prevented from touching each
other by wooden or fibre stripe employed as spacers. The
two tenninale projecting to the right at the top are connected
tofether in the Snished bond to form the neutral point M, in
Fig. 67. while the other two atrapa projecting at the sides are
the rail terminals shown at X and Y in F^. 87. The air gap
between the two parts of the iron core, employed to prevent
■aturation following unbalancing, 'is distinctly visible as a
^ horizontal white

line on the front
' face of thecore;

of course, there

gap in the back
leg of the core,
as well as in the
middle leg pro-
jecting down
' through the coil;

pected with a

shell type con-
struction. This particular bond has a capacity of 1500
amperes per rail. Its ohmic resistance (each half from rail
to neutral point) is 0.00043 ohms, and its impedance to a 60
cycle signaling current is 0.21 ohms, the unbalancing capB'
dty being about 700 amperes: on 25 cycles, the impedance
would be in proportion, or 0.08S ohms.

The core, complete with its coils and insulation, is enclosed
in an iron case fUled, sometimea with oil, but better, with
pttrolafum, a vaseline compound which is not only an ex-
cdlent insulator and protects the windings from moisture,
but is a aolid which cannot be forced out like oil in ca
bond i« flooded with water, aa acmietiines happens o

t the

ELECTRIC ROAD TRACK CIRCUITS.

tracks. Fig. 91 show* two btwids of the Fig. 90 type. encIoMd
in ihar cases, and installed in a track circuit, the neutral con-
nection between bonds being plainly visible at the left as tvn>
heavy ct^pet cables connected in multiple. This type of
bond, having a

capacity of
about 1300
amperes per
rail, is suitable
for the heaviest
trunk line ser-
vice: (or short
intervals it
will, of course,
handle several

mal 1500 am-
pere capacity.
On interurban
lines, the ser-
vice is not so
heavy, and,
conseq uen dy ,

F«. 92. Track Layout of Two Inururbu Roul li

156

ALTERNATING CURRENT SIGNALING.

the currents in the rails are less — in most cases normally
not over 500 amperes per rail; here, then, smaller bonds
may be used, as illustrated in Fig. 92.

5. Cross Bonding. Cross bonding between tracks is ef-
fected by connecting the neutral points of the bonds, as at
A, B and C, in Fig. 93. The negative return connection to
a power house, or substation, should always be made from the
neutral point of a bond inserted, if necessary, in a track cir-
cuit, as at E, in Fig. 93; preferably, however, the negative re-
turn should be connected to the neutral point of one of the
bonds at the end of a track circuit, if the location of the power
house will allow of this, as it is undesirable to insert an extra
bond in the midst of a track circuit, not only on account of
the cost of the bond, but particularly because of the extra
leak it constitutes in the track circuit. Short stub sidings.

f-*-

4-*

yj"?

THIRD RAIL OR TROLLEY WIRE

Fig. 93. Methods of Cross-Bonding, Insulating and Bonding of Sidings,
and Making Return Connection to Power House.

used merely for car storage purposes, may be insulated as at
D, Fig. 93, for even if their is considerable unbalancing with
a train beyond the insulation joint J on a short siding, the
main line switch would be reversed an3rway, opening the sig-
nal control circuit and throwing the signal to danger, regard-
less of the effect of unbalancing on the bonds, and the conse-
quent reduction of voltage on the track relay. Again, if the
fouling point on siding D is dose to point C, at the end of the
track circuit on the main line, two joints, instead of one, may
be placed in the siding at fouling point, the return cur-
rent from the rails out of the fouling back of the joints being
carried by a cross bond to neutral point C, both of the rails in
the siding back of the joints in the dead section being bonded
together; with such an arrangement, of course, unbalancing
of the main line track circuit will be avoided. Finally, where

ELECTRIC ROAD TRACK CIRCUITS. 157

there is considerable traffic on a long siding, and there is no
main line neutral p>oint C at hand, then a single impedance
bond may be installed, as shown on the spur track F, where
the neutral point of the bond is connected to both dead rails
beyond the insulation joints in the spur.

6. Relays for Double Rail Track Circuits on D. C*
Electric Roads. Vane, galvanometer, or induction motor,
relays (see Chapter IV), are used on double rail track circuits
just as on steam or single rail electric road track circuits; in
order to keep down the leakage of A. C. signaling current
across track through the impedance bonds, however, it is de-
sirable to use a comparatively low A. C. voltage on the track,
and. therefore, relays for double rail track circuits are always
wound for a low voltage, and a proportionately higher current;
otherwise, these relays are exactly the same as the steam road
relays.

7. Transformers, Resistances and Innpedances for
Double Rail Track Circuits on D. C. Electric Roads.
Either adjustable filler or constant potential track transform-
ers (sec Chapter VI) may be used, but they must have a
greater capacity than steam road track transformers, because
the electric road transformers must be large enough to supply
the current leaking through the bonds, in addition to that re-
quired for the relay. Due to the fact that there is little or no D.
C. propulsion drop to guard against, as in single rail track cir-
cuits, impedances with iron cores may be used, when required,
between the transformer and the track, to limit the short
circuit current with a train on the track circuit. Either a
simple resistance coil or an impedance may be used between
the transformer and the track, on vane relay track circuits,
because phas^ relations are of no importance in the case of a
single element relay like the vane; the use of an impedance,
however, is advisable, as it is more economical in power, be-
cause, whereas the drop through the impedance is almost
wattless, the drop through a dead resistance is wasted in heat-
ing. With the galvanometer relay, impedance is generally
required between the transformer and the track to bring the
track current in phase with the current in the local. The in-
duction motor or polyphase relay, on the other hand, gener-

I5d ALTERNATING CURRENT StCNAUNG.

-Ill -_■_-.— -■ ■ — -^^»

ally works best with a reol^tance between the transformer and
the track, because this type of relay is most economical of
power i^en its track and local currents are in quadrature.
For a description of the various resistances and impedances
in standard use, see Chapter VI 1; for a full discussion of the
factors governing their selection see Chapter XI IL

8. Characteristics of Double Rail Circuits. As has
been pointed out. single rail track circuits are limited in their
length ]>y D. C. propulsion drop, but no such restriction holds
with dovble rail circuits; for this reason the double rail cir^
cuit is particularly adapted for heavy electric traction, and
there are many cases where 10,000-ft. end fed, and 25,000-ft.
center fed, double rail circuits are being successfully oper-
ated. Adequate broken rail protection can be insured with
this type of track circuit. Finally, double rail track circuits
are veiTy stable, and not so liable to be atfected by variations
in ballast leakage; this stability results because the imped-
ance bei&ds connected across track are of such low resistance,
as compared with the ballast, that changes in the value of
the latter are not of much influence on the track circuit as a
whole.

9. Standard Bonds and Layouts for D. C. Electric
Roads. At the end of this chapter, a number of plates will be
found, showing the standard bonds used in direct current
propulsion work, together with drawings showing how they
may be set and connected into the track.

TRACK CIRCUITING ON ELECTRIC ROADS USING

A. C. PROPULSION.

1. General Scheme and Relays Used. The character-
istic feature of track circuit apparatus for electric roads using
alternating current propulsion is the track relay. Thus far,
all the alternating current roads in this country employ a pro-
pulsion frequency of 25 cycles. Differentiation between the
propulsion current and the signaling current is secured by
using a higher frequency foi- signaling than for propulsion;
a 60 cycle current is now generally used for signaling pur-
poses under such circumstances. The track relay must.

ELECTRIC ROAD TRACK CIRCUITS. IS9

tkerefore, be immune, not only tx> direct current (for (otcign
currents leaking from adj&cent D. C. interurban roods are
not tmuMnmon), but in addititm, it must be able to select be-
tween the 25 cycle pr^nilaitai current «ik<l the 60 cycle sif['
naling current Either the Centrifugal Frequency rdny or
the Vane Frequency rday, both of which are fully described
in Chapter IV, fulfill these requirements.

2. Single Rail Track Circuits on A. C. Propulsion
Road*. Oq altemBting curroit roads, as well as on Bleam
rDeda and lines using direct current propulsion, short single
rail track drcuits are used through interlockings for detector
circuit work, and the vane type frequency relay is generally
used for this purpose, because of its ciceedinBly rapid action.
Here, as in all cases where the single rail scheme is used, the
length of the track circuit is limited by the A. C. pr^>ul-
don drop in the return rail,'ai(d, in laying out the tmck dr-
cuits, care must be talun so that this drop is itot sufficient to

160 ALTERNATING CURRENT SIGNALING.

to cause an injurious heating current to pass through the re^
lays and transformers.

3. Double Rail Track Circuits and Impedance Bonds
for A. C. Propulsion Roads. In all cases where the track
circuits are of considerable length, as in automatic block sig'
nal territory, double rail track circuits are used, and, for this
service, the centrifugal type relay is generally employed, for
reasons of power economy. The impedance bonds for double
rail track circuits, on roads using alternating current pro-
pulsion, employ the same principle of magnetic balancing as
characterizes the bonds for direct current roads, for, althouj^h
the propulsion current is of an alternating character, still it is
divided up, presumably equal, between the two opposing
windings of the bonds, so that the alternating magneto-motive
forces are equal and opposite, and hence neutralize each other.
The iron core of tlie bond remains, therefore, unmagnetized,
so that it offers a high permeability to the magneto-motive
force generated by the alternating signaling current flowing
through the two coils in series, as prevoiusly explained in con-
nection with the bonds for direct current propulsion.

The principle claim made for the alternating current sys-
tem of propulsion is that it dispenses with rotary converters
and other auxiliary apparatus required in the direct current
system of propulsion to translate the alternating current en-
ergy received from the main transmission line to direct cur-
rent for propulsion purposes. Rotary converters are not
suitable for voltages much over 1 200 or 1 500 volts, and there-
fore, the trolley, or third rail must be of considerable con-
ductivity, because of the heavy current being carried. This
does not apply to the alternating current systems, as trans-
formers can be built nowadays for almost any voltage, so
that 1 1 ,000 yolts is now generally used for propulsion on A.
C. roads. With such high voltages, the propulsion currents
themselves are very small, and, therefore, the impedance
bonds do not have to carry so much current, and are much
smaller than on D. C. roads. As a matter of fact, the current
per rail on most alternating current propulsion systems gen-
erally will not run over 75 or 100 amperes per rail nor-
mally, which is only about 5 per cent, of the current used on
heavy traction D. C. systems.

ELECTRIC ROAD TRACK CIRCUITS. 161

^■^^■^^-^^■^^^^B '— ■ ■■■■-—— ■ —-■ 11 ■ ■ .1 ■■ I ■■■—■II. - ■»

Impedance bonds for roads using alternating current pro-
pulsion are, therefore, much smalW than would be the case if
direct current were used; as a matter of fact, it is often found
practicable to place two of these small bonds.one above the
other, in the same iron case, which makes the bond layout con-
necting two adjacent track circuits rather simple. One of these
double bonds, with the two cores and their windings housed
in the same case, is shown in Fig. 98; a novel feature of this
type of boiid is that the iron case itself serves as a neutral
connection between the two parts of the bond, the neutral
terminals of both windings being simply bolted to the case.
Hence, in this tyi>e of bond, only four terminals project outside
of the case. It will be noted, from Fig. 98. that the copper
winding is wound flat-wise, like an oblong roll of ribbon; the
copper forming each winding is bare, but adjacent turns are
separated from each other by a fibre ribbon wound between
the turns. Of course, the windings themsdves are very care-
fully insulated from the iron core.

4. Unbalancing. Unbalancing troubles are rare on
roads using alternating current propulsion, not only because
the propulsion currents themselves are small in volume, but
especially because, if more current flows in one-half of the
bond than the other, the half winding can^nng the heavier cur-
rent induces a voltage in the weaker half, tendihg to pull a
larger current through that weaker half. Thus, an a!Uto-
matic action exists, which tends to keep the bond well bal-
anced. For this reason, the bonds are not liable to be unbal-
anced, and no air gap is required in the magnetic circuit to
prevent saturation of the core, which would otherwise occur.

5* Standard Bonds and Layouts for A. C. Electric
Roads. At the end of this chapter, a number of plates will be
found showing the standard bonds used on electric roads using
A. C. propulsion, together with drawings showing how the
bonds may be set and connected in the track.

ALTERNATING CURRENT SINALING.

CHABAOTBBI8TI03.

sSSs 1 1-"»'"™-° I

D. O.

■»o 1 ,., 1

Hf. 9J. ImpKluca Bondfo

ELECTRIC ROAD TRACK CIRCUITS.

CHARACTERISTICS.

PropuWon

«S& 1 ■«•■■"»'<■■■

D. C.

1500 100

Fi|.M. Impeds,^

>r D. C PmputBuq

ALTERNATING CURRENT SICNALtNG.

CHARACTERISTICS.

Amps, per Rali

Layout Fig. No.

tS:

i§s

102.103

Fic.97. iDiMcUumBaiulrcirD. C.a

ELECTRIC ROAD TRACK CIRCUITS.

CHARAOTEBiariCS.

Oapodtv

°»sSvr'

tST

A. C.
A. O.

2:3 obl^

iSS

Flf. 90. D«blaln|Mdu«B«idtci(A. CPmnMso.

ALTERNATING CURRENT SIGNALING.

CHABACTERISTICS.

Capadtj

Amps, per rail

60 cycles Fig. No.

tS:

lO.Oohms 'iSlmihrt.
2,30hraa | Fii. 106

Fli. 99. Sioils Impsduica Bond far A, C. Piopul^on.

ELECTRIC ROAD TRACK CIRCUITS.

Fif. 100. Doubls Layout [or 1500 Amp, Bond. Rt. 96: tba

Two Bonda SLown Above are Provided with s

Sheet-lion Cover loi Piotection Agabut

Dragging Cu RiggiDg.

n .GG nn

sni^m

ig. 101. Double Layout for [500 Amp. Bond. Fig. 95; ttis T

Bond. Shown Abovs an Provided with s Sheet-Iron Cav«

for ProtvcdoD Agaiut DiaggiDg Car Rigging.

I6S ALTERNATING CURRENr SICNAUMC.

Fif. 101. Doubla Layunt fer 500 Ami). BobcI Fi(. 97. tn Tlua Layaut

tht Ntuttfel Couwction Batwaui Booda i* Mul« Lone Esoosh to

EUddmu tb* NKOvty «f Cutlinf the Rail* to Maka

Csmpan WiA F«. 103,

ELECTRIC ROAD TRACK CIRCUITS.

Fit. IM. Sio^e L>y«it for 500 Amp. Boad Re. 97 Fd, Uh .t th. End

oE Truk Ciicuiud Territory. Tt» Siiwte Leul >t ihs Rifkl

ConnecU to Nini'tiack Ciicuiud Roul.

—

Pif. No. 105. Sinile Layoul far 500 Amr

it i> Deadnd to Maka ConnBIioB i

CioM Bond (o ■ SwiKl

.d FIs. 97 F« Uh «

IK ALTERNATING CURRENT SICNALINC.

□ID

Fig. 106. LiytnicfDi Double Band Shown in R«.9B. The R>il Cbl.

■re Soldered et Tfacir Bond Endx Into Eye Conaeeton BlAud

to the Bond Tenruualei the Rul Endi of the Cable*

■R> Soldered to U-duped Dnnectoi.

Futeued >t Each End la the

Rul by Chunel Pin*.

CHAPTER VI.

TRANSFORMERS.

CHAPTER VI
TRANSFORMERS

1* General* Transformers fulfill the same function in
alternating current signaling systems as do the batteries in
direct current systems; that is, power is dravoi from the trans-
formers or batteries for the operation of the track circuits and
signals. Line transformers are those which supply the rela-
tively high voltage, generally 53 or 110 volts, best suited to
the operation of signal motors and slots. Track Transformers,
supplying lower voltages of from 5 to 15 volts, feed the track
circuits. In broad theory and general construction, all trans-
formers, whether line or track, are the same, and the present
chapter will, therefore, be devoted to a description of the
theory and construction of transformers as used in signal
work.

When it is desired to convey power over a transmi^tiio^ line
from a power house to some distant point, the wires ought to
be made as small as possible to save money in copper. At the
same time, the power lost in the transmission must not be
large if the system is to be economical. The power loss in
a transmission line is I^ R, the square of the current flowing in
the wires multiplied by their total resistance. The electric
transmission of a given amount of power can be made through
the use of a large current at a small voltage, or by a small cur-
rent at a proportionately higher voltage. In the first case,
large and expensive copper wires would have to be used if the
I^ R loss is to be kept within reasonable bounds. In the sec-
ond case, comparatively small and inexpensive transmission
wires may be employed. It is therefore necessary in the inter-
est of economy to use high voltages in the long distance trans-
mission of power. In alternating current signal systems, the
power is generally conveyed at 2200 volts or higher over the
transmission. Of course, it would be out of the question to
utilize such a high voltage directly on signal motors, relays,
and the like, not only because of insulation difficulties, but
especially because of the personal danger element. There-
fore, means must be provided along the line to transform the
power from the high electro-motive force and small current to
a low electro-motive force and proportionately higher current.

174 ALTERNATING CURRENT SIGNALING

* ' ■ ' ■ «»

The transfoi^iner fulfills this function. It does not generate
power; it merely changes the power h-om one voltage to
another.

2. Elements. The transformer in its simplest form con-
sists of two.^eparate tfnd distinct coils of wire wound around
the same iron core as^hown in Fig. 107. The cx>il which re-
ceives alternating curi'ent at the original voltage from some
outside source is Jcnpwn as the primary coil. . The coil which
delivers power from-.the transformer is known as the second-
ary coil. The- transfer of power from the primary to the sec-
ondary takes place tjtrough the medium of the magnetic flux

produced in the iron ring
by the alternating cur-
rent flowing in the pri-
mary coil; this flux, bong
consequently of an al-
ternating character, ris-
ing, falling, and chang-

Fig.107. Elcmento^ the Transformer. '^^ direction, cuts the

turns of wire composing
the secondary and induces an electro-motive force in the
secondary coil. The voltage induced in the secondary coil
depends on the rateat' which the flux lines cut the secon-
dary turns, and can .]be calculated once the frequency, total
flux, and number of t^ms are known.

3. Step-up and Step-down Transformers; Ratio of
Transformation. A step-up transformer is one which re-
ceives power at ^ low voltage and delivers it at a higher volt-
age; in this case, of course, the primary voltage is lower than
that of the secondary. Step-up transformers are used for ex-
ample, in power houses to transform the low voltage of the
generators up to the high voltage of the transmission. Step'
down transformers receive power at a .lajg^h voltage and de-
liver it at a low voltage; such transformers are located out
along the transmission line to transform the high transmis-
sion voltage to a low one for feeding track circuits, signals
etc. The ratio of tranrformation is the ratio of the primary
voltage to the secondary voltage; thus a transformer with a
2200 volt primary and a 110 volt secondary has a 20 to I
ratio.

TRANSFORMERS.

175

THEORY OF TRANSFORMER

4. No Load* When the secondary of a transformer is on
open circuit, no current is, of course^ flowing in that coil,
under which condition the transformer is said to be operating at
no load. The primary coil receives some current from the
mains, hovreyer, and the flux resulting from the magnetizing
action of the primary, rapidly alternating with frequency*
cuts both primary and secondary coils, inducing a voltage in
each of them as a consequence. The voltage induced in the
primary coil is opposite in direction and very nearly equal in
magnitude to the voltage impressed on the primary by the
supplying circuit. In other words, the primary circuit is
highly inductive so that only a litde current flows into the
primary from the mains because of this choking action; the
small current which flows is proportional to the difference
between the voltage Ei impressed on the .primary and the
voltage ei, induced in the primary coil-by its own flux.

These relations will be more clearly understood from a study
of the vector diagram (A) at the left of Fig. 108, covering an
ideal transformer — one whose iron core is so perfect that no loss-
es are produced

m It, one m
which the ohmic
resistance of
both primary
and secondary
coils is negligi-
bly small, and
finally one
whose primary
and . secondary
coils are so in-
terlaced with
one another
that all the flux
which links with
one also links
with the other

so 'that there is no magnetic leakage. Of
flux generiated in the iron core of such «

(A)

(»

I te,

Fig. 1C8. Vector Diagrams of TnuMfomiflr
Wo king on No Load.

course, the
transformer

176 ALTERNATING CURRENT SIGNALING.

varies periodically and accompanies in phase the mag-
netisiiig current which produces it. It is also fundamental
that the voltages induced in the primary and secondary coils
by the changing flux must lag 90 degrees behind the flux be-
cause it is when the flux is changing most rapidly at the zero
point of the sine curve that the induced voltage is the greatest.
These relations are illustrated by the diagram (A) at the left
of Fig. 108, where ei and E^ are the voltages induced ill the
primary and secondary coils respectively, by the flux caused
to flow in the iron core of the transformer by the primary
magnetizing current M, itself proportional to the difference
betwieen Ei, the voltage impressed on the primary by the
mains, and ei, the primary induced counter ^.m.f. These
relations hold for an ideal transformer working at no load.
In an actual transformer, however, the periodical alter*
nating magnetic flux causes certain losses in the iron core
which manifest themselves in heating. These losses, known
as iron losses, consist first of the hysteresis loss spent n
overcoming the friction between the molecules of iron as
they move backward and forward with the changes in the di-
rection of the flux, and second of eddy current loss spent in the
heating action of the currents induced in the iron core by the
varying flux. The eddy currents are in phase with the in-
duced voltages producing them, and, of course, these voltages
lag 90 degrees behind the flux, so that the corresponding op-
posite voltages and currents which must be supplied to the
primary to compensate for the iron loss are 90 degrees ahead
of the flux. Therefore, an iron loss component MIq must be
added to the magnetizing current OM shown vectorially in dia-
gram (B) at the right of Fig. 1 08, where the total primary no
load current is represented by OIq. The two components OM
and MIq cannot be added arithmetically, as they are not in
phase; they must be added geometrically as shown, in the
same manner as two forces are combined by the well-known
parallelogram of forces.

5. Loaded. When the secondary of a transformer is on
open circuit, no current flows through that coil. but. of course,
full voltage is generated in it by the alternating flux. The
instant the secondary circuit is closed, current flows in the

TRANSFORMERS. 1 77

secondary and then the transformer is said to be loaded. The
direction t>f the secondary current is, of course, opposite to
that of the primary current, and, consequently, the magnetiz-
ing action of the secondary current opposes and neutralizes
Xo a certain degree the flux produced by the primary, so the
counter electro-motive force generated in the primary by the
alternating core flux falls. Instandy, however, the primary
current increases, because the difference between the im-
pressed and counter e.m.f.'s of the primary is larger than it
was with the transformer working on no load. In fact, the
increase of primary current due to the loading of the trans-
former is just great enough to balance the de-magnetizing
action of the current flowing in the secondary coil. The re-
stdt is thai the flux in the care is maintained practically constant
by the primary, regardless of the load on the secondary.
The transformer is, therefore, automatic in its action;
the power taken by the primary from the supply mains
increases and decreases as the load on the secondary rises
and falls.

6* Voltagie and Current Relations. It has been stated
that the voltage induced in the secondary caii be calculated
once the total maximum flux (^ at the top of the sine wave, the
secondary turns N2, and the frequency in cycles per second
-are known. Just one-quarter of a cycle or 90 degrees after
the flux 0 has reached its maximum value, it has decreased
to zero. If the flux is alternating at the rate of/ cycles per
'second, then the time corresponding to one-quarter of a cycle is
r^ seconds, and the average rate ofchange, per second, of flux

from . 0 to zero during that time is ~T = ^f (2^ lines. If this aver-

4F
age rate of change of flux occurs through N2 secondary turns,

then the total average induced secondary voltage is

4f^N2
innnnnnnft ^^^*®» 8"*ce 1 00,000,000 flux lines must cut a con-
ductor in one second to induce a volt in that conductor. For
a sine wave, the effective value of the voltage, as indicated

178 ALTERNATING CURRENT SIGNALING.

by the ordinary voltmeter, is 1.1 times the average value, so
that the effective secondary voltage is:

^ ~ 100.000,000 *^-^ ^'^

j_ AAA f 0 Nz
"" 100,000,000
which is the fundamental equation used in transformer design.

Of course, the primary induced voltage can be similarly cal-
culated from the flux and primary turns. From equation (1 )
above, it is evident that the voltage induced in the primary
and secondary coils is simply proportional to their respective
turns, since the same amount of flux cuts each coil. Because
of the automatic action of the transformer already describ-
ed, the core flux remains constant in quantity regard-
less of the load and hence the primary induced voltage is
always sensibly equal to the voltage impressed by the primary
from the mains. Hence:

El Ni

— = — (2)

Where Ei is the voltage at which power is supplied to the pri-
mary, E2 is the voltage at which the secondary delivers power,
and Ni and N2 are the number of turns in the primary and
secondary coils respectively.

. The magnetizing force exerted on the iron cx>re by a load
current of Ii amperes flowing in the primary coil of Ni turns
may be expressed as the product IiNi, this product of amperes
times turns being known as ampere tarns; a given magnetizing
force can be produced either by a large number of amperes
flowing through a small number of turns, or vice versa. The
magnetizing action of the secondary current may be ex-
pressed by the prodnct 1 2 N^. where 1 2 and N2 are the sec-
ondary current and turns, respectively. It has been showA
that the magnetiadng action of the load currents in primary
and secondary balance each other; in other words, they. are.
equal. Hence,

h Ni = It N, (3)

and

I2 Nx

TRANSFORMERS. 179

Where Ii is the loed curjent in the primary; that is, the in"*
crease in current due to the load over and above the no-load
magnetizing current. In a well-designed transformer, this
no-load current for magnetization is insignificant as compared
with the normal load current, so that, for all practical purposes
it may be said that the the primary and iecondary currenta are inr
veraely proportional to their respectipe turns, aa shown b^ equation {4).

To illustrate the above relations, suppose a transformer
has 3300 turns in its primary coil, 273 turns in its secondary,
and power is supplied to the primary at 2200 volts. By
equation (2) above, the secondary voltage must be 1 10 volts,
since the primary and secondary voltages are to each other in
direct proportion to their respective turns. If the secondary
coil is to deliver 5 at^iperes. then from equation (4) the pri-
mary must be supplif^d with 0.23 amperes in addition to a
slight no-load current, for the primary cmd secondary cur-
rents are in invarae proportion to the number of their re-
spective turns*

7. Effect of Power Factor. If the secondary of a trans-
former is to supply, say, 1 100 watts at 1 10 volts at imity
power factor, the secondary current will, of course, be 10
amperes, since

Watts = I £ cos e (3)

Where cos 0 , the power factor, is imity. If, however, as is
very often the case in signal work, the secondary is required
to furnish the same amount of power as before, at say 0.3
power factor, instead of unity factor, then from equation (3)
the secondary current will be 20 amperes, and the transformer
windings must be large enough to supply this heavier current
without overheating. For this reason the caF>acity of
transformers should always be stated in K. V. A. (the usual
abbreviation for Kilo-Volt-Amperes, where one K. V. A. is
equal to 1 000 volt-amperes) and not in K. W. (abbreviation
for Kilo-Watts, one of which is equal to 1 000 watts).

When a transformer is supplying power at approximately
unity power factor, the secondary current is, of course, ap-
proximately in phase with the secondary voltage; the cor-
responding load current in the primary is opposite to the sec-
ondary current and of such a volume that the product I iNj ;
of primary )9P^4 P\i>^i^t^ ^y priPM^iy turns, just balances the

180

ALTERNATING CURRENT SIGNALING.

the secondary ampere turns to maintain the automatic trans-

fer of power between primary and secondary above explained.

These relations are illustrated in diagram (a) at the left of

Fig. 109, where OI 2 is
•El

♦El
®1 ApRIMARY LAG

tE2

JLAG ANGLE

ISECONDARY LOAD
»©i (a)

the secondary current,
OA is the correspond-
ing balancing primary
load current, OIq i^ ijie
no-load primary cur-
rent, and Oil the total
primary current conv
posed of load and mag-
netizing components
OA cuid OIq as shown.

Fig.' 109. Etfect of Secondary Power Factor OEi being the im-
on Primary Current Vector. pressed primary VoJ^

tage as usual. It wfll
be noted from diagram (a) Fig. 109 that with the secondary
operating at nearly unit power factor on a non-inductive load,
the total primary current Olj is much nearer in phase wit^
the primary impressed voltage than the no-load current OIq.
When, on the other hand, the secondaiy is feeding power to a
highly inductive load at a low power factor, the secondary
current Ol 2 in diagram (b) at the right of Fig. 1 09 lags away
behind the secondary voltage E2 and consequently the total
primary current Oli lags farther behind the primary impressed
voltage than does the no-load current OIj.

8. Effects of Coil Resistances and Magnetic Leakage*

The terminal pressure on the primary of a transformer has not
only to balance the counter electro-motive force induced in
the primary by the magnetic flux, but also has to be in excess
of it to overcome the ohmic resistance of the primary winding
and the inductive reactance caused by magnetic leakage.
Magnetic leakage in transformers is produced by a certain
number of magnetic lines not being interlinked with both pri-
mary and secondary winding. This amount of leakage is
very small in good modem transformers, because the primary
and secondary windings are interlaced in several layers. This
leakage cannot, however, be completely eliminated and must
be taken into account. The leakage lines of force induce a
counter e>m.f. in the primary which is npt tran^ipi^ted to the

TRANSFORMERS.

181

secondary and. therefore, causes a loss of voltage, much like
the loss of voltage due to the dead resistance <^ the primary
winding. The same two factors also diminish the secondary ter-
minal voltage. An actual transformer with resistance and
leakage losses acts just like an ideal transformer free from such
losses, but having connected in series with it a dead resist-
ance equal to that of the actual transformer and a reactahce
€X>il possessing an inductive reactance equal to that due to the
magnetic leakage in the actual transformer: Fijs. 1 10 shows an
deal transformer so connected.

-mm^r--mm^

mim^r-^ism^

Fig. 1 1 0. Practical Equivalent of an Ideal Transformer.

The corresponding complete vector diagram for the actual
transformer is shown in Fig. Ill, where oei, and oe2 are the in-
duced primary and secondary voltages respectively, while OIi
and OI2 are the total primary and secondary currents; the
same lettering applies to both Figs. 1 1 0 and 111. The voltage
E4 applied across points J and K in Fig.
1 1 0, has to be larger than ei by an
amount necessary to overcome the
ohmic drop in ri, and the inductive
drop in x^. In Fig. Ill this ohmic
drop is represented by the vector ei Ci
naturally in phase with and parrallel
with the primary current OIi, which
produces the drop. The inductive
drop across xi is represent<ied by Ci Ei
at right angles to the primary current
Oil. A total voltage of O Ei must
therefore be applied to the primary ter-
minals. Similarly, the secondary term-
inal voltage is less than the full secondary induced
voltage e2» by the amount lost in the secondary resi»^

Fig. 111. Complete
Transformer Vec-

111.
insfoi
tor Diagram.

182 ALTERNATING CURRENT SIGNALING.

■ — - — — — —

tance r2» and the reactance X2; the ohmic drop lost in
the secondary is represented in Fig. Ill by vector e2 C2
and the inductive drop by vector Q^^* respectively*
parallel and perpendicular to the secondary current Ol2*
These losses must be subtracted from the original induced
voltage e2 so that the net secondary terminal voltage is O E^.
Fig. Ill, therefore, covers the general case met with in com-
mercial practice of a transformer with iron losses, copper
losses, and magnetic leakage.

9. Efficiency. The efficiency of a transformer may be ex-
pressed as:

. Output of secondary in watts

Emciency = — i -, — -. 1 — (o)

Input of primary m watts

which is simply the ratio of secondary watts to primary watts
as indicated by watt meters in the two circuits. However,
it is generally more convenient for purposes of analysis to re-
gard the efficiency as:

. Secondary output

Secondary output + total losses
The losses in a transformer consist of (a) core losses in the iron
cmd (b) coi^>er losses.

(a) Iron Losses. The losses which take place in the iron
core of a transformer are divisible into hysteresis losses and
eddy current losses. Hysteresis losses may be roughly ascribed
as due to friction between the molecules of iron as the flux al-
ternates, and depend upon the frequency of the magnetizing
current, the value of the magnetic flux, and upon the volume
of the iron and its quality. According to a formiila devised
after much experiment by Dr. Steinmetz, the hysteriesis loss in
watts in a given volume V cubic centimeters of iron, work-
ing at a flux density of B lines per square centimeter is:

B'^fVn
^ ■" 10.000.000 ^^^

where / is the frequency and n is a factor depending on the
quality of iron; in modem silicon steel n is about 0.00093. It
is apparent from this formula that with a given quality of
iron the hysteresis loss will increase with the freql^ency and
the flux density.

Voltages are induced in the iron core itself by the alternating

TRANSFORMERS. 183

flux, juat as in the coils on the core. as. of course, the Rux in
reversing cuts the whole tnsBtietic circuit. These voltages
cause eddy carrtnlt to flow in the iron core in a plane at right
angles to the flui lines, and if the core were not built up of
thin sheets, painted on both udes to insulate one sheet from
another and piled in a direction such that eddy currents
would have to flow through the insulation between sheets,
then the watts lost through eddy currents would be excessive;
if solid iron cores were used in A. C. apparatus, even a smaU
voltage would cause enormous eddy currents to flow. The
eddy current loss in watts is in a volume of V cubic centi-
meters of iron at a frequency of /cycles per seconds is:

... V f^ B^ t* b W

" 10.000.000

where B ia the flux density, I is the thicknesa of each lamina-
tion in centimeters, and 6 ia a factor depoiding on the resiit-
0 57
ance of the iron; where silicon steel is used, b is about .M

Evidently, therefore, the thinner the laminations, the less
the eddy cur-
rent losses.

A graphical
illustration of
thesigntiicaRce
of the above
important for-

(orded by Pig.
112, which
shows the total

pound of a
weU known
grade of sili'
con steel rolled
in laminations,
0.014-inch
thick, a r
worked
varying fl

184 ALTERNATING CURRENT SIGNALINa

densities at frequencies of 25 and 60 cycles. From the
two lower curves, it will be seen that at a flux den-
sity of 1 0,000 lines per square centimeter the iron loss at 60
cycles is about two and one-half times the loss at 25 cycles.
It will also be seen from the next to the top curve that the loss
in laminations 0.025-inch thick at 60 cycles and 1 0.000 lines
is about 20 per cent, greater than the loss at the same density
and frequency in laminations 0.014-inch thick. Silicon steel
is a development of the last few years; it is not only remarkable
for its low -initial losses, but also because of the fact that its
losses do not increase after a transformer has been in service
for a long time. The top curve in Fig. 1 1 2 is the character-
istic of a common cheap grade of sheet iron whose losses in-
crease with ageing; from an examination of this curve, it is
evident that even the initial losses of the sheet iron are not to
be compared with those of the better silicon steel.

(b) Copper Losses. These losses are simply due to the
heating etf ect P R of the currents flowing in the primary and
secondary coils. Therefore, if a current of I x amperes is flow-
ing in a primary of R^ ohms resistance, and 1 2 amperes are
flowing through a secondary resistance of R2 ohms, the total
copper loss is:

W„=IiaRi+Ij2Rj (10)

Because of the fact that only a small current flows when the
transformer is running on no-load, the copper loss at that
time is almost insignificant, the principal loss being the iron
loss, which is constant at all loads, since the magnetic flux is
constant. Therefore, where transformers are always connect-
ed to the primary feeding mains (as is generally the case) re-
gardless of whether the transformer is loaded or not. it is
important that thin laminations of good steel be used in the
core to keep the core loss down, as it is going on all the time,
even when power is not being drawn from the secondary. On
the other hand, copper must not be sacrificed in the con-
struction of the transformer, lest the copper losses at full load
be excessive.

The copper losses in a transformer can easOy be calculated
from equation (10). So also may the core loss be calculated
from equations (8) and (9); these equations are fundamental
in transformer design, but after the transformer is built it is
easier to actually measure the core loss by open circuitiqg the

TRANSFORMERS. f85

transformer secondary and measuring the watts input in the
primary at normal voltage and frequency; knowing the pri-
mary current and resistance, the primary copper loss can be
detennined cuid, when subtracted from the total input as in-
dicated by the watt meter, th*. quantity left is the core loss.
Of course, there is no secondary copper loss since the sec-
ondary is open circuited.

10. Regulation. The open circuit voltage of the sec-
ondary of a transformer is necessarily greater than the full
load voltage because of the fact that when the transformer is
loaded, the load current causes a drop in both the primary
and secondary coils due to their resistance: in addition to the
resistance drop there is the reactance drop diie to magnetic
leakage. These two factors cause the available primary and
secondary voltages to be less than they otherwise would be
as prevoiusly explained in connection with Fig. 111. There-
fore, the secondary voltage rises as the load decreases. The
regulation of a transformer is the rise of secondary terminal
voltage from full non-inductive load to no-load, expressed in
per cent, of the full load secondary terminal voltage, the im-
pressed primary voltage being constant. For example, if the
secondary terminal voltage of a transformer is found to be
1 10 volts on full non-inductive load, and it is found that this
voltage rises to 11 2.5 volts at no-load, then the regulation by
foregoing definition is:

„ , . 112.5 " 110 ^^^ ■ ,,^

Regulation = rr^ • = 2.27 per cent. (1 1 )

Of course, in actual practice, the simplest way to determine
the regulation of a transformer is to measure the change in
voltage from full load to no load with a voltmeter, using the
above formula. In many cases it is necessary, however, to
calculate the regulation from predetermined values of the re-
sistance and reactance drops, particularly because these quan-
tities vary with the load and power factor, as will be evident
from an inspection of Fig. 111. No very practical formula
has been devised for the absolutely accurate calculation of the
regulation of a transformer. The following simple and quite
accurate method, however, is recommended by the Govern-
ment Bureau of Standards and by the Railway Signal Asso-
ciation. According to this method,' the regulation is com-
puted from the measured primary and secondary resistance

186 ALTERNATING CURRENT SIGNALING.

and reactance voltages with the aid of the following equations:

At unity power factor (non-inductive load)

„ , /1001R\

Regulation=^^— g— j% (12)

At 60 per cent, power factor

ReguUtian=[l00(^-^'^+°-«^]% (.3)

where E is the rated primary voltage. P the reactance voltage
drop an I the full load primary current exclusive of the ex-
citing current. The equivalent resistance R of the primary
and secondary combined is found by multiplying the second-
ary resistance by the square of the ratio of primary to second-
ary turns and adding the primary resistance.

The impedance voltage e is found by short-cincuiting th«
secondary cmd measuring the voltage n&quired <>tb s^d full
load current through the primary. The impe4ithqp voltage
is then: '

e= VP^ + I^R^ (14)

and consequendy the reactance voltage drop P at full load is:

P=Ve2'PR2 (15)

It is hardly necessary to explain that the percentage regu-
lation ought to be small; otherwise, as soon as the load comes
on the transformer the secondary voltage will fall rapidly.

From an inspection of Fig. 1 1 1 and equations (1 2) and (1 3),
it is obvious that the way to improve the regulation of a trans-
former is to use plenty of copper in the coils to minimize IR
drops, cmd to so interlace the primary and secondary wind-
ings, one with the other, that the magnetic leakage, (the seat
6{ reactance voltage drop), will be small.

11. Performance; Rating. Table I, shows what may
be expected of modem high grade commercial transformers in
the way of losses, efficiencies and regulations, at various loads
and power factors. In the case of transformers of the smaller
capacities listed, it will be noted that the regulation is actually
better at 60 per cent, power factor than 80 percent; this results
from the fact that as the power factor decreases, the resistance
drop becomes of less and less importance, as will be evident
after a study of Fig. 111. The characteristics of a large 1 00
K. V. A., 25 cycle, transformer are shown in Fig. 1 13.

Transformers are rated according to the power they can

TRANSFORMERS.

<leliver continuoualy
heating. In order to
icon Inatiti

i-inductive load, without over-

uniforniity in rating, the Amet-

o( EJectrical Engineers recommends that, where

TABLE

PERFOKMANOB OF OOMMEBOIAL TRANSFORMERS.

.....

Watts Loss

Parcant EtDclaacr

Copper

ffl

i^^ia

liia

1°?.

94 7

93 2

2 62

3 28

125

148

131

147

319

374

37 Si

240

B60

1 15

2.68

.„|

intended (or continuous service, the tem-
perature rise at full load shall not exceed a room temperature
<A 25 degrees
C. by more
than 50 d»-
greesC. Trans- ||
fonnera for sig- ^^
nal work are ^g
rarely, if ever, jg
subjected to 9
continuous full '
load, and, con-
sequently, the %FOWMF»CT0F

luiiwy sig- -«•";£. v:'rss£rr.':"""

nal Association

recommends that the final temperature, maintained for one
hour under constant full load at normal voltage and fre-
quency, shall not exceed a room temperature of 25 degrees C
by more than 50 degrees C, the ultimate rise of temperature
having previously been hastened if necessary by overloading
and over-excitatioa before the teat run of one hour. _'

TRANSFORMERS.

TRANSFORMER CONSTRUCTION.

12. Typea of Tranaformer. The essential elements of
A transformer are the iron core, the coils and their insulatjons.
tjie temunal board anij leadout wires, and the case with its
insulations. Depending on the relative arrangement of
ironcoreand coils, transformers may be clBSHified as (d) Core
type, (b)Shell type, or (c) Distributed Core type. In all cases,
of course, the iron core is built up of laminations painted on
both sidea to minimize eddy current losses.

CORE TYPE SHELL TYPE CORE TYPE

Flf. IM. Typn o( Tiuuformer Coic Conitructiitn.

(a) Core Type TrnnsfonnerB. This construction is il-
lustrated at the left of Fig. 1 1 4, where it will be seen that both
of the vertical legs of the iron core are stirrotinded by a wind'
ing; to cut down magnetic leakage half of the primary and
}iiii of the secondary are wound, one over the other, on each
leg BO that the coils may be said to be interlaced.

(b) Shall Type- This construction is shown in the mid-
dle of Fig. 114; here both primary and secondary are wound
interlaced, one with the other, over the center leg of the iron
core which almoet entirdy surrounds the coils. Fig. I IS ia

IM ALTERNATING CURRENT SIGNALING.

an bcIubI photograph of tuch « traniformer. the core and
windings complete with their terminal booed and leads bong
dearly shown
at the left.

illustrated » t
the right of
Fig. 114. is B

, of (a) and 0>)

above. Tha

Fig. US. Shdl Typ« Tnuufonucr. jf^^ jj^,^ ,;,^,

tists of four

magnetie circuits of equal reluctance, in multiple; each

circuit conuBtB of n separate cote. One leg of each magnetic

dicuit is built up of two different widdis ^ punchings,

forming such a cross-section that, when tJie four circuits

are assemUed together,

they interlock to form

a central leg, upon which

the ■ winding is placed.

The four remaining out-

«de legs occupy a pon-

tion surrounding the ccnl

at equal distances from

the centre on the four

sides. The complete

core with its cents and

terminals is shown in

Fig. 116.

As to the rdative

advantages of core and

R«. 115. DUtributedCoreTyi* shell types, it may U

said that the core type

has a lighter core of smaller sectional area than the shell

type. BO that more copper with a larger number of turns

is required with the core type, although the turns are of

a lesser mean loigth. Then, again, c^indrical form wound

TRANSFORMERS. 191

coils can be rafnclly wound for the core type, and these
coils have a large surface exposed for cooling. Altogether*
the core type, with its large available winding space, is
better adapted for high voltages which require many turns
with considerable space for insulation. The shell type, on the
contrary, is particularly suited to transformers of moderate
voltage, requiring few turns and litde insulation. The dis'
tributed core type combines the best features of both core and
shell constructions; i. e., a short mean length of turn in the
coils, and a short length of magnetic circuit; the magnetic cir-
cuit is of very low reluctance since the four circuits are all in
multiple.

13. Coils; Insulations. As previously stated, it is ad-
visable that the priiliary and secondary coils be well interlaced
with each other, if riiagnetic leakage is to be avoided. How**
ever, on account of ^e fact that a high voltage is generally
impressed on the primary coil, extreme care must be takoi not
only to insulate the pnbnary from the secondary, but also the
primary from the iron core, because, in case of a breakdown
in the primary msulation, the secondary coil or the case might
be at a dangerously high potential. For transformer working
on primary pressures of from 330 to 3,000 vcJts, and second-
ary pressures of from 33 to 220 volts, the generally accepted
rule is that the insulation between primary and secondary,
' and between primary and core, shall be capable of withstand-
ing a high voltage breakdown test of 1 0.000 volts A. C. for one
minute; for transformers whose primary voltage is over 3,000
volts, the testit^. Voltage is twice the rated primary normal
voltage. In such Cases, the insulation test between the sec-
ondary and core is 3,000 volts A. C. for one minute, although
this is often exceeded. As an additional safeguard a metal
plate, known as a ground shield, is sometimes placed direcdy
between the primary and secondary coils, so that, if the pri-
mary insulation breaks down the high potential will be carried
away from the secondary by the ground shield which is con-
nected to the iron transformer case, itself connected to a plate
or pipe buried in the ground at the transformer location.
After winding, the completed transformer core is thoroughly
heated cmd dried in a vacuum tank; after this drying the core
is flooded over with a hot insulating compound which

ALTERNATING ClHtRENT SIGNALING.

17. CompltlcC
ioal Botid Dial
«TypeT«™fu

Fii. 118. Oil Coded Uns

ia forced into every part of
the winding and insulation
at a very high pressure. This
tteatment. called imprtgnU'
lion, improves the insulation
of the transformer and pro-
tects it from moisture. The
transformer core shown at
the left of Fig. 115, was so
treatad, as will be evident
from itsshiny appearance.

14. Terminal Board
and Leads. In moat cases,
the ends of the secondary
winding are brought to a
terminal board carried by the
iron core body, as ahown at
the right of Fig. 115. At the
right of this view the core
body is shown assembled
complete in its case with the
cover of the latter removed;
the terminal board, made of
impregnated maple, carries
four terminals, the two out-
side terminals being the ends
of the secondary winding,
and the two inside terminals
are taps from the interior of
that winding. Heavy flexible
leads, not easily broken, lead
from the brass terminal posts
on the board through porce-
lain bushings, or ducts, to the
outside of the case. The pri-
mary voltage of moat trans-
formers of fair size is danger-
ously high, so that primary
leads are not brought to the
terminal board, where some

TRANSFORMERS.

one might receive accidentally a severe shock; consequently,
in Fig. MS, the primary leads are carefully taped and
insulated and lead directly out of the case through
poicelain bushings, these loads being made of heavy flexible
wire. A distributed core type transformer with a circular
porcelain terminal board, is shown in Fig. ) 1 7.

15. Case, Air and Oil Cooling. Small transformers of
one-half K. V. A. capacity or less, which are housed in relay
boxes or other shelters, are generallynot provided with a case;
•mall track transformers, such as the one shown in Fig. 1 19.
ace generally of this type, and are. consequently, said to be
air cotJtd.

Most transformers of over one-half K. V. A. capacity are
hung on a pole in the open, where a case must be provided, as
shown in Figs- 1 1 5 and 1 1 8, to protect the core and winding
from the weather; in addi-
tioa to this protection,
ttie case is generally filled
with a line grade of mineral
oil fiee from acid, alkali
and moisture. Oil carries
the heat generated in the
windings and core out to
the case much better than
would air, so that such
an oil-ceoltd transformer
will show a much lower
tempierature rise than a
similar air-cooled trans-
former. In addition to
this, the oil serves to
keep moisture out of the
windings and keeps them
■ oft and pliable. Of

course, oil is also an ex- p,,. 119. Air Coolid Tract

cellent insulator and acts Truuformer.

a break in the insulation after the latter has been damaged
by lightning. However, by means of a special impregnating
process, transformers of the line type shown in Fig. I IS may be

ALTERNATING CURRENT SIGNALING.

so protected against moisture as not tc

rem) in the c

16. Adjustable Filler Track Transformers, As has
been previously pointed out. the reBulation o( a transformer
deprnds, not only on the resistance of its coils, but also on its
magnetic leakage. In connection with Fig. 1 1 0. it was shown
that a practical transFomier might be considered as an ideal
tnuisformer with extemal resistances and reactances con-
nected in series with both primary and secondary coils; as the
secondary current increases, the resistance and reactance
drops begin to cut down the secondary terminal voltage more
and more. This fact is taken advantage of in the desiKB of
the so-called adJusiabU filler track transformers which are
intentionally designed with a large and easily variable mag-
netic leakage, so that they can be used for feeding a track cir-
cuit direct, eliminating the ububI external impedance be-
tween the transformer secondary and the track.

The construction of the adjustable filler transformer is illus-
«*««v/M*'N FLUX t"t^ "" Fig. 120. where it

"""*"'i^E*KAttE FLUX will be seen that the trans-

rpRIMARr foi'iner is of the shell type.
ICOIL The primary and secondary

tx/At are wound as usual on
the middle leg of the lami-
nated core, but they are
separated from each other
considerably to allow room
for two laminated wedge-
shaped iron filler blocks FF.
These filler blocks in the fin-
ished transformer are sup-
ported from the terminal
board on the top of the core,
and can be raised and low-
ered within the core by a
screw adjustn>ent ( accom-
plished from the terminal

^^SecONWBr

is. of c

^ per-

fectly evident that practical-
ly all the flux can be shunted
out of the secondary coil, if the filler blocks arc dropped hr

TRANSFORMERS. 195

dovm into the body of the core: with this adjustment, the mag-
netic leakage would be ao great that the secondary coil would
be practically dead, whereas, with the fillers all the way out
full voltage would be secured at the secondary terminals. By
intemiediate adjustments of the fillers, the magnetic leakage
can be regulated as desired, so that when the secondary
coil is connected to a track circuit, the proper voltage can be
secured at the relay. However, the moment a train enters
the track circuit, the re-
active drop due to magnetic
leakage rapidly increases and
the voltage at the secondary
H terminals falls. This action
I is iUustrated by Fig. 121.
> which shows how rapidly the
5 secondary terminal voltage
Q falls as the current increases,
a the filler being about one-
quarter of on inch Out of
the core in one curve and
nearly all the way in for the
Other or (lower) curve, which
Fi(. IZI. Chirutuiitio of ths latter, it is to be noted, is
Adiiuuble Filler Tmoifcwnicr. very steep. Were it not for
the reactance drop secured
through the use of the fillers, the secondary short-circuit cur-
rent would be many times more than indicated by the curves.
The transformer shown in Fig. 120 is generally provided with
a case and is oil -cooled.

Adjustable filler track transformer are generally used only
on center fed track circuits on electric roads, being then pro-
vided with a high voltage primary, connected directly to the
tnuumisiion line and one track secondary: this arrangement
is generally cheaper than one using a 2200'' 1 10' line trans-
former and an auxiliary air-cooled track transformer with its
limiting reactance or impedance. Where a simple adjustable
filler track transformer is used to supply a centre fed track
circuit. Oidy a commercial 2200''-ll0' line transformer is re-
quired at the end of the block for feeding the signal motor,
slot, lights, and local coils of the track relays.

1% ALTERNATING CURRENT SIGNALING.

17. Reactive Track Transformers. A smaller air-cooled
reactive transformer, working on the sample principle, is shown
in Fig. 128. This transformer is of the core type, the pri-
mary coil being wound on the upper leg and the secondary
coil on the lower leg. Here the fillers shown in Fig. 120 are
replaced by a U-shaped magnetic shunt which sets with the
U upside down on top of the upper leg of the transformer; the
U-shaped piece may be adjusted vertically so as to vary the
air gap between it and the upper leg of the transformer. It
will thus be seen that thus U-shaped block shunts flux out of
the secondary coil, just as do the fillers in Fig. 120. The
electrical action of the two transformers is identical.

18. Transformer Specifications. The general require-
ments for commercial line transformers in the way of per-
formance and material are excellently covered in the standard
specifications compiled by the U. S. Government Bureau of
Standards; copies of these specifications may be obtained
gratis from the Supt. of Documents, Washington, D. C.
The reader should, of course, also consult the standard
specifications included in the Railway Signal Association
Manual.

AIR COOLED TRACK TRANSFORMER.

(Single Secondary)

Capacity f 200 V. A.— 60cycW
1 100 V. A.— 25 cycle*

FRONT VIEW UK VCW

Fig. 122.
Characteriitica. The above tranafonner is used for feed-
ing steam road track circuits, and is generally provided with a
lO-volt tap on its primary for feeding signal lamps and relay
locals; the primary cannot be wound for more than 220 volts.
1 1 is provided with but one secondary having four terminals,
by means of which six voltages can be obtained. The maxi-
mum continuous output of the transformer is given above;
within these limits, the secondary can be wound for ony track
voltage, some of the standard windings being given below:
WINDINGS,

Cycles

Primary

Secondary

Volts

Amperes

110

e, S, 10, 12

.1'

ALTERNATING CURRENT SIGNALING.

AIR COOLED TRACK TRANSFORMER.
(Double Secondary)

/ 200 V. A.— 60 cycles
Copacty \ 100 V. A.~-25 eycle«

Bg. 123.

WOE VIEW

Characteristics. The above tranaformer is used (or feed-
ing two steam road track circuits. beinK provided with two
secondaries having four terminals each, giving six different
voltages on each coil The majcimum continuous total output
bf the tranaformer is given above; within this limit, the sec-
ondaries can be wound (or any track voltage, some of the stand'
ard windings bung given below. The primary coil, which
cannot be wound for more than 220 volts, is generally pro-
vided with a lO-volt tap (or feeding signal lamps and relay

WINDINGS.

Cycles

vSm'

Each Seeondan-

Volts

Amperes

110

L%«*'f6'f3,=.,5

TRANSFORMERS.

AIR COOLED TRACK TRANSFORMERS.
(Single or Double Secondary)
. f 220 V. A.— 60 cycle..
C-Px^tyt 100 V.A.~25 cycle.

Fi(. 124.

Charncteristics. The above traiwfonner is uted tor (eed-
■team road track circuits, and is generally provided with a 10-
volt tap cm its primary (or feeding signals lamps, relay locals,
etc.; the primary cannot be wound for more than 220 volts.

A. ^lown in Fig. 124, it has but one secondary, having four
terminals, by means of which six voltagea can be obtaioedi
however, it may also be provided with two secondariea, with
(our terminals each, so that two track circuits may be (ed
teparately. The maximum continuous total output o' the
traitsformer is given above; within this limit, the secondary
can be wound (or any track voltage, scKne of the standard
ungle secondary windings being given below; with two sec-
(mdaiies, the ampere capacities pier secoridary would be hal(
those giv«i below.

WINDINGS.

Cycles

'^Sff

Secondary

Tolta

Ampere*

220
5

a:5!7;io: 12I js

ALTERNATING CURRENT SIGNALING.

AIR COOLED TRACK TRANSFORMER.

{Sngle Secondary)
f 550 V. A.— 60 cycles
Cp«c.ty [ 250 V. A.-25 cycles

Fig. 125.

Charaeteristica. Thi> transformer may be used for feed-
ing either steam or double rail electtic road track circuits.
It is provided with one secondary, having (our terminals,
from which sin different voltages may be obtained.

The primary can be provided with a 10-volt tap
for feeding lamps and relay locals, but cannot be wound
for an impressed voltage of over 220. Some of the standard
windings are given below.

This transformer may also be made with an open magnetic
circuit for use on single rail tracks circuits on D. C. electric
roads, in which case its capacity is about 300 V. A. on 60
cycles, and 1 50 V. A. on 25 cycles.

WINDINGS.

■•5X'

Secondary

VolU

i„B».

110

BM}isM&.u.„

_^ ffiAN3ftJRi.<eftg.

AIR COOLED TRACK TRANSFORMER.

(Double Secondary)
I 550 V. A.— 60 cycle.
CpBcity [ 250 V. A.-25 cycle.

Fi,. 126.
Characterittic*. This tmlufornier is provided with two
Mcondarie. for feeding two ateHtn or double rail electric road
track circuits, where the total output required is not over the
limits above given; each secondary is provided with four ter-
minals, so that six different voltages can be obtained on each
coil, and the primary, which cannot be wound for more than
220 volts, is generally provided with a 10- or I2'valt tap for
feeding ugnal lamp, and relay locals. With the capacity
limits given, the secondaries can be wound for any track volt-
i standard winding is given below.
WINDINGS.

Cycles

vStr

Each Secondary

Volts

*"■""■

•ao

...

3. e, B. 12, 16. 18

■This particular transrormer Is provided with two primary taps
for 130 and 10 volta. respectively: the 10 volt part of the primary
winding has a capacity ot 0.5 amperes.

ALTERNATING CURRENT SIGNALING,

AIR COOLED TRACK TRANSFORMERS.

(2 or 4 Secondariea)

- . / 0.6 K. V. A.-«0 cycle.
Capacity \q^ ^ y ^ _25 ^^^^

Kg. 127.
CharacteriBtics. The above transfomier may be uaed for
feeding either steam or A. C. electric road track circuits and is
generally provided with a lO-vtdt tapon the primary for feed'
ing ngnal lampa and relay locals; the primary cannot be
wound for more than 220 volts-
It may be provided with either four Becondaries. as shown
above, or with two secondaries each having four taps to give six
voltages. The maximum total output of the transformer is
given above; without these limits the secondaries may be
wound for any track voltage. Two common windings are
given below.

WINDINGS.

Cycle.

'"vSS'

No. ot

Each Secondary

Volts

Ampena

110-10

3, 5. 9, 12, 14, 17
3, 5. «, 12. 14. 17

TRANSFORMERS.

AIR COOLED TRACK TRANSFORMERS.

(Reactive Type.)

Fig. 128.

Characterittic*. This tranafonneria provided with but Mie
track secondary and is intended (or feeding a single tracL cir-
cuit on electric roads using A. C. propulsion. No limiting re'
aistance or reactance is required between this transformer and
the track, as it is self-r^ulating ; for a description of the prin-
ciple on which it works, see page 194. Primary voltages ot
over 220 are not recommended. The common aecondary
windings are given below, the secondary being provided with
four taps, giving six different vintages.

WINDING.

Cycles

Secondary ,

VoltB

Open Circuit Volts

Short
Circuit
Amperes

...

2.7, 6.3. 8. 10.7, 13.3. 18

ALTERNATING CURRENT SIGNAIJNG.

TRANSFORMERS.

205

LINE TRANSFORMERS.

(All Capacities and Voltages.)

1. Function. In 1 K. V. A. capacity, or thereabouts,
these transformers (Fig. 129) are used at signal locations for
stepping down the transmission voltage to a lower voltage,
generally 1 1 0 or 220 volts, to feed signal motors, slots, and
the primary side of track transformers. As step-up trans-
formers, they are used in larger sizes in the power house to
step up the alternator voltage to that of the transmission.
These transformers are not prooidcd with track secondaries.

2. Voltages. The high tension side may be wound
for 2200, 3300, 4400 or 6600 volts. The standard voltages for
the low tension side are 1 10 or 220 volts, although other volt-
ages can be provided where required. At a slight additional
cost, 5 and 1 0 per cent, taps can be furnished on the prima-
ry to compensate for variations in the primary voltage.

3. Capacities and Weights. These transformers can be
furnished in the standard sizes listed in the table below. The
data given for shipping weight and oil is for 2200-volt trans-
formers.

TABLE I.

Fig. No.

K. V A

25 Cycles

60 Cycles

Approximate

Quarts
Oil

Shipping

Quarts

Shipping

Weight

Oil

Weight

0.6

180

130

1.0

180

130

i.r>

200

145

2.0

235

160

2.5

275

195

3.0

350

210

4 0

375

245

5.0

455

295

7.6

615

395

755

455

955

116

660

1110

135

800

1280

170

925

116

1550

225

1045

135

2070

230

1410

170

2350

240

1635

225

2400

280

1930

220

206 ALTERNATING CURRENT SiGNALINa

4. Construction. These transformers are of the dis-
tributed core type, illustrated in Fig. 1 1 7, and are provided
with an oil-filled case; they are ordinarily furnished complete
with oil for filling the case, and also-^straps, or hangers, for
supporting the transformer on the pole

The distributed core construction, the use of plenty of cop-
per, and the employment of silicon steel having a low hysteresis
and eddy current loss, result in a remarkable high efficiency
and good regulation; furthermore the silicon steel is subject-
ed to a peculiar heat treatment before assembly in the core,
and this prevents a so-called ageing effect, which would result
in a serious increase in the core losses after the transformer
had been in service for a time, the losses increasing as the
transformer becomes older. Silicon steel prevents this.

Special care is taken in the insulation of the windings, as
upon this depends the safety with which the transformer may
be handled; for example, 2200 volt transformers of this type
are required to pass an insulation test of 10,000 volts for one
minute between the primary and the core, and between the
primary and the secondary; when required they can be fur-
nished insulated to withstand a 1 5,000 volt ground test. The
workmanship is of the highest order, and it is believed that these
transformers, the result of twenty years experience, are un-
equalled for safety, durability, efficiency and regulation.

TRANSFORMERS. 20:

COMBINED LINE AND TRACK TRANSFORMER.

UCnOtMLFRMTVU

!• Coits. "Thia transformer may be provided with one,
two or three necondariea, any of which may be wouad for either
track feed or signal operation.

2. Voltagaa. The primary may be wound (or any volt-
age up to 2300. The aecondaries may be wound for any ordi-
nary track or signal voltage, a list of standard voltages being
given in Table II, following, where it will be noted that in
some cases the transformer is not fully loaded.

3. Capacity. The maximum total continuous output of
aU coils is I K. V. A. on 60 cycles or 0.3 K. V. A. on 25 cycles.

4. Conatructicn. The transformer is of the oil im-
mersed shell type. A high grade specially heat treated non-
ageing steel is used in the core to insure continuous high ef-
ficiency and the primary is insulated to stand a 10,000 volt
breakKlown test to core nnd each secMkdary; when required.

20d

ALTERNATINC CURRENT SIGNALING.

the primary can be insulated to withstand a 1 5,000 volt ground
test.

5. Weights; Oil Required. Transformers with winding
numbers 2, 3, 21 and 22 below require dyi quarts of oil» and
the weight without oilis 1 05 lbs. ; all others require 8^ quarts of
oil, the weight without the latter being 1 1 5 lbs.

TABLE II.

Cycles

Pri-

LIGHTING

TRACK

Fig.

per

mary

Second

Volts

Am-

No.

Volts

Am-

peres

Coils

peres

2200

61-58-56

15-12.5-

-53

10-7 . 5-5
-2.5

110

225

15.7

110

23-19.5-
14.4-10.9

2200

122-116-
110-105

1.5

2200

115-110-
105

19.7-16-
14.5-10.5

220

120-115-
110

15-12-9
-6

500

58-55-
52-49

1.5

13-10
6.5-3.3

2200

115-110-
109-106

28-24 . 5-

16-12-

8.5-3.5

2200

60-57 . 5
55-52 . 5

18-15-
12.5-9
5.8-3.4

110

12-10.3-
8.2-6.2-
4.1-2

1100

120-117-
114-110

9.1

220

120-117
114-110

9.1

110

•

21.2-15.9
11.3-6

110

11.3-10.6
-10-9.4

100

110

15.2-14.5
13.7-13

2200

120-115-
110-105-
10

3.7-3. 1-
2.5-1.9-
1.2-0.6

5.6

2300

120-117-
113-110

7.2

12-9.4-

6.7-5.3-

2.7

2300

120-117-
113-110

7.2

12.6-11.9
11.2

TRANSFORMERS.

209

TABLE II

(Continued).

LIGHTING

TRACK

Cycles

Pri-

Fig.

per

mary

Am-

No.

Am-

Second

Volts

peres

Colls

Volts

peres

2300

18.1-14.1
-10.2-6.2

400

600

2 coils

455

65-52

2.6

9.6

2300

120-115-
110-105

3.6

12-6-4-
2

7.6-6.2-
5-3.&-2.5
1.3

tlO ALTERNnTtNG CUORENT SIGNAUNC.

COMBINED LINE AND TRACK TRANSFORMER.

. fl.5K. V.A.— 60cycUi
Capacity |o„ K y f^_2^ ^y^^

1. CoU*. This transformer may be provided with one,
two or three secondaries, any of which may be wound for track
tctd or signal operation. See Table II I on next page (or a few
of the standard windings; in some cases it wiU be noted that
the transformer is not fully loaded.

2. Voltasea. Same as those given for Fig. 130.

3. Capacity. The maximum total continuous output of
all coils is I.S K. V. A. on 60 cycles or 0.75 K. V. A. on 25 cycles

4. Construction. Same as that of transformer described
in connection with Fig. 130.

5. Wsighti Oil required. Weight without oil, 175 lb«u
oil required, 13 quarts.

IIIANSFORMERS.

211

TABLE III.

LIGHTING

TRACK

Cycles
per

Pri-
mary

Fig.

Am-

No.

Am-

Second

Volts

peres

Coils

Volts ,

peres

2200

60-57 . 5-
55

10.5

6. 1-4. 9-.
3.7

140

2300

146-134-
120-115-
110

4.5

15.3-12.6
10-7.3

2300

135-127-
120-115-
110

20-1 fr-
12-7 . 5

7.5-6.2-5
-3.8-2.U
-1.3

2200

135-125-
116-110

7.3-6-5.3
4.6-4-3.3
2.7-2-1.3
0.7

2200

120-115-
110-105

3.4

10.6-8.6-
7.2-5.2-
3.3-2

2200

135-130-
125-120-
115-110

6.6

8-6.7-5.3
4-2.6-1:

220

66-63-60

2300

120-115-
110

220

20-15

2200

148-134-
120-115-
110

2.5

28-21.8-
15.7-9

2400

160-135-
120-116-
110

20-16-1?

-8

60 "

2200

170-155-
140-118-
110

10.5

12-9.3-
6.6-4

110

12-10-8
6-4-2

2200

120-115-
110

2200

116-110

4.75

16.5-14.3

-13.2-11-

9.9-7.7

2080

115-110

18-14.5-
10.8-7-6
-2.5

110

15-14-13

180

ALTERNATING CURRENT SIGNALING.

COMBINED LINE AND TRACK TRANSFORMER.

/ 2 K. V. A.— 60 cycles
Capacity | , ^ j, y j^ _25 ^^|^

1. Coils. This transformer may be provided with from
one to three secondaries, any of which may be wound for track
feed or signal operation

2. Voltages. Maximum primary. 4400; the secondary
coils may be wound for any ordinary track or signal voltage,
the standard windings being given in Table IV on next page.

3. Capacity. The maximum total continuous output of
all uhU is 2 K. V. A. on 60 cycles and 1 .0 K. V. A. on 23 cycles.

4. Construction. Same as that described in connectioD
with Fig. 130.

5. Weight; Oil required. Weight without oil. 240 Iba.;
oil required. 20^ quarts.

TRANSFORMERS.

213

TABLE IV.

Pig.

Cycles

per
Second

Primary
Volts

LIGHTING

TRACK

Volts

Am-
peres

No.
Collfl

Volts

Am-
peres

60
25

2200
4400

115-110

120-115-
110

1
1

16-13-10
-7

22.6-1&-
13.5- &-
4.5

214

ALTERNATING CURRENT SIGNALING.

COMBINED LINE AND TRACK TRANSFORMERS.
ADJUSTABLE FILLER TYPE.

1. Function. The transformers shown in Figs. 130, 131
and 132 may be provided with adjustable magnetic leakage
fillers, (page 194), in which case no limiting resistance or
reactance is required between the transformer and the
track. They may be provided with two secondaries, one
of which may be wound for track feed and the other for
signal or lighting operation; or they may be provided
with one large track coil, but not with two.

2; Voltages. The primary may be wound for any volt-
age up to 2300. The secondaries may be wound for any ordi-
nary line or track voltage, a list of the standard voltages being
given below.

3. Capacity. The data given below in Tables V, VI
and VII indicate the capacity of these transformers with
various windings.

TABLE V.
(Transformer Fig. 130

LIGHTING.

TRACK.

Fig.

Cycles
per

Primary

fti— j_

Second

Volts

Amperes

Open Cir-
cuit Volts.

Short

Circuit

Amperes

1100

8-4

400

9.6

60-50-
40

3.6-1.76

ito

120-100
-80

3.6-1.76

220-200
-180

3.6-1.76

2200

10.6

110

10.3-7.3

200

8.6

120

2200

9-4.6

126

440

11.4-6.6-

,, ■

2.2

220

14.5-9-8.3
-2.8

440

14.5-9-8.3
-2.8

2200

18.8-14.4
-9.8-3.2

112

116-112-109

0.71

6.9

4.1-3.4-
2.9

TRANSFORMERS.

215

TABLE VI.
(Transformer Fig. 131)

Fig.

Cycles
per

Primary
Volts

LIGHTING.

TRACK.

Volts

Amperes

Open Cir-
cuit Volts.

Short
Circuit

Second

Amperes

550

59-57-55-53

2.5

10-8-6-4

100

11.8-8.8-
5.9-3

150

2000

11.4

2200

2.7

7.4

130

2200

6.7-5-3.4

330

120-115-110

4.9

3.35

140

330

120-115-110

4.9

6.8

2200

128-122-117-
116-113-110

1.45

20-16-10
-6

2000

20.6 .

2200

12-8-4

110

25-17.5-
8.7

125

2200

32.9-25.6
18.3-10.9

144

2200

29.6-18.7

-7.7

220

120-115-110

1.8

29-21.7-
14.5-7.2

2200

61-59-57-55

16-13-10

-6

lfr-13-10

2200

125-120-115-

7.6

110

-6

2200

136-126-120-
118-115-110

4.6

22-16-10
-5

TABLE VII.
(Transformer Fig. 132)

Fig.

Cycles

per
Second

Primary
Volts

LIGHTING.

TRACK.

Volts

Amperes

Open Cir-
cuit Volts

Short

Ch-cuit

Amperes

1
2

25
25

1100
2200

60-57.5-65
119-115-110

8.5

5.2-3.6-

2.1

18-16-12

135
140

t\i ALTERNATING CURRENT SICNALtNC

COMBINED LINE AND TRACK TRANSFORMER.
OPEN MAGNETIC CIRCUIT TYPE.

Fig. 133.

1. Function. The transformer shown above i« inbmded
for (ceding single rail track circuits on electric roada using D.
C. propulsion. The core has an open magnetic circuit (as
shown by the vertical white line between the halves of the
core in the right hand view), so that the direct current passing
through the track coil will not saturate the iron. The trans-
former can be equipped with two secondaries, one of which is
a track g<mI, and the other a line coil for feeding signals or
lights.

2. Voltages. The primary may be wound for any volt-
age up to 2200. while the secondary may be wound for any of
the usual voltages required for track feed or signal operation.
A few of the standard windings are given in Table VIII below.

3. Capacity. The maximum total continuous output i«
I K. V. A. on 60 cycles or 0.5 K. V. A. on 25 cycles.

4. Construction. Shell type, oil immersed. Specially
heat treated non-aging steel used in the core to insure a con-
tinuous high efficiency. Primary is insulated to stand a
lO.OOO vtAt test to each secondary and core.

TRANSFORMERS.

217

5. Weight ; Oil Required. The weight of the transformer
without oil is 1 33 pounds. Ten quarts of oil are required.

TABLE VIII.

lighting'

TRACK

fJk9

Cycles

Primary

—

_ —

Fig.

per

Volts

Second

Volts

Am-

No.

Volts

Am-

•

peres

Coils

peres

220

8 1 1 13.5

500

1.5

22.6

440

1.6

22.6

2200

13.5

440

110

0.8

8.6

22.5

110

18-14

500

1.6

22.5

220

120-115-
110

110

13.5-8-
6.5

220

48.6

1.6

8.6

22.5

1100

48.6

1.6

22.5

550

48.5

1.5

22.5

8.6

22.5

1100

6.76

1100

60-57.5-
66

1.6

9.6-6

110

22.6

560

60-67.5-
65

1.6

9.6

550

1 60-57.6-
56

9.6

2200

10.5-8.1

7.5

340

1.6

CHAPTER VII.

RESISTANCES AND IMPEDANCES FOR
TRACK CIRCUIT WORK.

ALTERNATING CURRENT SIGNALING

CHAPTER VII

RESISTANCES AND IMPEDANCES FOR TRACK

CIRCUIT WORK.

1. Function. The track secondary coil of a well de-
signed transformer is of comparatively low impedance, as it
consists of a few turns of heavy wire. In consequence of this,
an excessively heavy cur-
rent would flow through
such a coil with a train
on the track circuit, if

the coil would be prac-
tically short circuited
and burned out if a train
stood on the track cir-
cuit for any length of F^. 135. Tnck Circ
time and in addition a

lot of power would be wasted. Such current Lmiting devices,
consisting of either a simple reaiatajice tube or an impedance
coil, are called Iracli retiatancts or tradi impedances, as thecaM

In addition to their function in limiting the short circuit
current with a train on the track circuit, tisck reaistance* and
impedances have an important influence on the phase rela-
tion between track and local currents in two-element relays.
Track resistances, such as the
one shown in Fig. 1 33, consist
of H few turns of coarse wire
wound on an insulating tube
and are practically non-in-
ductive, so that when con-
nected between the tians-
former and the track they do

not alter the phase relation ■

of the current flowing into F>t- 1^ Tnck Cuwit

the track circuit with refer- liiip«dw>™.

222 ALTERNATING CURRENT SIGNALING.

enct to the voltage. Track impedances (Fig. 1 36) consist of
a coil of wire wound around a laminated iroii core and are con-
sequently highly inductive, so that when connected between
the transformer and the track the current is caused to lag
considerably with reference to the voltage. In the case of
two elemeht relays, such as the galvanometer or the induction
motor (polyphase), proper phase relations between track and
local currents must be obtained before the relays will operate
economically, and the correct selection of resistance or im-
pedance between the transformer and the track is therefore
an important matter.

2. Selection Between Resistance and Impedance for
Track Circuits Using Vane Relays. The production of torque
in the single element vane relay depends simply on the in-
tensity of the current flowing through the winding cuid in this
case, therefore, the question of phase relations does not arise.
In the interest of power economy it is, however, advisable to
use an impedance between the transformer and the track
wherever possible, most commercial impedances having a
power factor varying between 0.1 and 0.3, in which case the
voltage drop through the impedance is practically wattless.
On steam road track circuits, impedance Fig. 137 is generally
used, and on some double rail electric road track circuits.
Figs. 138, 139 or 140, depending on the current taken by the
impedance bonds.

Oti ail single rail track circuits where either D. C. or A. C.
propulsion is employed, the use of an impedance is rarely pos-
sible, and instead, a resistance, like those shown in Figs. 142
and 143, must be employed as the iron core of an impedance
would be saturated by the leakage propulsion current passing
through the impedance coil, as explained in Chapter V; with a
saturated iron core, the impedance would lose most of its self-
inductive, or choking, effect, and, thus, an excessive current
would be allowed to flow from the trsmsformer to the track.

3. Selection Between Resistance and Impedance for
Track Circuits Using Galvanometer Relays. The local coils
of this relay consist of a large number turns of fine wire and
are consequently highly inductive, having a power factor of
approximately 0.4; the armature, on the other hcuid, consists
of only a few turns of heavy wire and its self-inductance is

TRACK RESISTANCES AND IMPEDANCES. 223

negligible, the power factor being almost unity. The ad-
justment of the ii^iase relation of the currents flowing in the
two elements may be effected by inserting resistance between
the transformer and the track, and also another resistance in
series with the local, thereby bringing the armature and local
currents in phase at a higher power factor, resulting in a con-
siderable waste of heat energy in both resistances. Since
the production of armature torque is simply a question of cur«
rent, and not of power, the most economical adjustment will
be obtained when the power factor of the complete armature
and field circuits is as low as possible; therefore, power will
be saved if, instead of the above resistances, the low power
factor local is connected directly to the line and an impedance
is inserted between the transformer and the track, thus caus-
ing the armature current to lag in phase with the local cur-
rent. Due to the low power factor of the impedance, the
voltage drop across it is nearly wattless.

On most steam road track circuits impedance Fig. 137 is
therefore generally used, and on electric roads with double
rail track circuits and impedance bonds (where, since the
bonds act as a shunt, but little propulsion current flows
through the transformer circuit) impedances Figs. 137, 138.
1 39 or 1 40 may be used, these being always provided with an
air gap, not only to secure adjustment of the impedance value,
but also to keep the core from being saturated by such pro-
pulsion current as may flow. The magnitude of the ballast
leakage resistance in both steam and electric road track cir-
cuits, and the current taken by the impedance bonds in the
latter case, have a very important influence on the question
of phase relations, however, and the final decision as to
whether resistance or impedance should be used between the
transformer and the track can only be made after laying out
a vector diagram covering the actual conditions in point; this
matter is fully discussed in Chapter XI II.

4. Selection Between Resistance and Impedance for
Track Circuits Using Poljrphase Relays. Unlike the gal-
vanometer relay, the polyphase relay works most economically
with the track and local currents in quadrature, as explained
in Chapter IV; the local and track coils are of the same size,
th^ are both wound in an iron core and their power factors

224 ALTERNATING CURRENT SIGNALING.

• -

are, consequently, equal and low, about 0.65. It becomes
necessary, therefore, to secure phase displacement by artificial
means and for this purpose in steam road work, a small re-
sistance housed inside the relay is generally connected in
series with 'the loccd coils, so that the power factor of this
element becomes as nearly unity as possible. Impedance
Fig. 1 37, having a power factor of about 0.2, is then connected
between the transformer and the track, and this, working
in connection with the impedance of the rails themselves,
causes the current in the track element of the realy to lag ap-
proximately 90 degrees behind the local current.

On electric roads, however, due to the comparatively laxge
A. C. current taken by the bonds, and even on some steam
road track circuits with excessively large ballast leakage!, it
becomes most economical to connect a small reactancit^ in
' series with the local element of the relay (housed inside the
relay case), and a- resistance Fig. 142 or 143 between the trans-
former and the track; then the local current lags behind the
current in the track element, giving the pheise displacement
necessary for the production of a rotating field. It is not
necessary that the phase difference be a full 90 degrees, and
in fact this is rarely attained, but the nearer it is to 90 degrees
the better from the standpoint of power economy. Before
deciding to use either resistance or reactance, however, all the
factors, such as ballast, weight and bonding or rail, current
taken by impedance bond, etc., should be taken into consid-
eration and a vector diagram laid out as explained in Chap-
ter XIII.

TRACK RESISTANCES AKD IMPEDANCES. 225

TRACK IMPEDANCE FOR STEAM OR A. e
ELECTRIC ROADS.

1. Wh«re UMd. This impedance (Fig. 137) u demgned
primarily for lue on ateom roads. It i« not of aufficiaDt
capacity for D. C.

electric roads, but
where the current
taken by the imped-

too heavy it may be
uaedon double rail
track circuits on A.
C. electric roads.

2. Description.
1 1 conrists of a form
wound coil, iropreg-
nated (or pratectioD

assembled in a lam-
inated iron core, di-
vided into two sep-
arate parts, thelow'
er halt of the cons
being fixed to a jap-
anned wooden base
and the upper half
being adjustable.

3. Charact er-
istics. The coil is
provided with six
taps, and the im-
pedance in circuit
may thus be adjust-
ed over a constder-
able range as shown I
in the following
table, which covers |
a few standard
windings. A further
adjustment of the

226

ALTERNATING CURRENT SIGNALING.

imF>edance v/alue may be secured by vaiying the air gap be-
tween the top and bottom halves of the core, the air gap being
increased to decrease the impedance, and vice versa. The
maximum volts, amperes and impedance values tabulated be-
low are for the whole coil in series; when the lower taps are
used, the coil will stand greater currents than those given.

Fig.

Max.
Amperes
Constant

Load

Max.
Volts

Fre-
quency

Impedance

Air
Gap

Max.

Min.

1
2
3
4
6
6

7
8
9

6
6
6
6
8
7
10
7
3

18
42
10
22
10
22
7
11
35

25
60
25
60
25
60
25
60
25

3.0
7.1
1.6
3.6
1.3
3.1
0.7
1.6
11.7

0.5
1.3
0.3
0.6
0.3
0.8
0.2
0.4
2.2

0.012"
0.012"
0.035"
0.035"
0.012"
0.012"
0.035"
0.035"
0.012"

TRACK RESISTANCES AND IMPEDANCES.

TRACK IMPEDANCE FOR ELECTRIC ROADS.

1. Where Used.
This impedance (F^ig-
136) is primarily design-
ed for use on double rail
D. C. electric road track
circuits. It cannot be
used where two abutting
track circuits are fed
from the same trans'
former secondary. For
this latter service, the
impedance described in
Fig. 140 should be em-

coil of heavy copper im-
pregnated to protect it
against moisture, assem-
bled into a laminated
core divided into two
parts, the lower half of
the core being fixed to a
japanned wooden base
and the upper half being
adjustable.

3i Ctiaracteristice.
TTie maximum volts.
amperes and impedance
values are tabulated
below; the impedance
may be varied over a
wide range by adjusting
the sir gap, the latter
being increased to de- ,

the impedan

END VIEW
{.138. Truck lmp«dMi»l«D.C«
A. C. Bcctric Rouli. Typs A.

228

ALTERNATING CURRENT SIGNALING.

Fig.

Max.
Amperes
Constant

Load

Max.
Volts

Fre?
quency

Impedance

Max.

Min.

1
2
3

4
6
6

70
60
20
30
25
30

0
21
28
35
20
35

25
60
25
60
25
60

■

1.1
2.8
11.0
8.0
6.25
5.6

0.1

0.21

1.0

0.6

0.8

0.62

TRACK RESISTANCES AND IMPEDANCES. 229

TRACK IMPEDANCE FOR D. C. OR A. C. ELECTRIC
ROADS. {Type "B")

1. Where tued.
Thia impedance
(Fig. 139) i« pri-
Tnarily intended for
use on double rail
track circuits on
either steam or elec-
tric roads, its capa-
city being some-
what less than that
of the impedHnce
shown in Fig. 138;

where two abutting
track circuits are
fed from the same
track tranaformer
secondary. For this
latter service use
the impedance illus-
trated in Fig. 140.

2. Description.
It is an enlarged
form of die steam
road impedance
shown in Fig. 137.
being, however, pro-
vided with a porcel-

3. Character-
istics. The maxi-
mum volts, amperea
and impedance (at
full load) are tabul-
ated below: The

230

ALTERNATING CURRENT SIGNALING.

Max. Amperes
Constant Load.

Max. Volts

Frequency

Impedance

Max.

Min.

1.0

0.08

TRACK RESISTANCES AND IMPEDANCES. 231

TRACK IMPEDANCE FOR ELECTRIC ROADS

CTypoC.)
i. Whera ua«d. This impedance, like that shown in
Figs. 1 36 and 1 39. is intended for use on double rail electric
road track circuits, but is provided with two separate coils.
MM being <xmaect»d into each track circuit from the trans^
former, thia arrangement being used to prevent interference
between abutting track circuits when two such tracks are fed
at their meeting point from the same transformer secondary;
this impedance ia, therefore, intended only for such a double
track fed layout.

Fig. 140.

2. Construction. The general construction is the same

B* that described in connection with Fig. 138, with the above

exception; in the present case, however, the coils are provided

with taps and die air gap adjustment is made by means of

3. CharacteriaticE. The maximum volts, amperes and
impedance values are given in the table below; the impedance
may be varied over a wide range, first by means of the taps on
the coils, and secondly by adjustment of the air gap.

232

ALTERNATING CURRENT SIGNALING.

Fig.

Max.
Amperes
Constant

Load

Max.
Volts

Fre-
quency

Impedance

Max. Min

1
2
3
4

60
30
50
40

12
30
28
18

25
25
60
25

1.0 0.2
4.3 1.0
2.25 0.45
2.25 0.45

TRACK RESISTANCES AND IMPEDANCES. :

RELAY SHIELDING IMPEDANCE COIL FOR D.
ELECTRIC ROAD SINGLE RAIL TRACK
CIRCUITS.

1. Where Used. This impedance coil is to be connected
acrosa the track terminala of relays (usually of the vane type),
used on single rail D. C. electric road track circuits, in those
cases where the D. C. propulsion drop in the return rail may
be so great as would cause an excessive D. C. current to pass
through the relay, were the above impedance not connected
across the terminals to shunt out the direct current! in this
connection, see the discussion of single rail track circuits in
Chapter V.

2. Description. The coil condsts of a few turns of heavy
copper wound around a laminated iron care, the latter being
of the open magnetic circuit type to guard against saturation.
It is often supported and housed as shown in Fig. 3. Chapter I.

3. Characteristics. Its current carrying capacity and
impedance are given below.

234

ALTERNATING CURRENT SIGNALING.

Fig.

Max.
Amperes
Constant

Load

Fre-
quency

Imped-
ance

Air Gap

1
2

40
40

60
25

9.3
4.0

0.126"
0.125"

TRACK RESISTANCES AND [MPEDANCES.

236

ALTERNATING CURRENT SIGNALING.

TRACK RESISTANCES FOR STEAM OR ELECTRIC

ROADS.

1. Where Used. The resistance tubes shown in Fi^^s. 142
and 143 are for use on steam or electric road track circuits.
Which size should be selected depends on the current to be
carried and the resistance required, these quantities depend-
ing on the length of track circuit, baRa^ leakage, current
taken by impedance bonds, etc.; a track circuit calculation,
as described in Chapter XII 1, will show what the value of the
resistance between the transformer and the track should be
as well as its necessary current carrying capacity.

2. Description and Capacity. The units consist of one
or more wire wound asbestos tubes provided with porcelain
heads and supported on an iron frame; they are therefore fire-
proof. Six terminals can be furnished but four are generally
sufficient. Within the watt ratings (I^ R) given below, they
can be provided with any winding required.

SIZES AND RATINGS SU RESISTANCE TUBES

Size

Overall Dimensions

Continuous
Rating-
Watts

Length

Height

Depth

SU 201 A
SU 101 A
SU 102 A
SU 103 A

9ir
9ir

7"
9H"

IH"
2"

2"
2//

160

240

TRACK RESISTANCES AND IMPEDANCES.

TRACK RESISTANCE FOR D. C. ELECTRIC ROADS.

1. Function and Characterlitica. Tliis t
intended for use in ungle rail track circuit work on D. C. elec-
tric roads ubidk very
heavy propulsion
currents and long
blocks, in which case
the resistance may
be used between the
transfonner and the
track, the relay and
the track, or in both
places. It is de-
signed to be >us- R(. 144.
pended on the bolts

projecting beyond the grids, as ahovm in the above drawing;
see Fig. 3. Chapter 1, for an e][ample of its housing.

It consists of a number of grids cast out of a special grade of
iron, these grids being connected in series to make a total re-
sistance of one ohm; it may also be insulated into two sectiMU
of one-half ohm each. The normal current carrying capacity
either way ia 20 amperes, but the reMStance will stand mo-
mentary overloads of some 20 times normal curroit.

CHAPTER VIII

SIGNALS.
(Part I)

SEMAPHORE SIGNALS.

CHAPTER Vin
SIGNALS.

(PiiptI)
Semaphore Signal*.

Looking at the matter from a mechanical atandpcnnt, alter-
nating current signal ihecKanismB reaemble direct current
mechanisms in all important reBpects. It is in the electrical
portions— the motor and the holding device — that the char-
acteristic diilerences are found. As a matter of fact, most of
the better known types of signal mechanism now on the mar-
ket are constructed so as to be easily convertible from direct
current operation to alternating current operation through a
simple interchange of motors and slots. As all alternating
current signal mechanisms employ cither induction or com-
mutator motors as prime movers, and either tractive magnet
or induction slots as holding clear devices, these chatacter-
ittic dements deserve a thorough [treliminary study.
ALTERNATING CURRENT MOTORS.
Induction Motor.

I. Elenients. In its electrical behavior, the induction
motor is the exact electro-magnetic equivalent of an ordinary
transformer with a considerable amount of magnetic leakage

Fic- 145. EJwnenls of tl
between primary and aecondHTy coils. It consists of two elo-
mcnts; first, the attdor, which it a stationary outer ring or
shell of laminated iron, slotted on its inside face to receive the
primary windings, and, second, the roCor, which is A cylindri-
cal laminated iron core or drum, slotted on its outside face
to take the aecondaiy winding, and rotating within the atator

242 ALTERNATING CURRENT SIGNALING.

bore, the motor shaft beings keyed to the spider which carries
the assembled rotor laminations and their winding. At the
right of Fig. 1 43 will be seen a laminated stator core for a sig-
nal motor, slotted and ready to receive the primary winding;
the completed stator, with the end connections of its windings
insulated and taped, is shown at the left of the photograph.
The rotor with the secondary winding is illustrated in the
center of the photograph, with a rotor lamination immediately
to its left resting against the finished stator; in this case, as in
all induction motors for signal work, the secondary winding
consists simply of heavy copper or brass rods, driven through
the rotor slots and connected electrically at both front and
rear 6nds by thick copper or brass end plates, the joints be-
tween the bars and end plates being carefully soldered to mini-
mize resistance; rotors of this construction are known as
squirrel cage rotors. Power is fed into the primary winding
from the external circuit and the rotor is caused to turn, as
will presently be explained, by the heavy currents induced in
the rotor bars by the rotating magnetic field set up by the pri-
mary winding carried on the stator core. The rotor winding
is in no way connected to the external circuit; it carries no com-
mutator, brushes or slip rings. In fact, the induction motor
is simply a transformer with a short circuited secondary, this
secondary being free to move.

2. Theory of the Induction Motor. The operation of
the induction motor depends upon the fact that, when a mag-
netic field is dragged across a conductor, currents are induced
in that conductor, which themselves give rise to a secondary
field of such a direction as to oppose the movement of the gen-
erating magnetic field. In 1834, Lenz summed up the matter
by stating that "in all cases of electro-magnetic induction the
induced currents have such a direction that their reaction
tends to stop the motion which produces them." This very
important physical theorem can be demonstrated experi-
mentally, as explained in Chapter IV, by the apparatus shown
in Fig. 63, where a metal disc D is dragged into rotation by
the permanent magnet P, moved by hand circularly around
the periphery of the disc in a clockwise direction, as indicated
by the arrow, the disc following the magnet because of the
' '-action between the field of the permanent magnet and the

SIGNALS. 243

secondary field produced by the currents induced in the disc by
the primary field of the permanent magnet. Lenz's Law above
'quoted states that the reaction between two such fields tends
to stop the motion which produces them; therefore the cur-
rents induced in the disc tend to hold the permanent magnet
back* but, as the latter is being moved forward forcibly by
hand, the disc is itself dragged around. The disc corresponds
exactly to the rotor of an induction motor, and the rotating
field of the permanent magnet corresponds to the rotating
field produced by the induction motor stator.

, In the induction motor, the primary » or stator, winding is
grouped around the stator core in two or more independent
sets of coils, wound progressively in slots around the core,
and energized by two or more separate currents considerably
out of phase with each other. In the two-phase induction motor,
the currents in its two separate sets of stator coils are 90 de-
grees out of phase, while in the three-phase motor, the cur-
rents in its three sets of coils are 1 20 degrees out of phase with
each other, as regards the production of such polyphase currents;
it is obviously, possible, by placing on the armature of the ordi-
nary alternator, two or three sets of coils, one angularly ahead of
the other, to obtain respectively two or three alternating cur-
rents of equal frequency and strength, but differing in phase
by any desired degree. When the stator coils of an induction
motor are progressively energized by such currents, a rotating
field is produced, which drags the rotor around with it, just
as in the case of the disc illustrated in Fig. 65, and for exactly
the same reason.

3. Production of Rotating Field in the Induction
Motor. Most induction motors for signals operate on the
two-phase principle, and it is now proposed to explain just
how the rotating magnetic field is produced. One-half the
stator winding (one phase) of a two-phase four-pole induction
motor is shown in full lines B in Fig. 1 46, the other half A, ex-
actly like B, being omitted for the sake of clearness. In this
figure, the straight radial lines represent the conductors which
lie in the slots of the stator, and the curved lines represent the
connections around the outside of the stator core joining the
slot inductors. The complete stator winding is arranged in
two distinct circuits; one of these circuits includes all the con-
ductors mstrked A> ^nd this circujit receives current f rQm one

244

ALTERNATING CURRENT SIGNALING.

phase of a two-phase system, the other circuit, including all
the conductors marked B, receiving current from the other
phase of the two-phase system. The terminals of the B cir-
cuit are shown at tV. The conductors which constitute one
circuit are so connected that the current flows in opposite di-
rections in adjacent groups of conductors, as indicated by the
arrows.

The above windings A and B, assembled on the stator core,

are shown in Fig.
147, the small
circles repre-
senting the con-
ductors iii sec-
tion, conductors
carrying down-
flowing currents
being marked
with crosses
( + ). those carry-
ing up-flowing
currents with
dots, and those
no current at all
being left blank.
The action of
currents in these
bands.or groups,
of conductors is
to produce mag-
netic flux along
the dotted lines
in the direction of the arrows according to the Corkscrew
Rule, which, it will be recalled, states that, if the direction of
current flowing in a conductor corresponds to the forward
movement of a corkscrew, then the circular flux lines about
the conductor due to the current, turn about the conductor
in the same direction as the corkscrew turns to go forward.
« Suppose, BOW, that two currents, A and B, separated by a
phase angle of 90' degrees, as shown in Fig. 148, flow, respec-
tively, through windings A and B, in Fig. 147, these latter
being connected to the circuit, so that the current in coil A

Fig. 146. Half the Stator Winding for a 2-Pha0e,
4- Pole Induction Motor.

leads that in coil B, aa
indicated by the di-
rection marks witbin the
circles representing the
atator conductors. At
(a) in Fig. 147 is shown
the state of affairs when
the current in conductor
group A is B maximum
and th« current in
group B i» zero, cor-
responding to point 0
of Fig. 148. the dotted
lines in Fig 147 indica-
ting the direction of the
magnetic flux, deter-
mined by the Corkscrew
Rule above mentioned:
this fiua enters the rotor
from the stator at the
points marked N, and
leaves the rotor at the
ptnntg marked S. At
(b), one-eighth ofacyde.
or 45 degrees later, the
current In the B set of
conductor has increased,
and the current in the A
conductors has decreased
to the same value, so
that equal currents flow
in the A and B con-
ductor*, as will be
evident from the wave
heights at the end of the
first eight of a cycle in
Fig. 148; note that the
points N and S have
now „ moved over one-
MKteenth of the circum-
ference of th« atator

246

ALTERNATING CURRENT SIGNALING.

ring, from the positions they occupied in (a). Still, one-
eighth of a cycle later, as at (c) the current in B conductors
has reached the maximum value, and the current in the A
conductors has fallen to zero; the points N and S have again
advanced over one-sixteenth of the circumference of the
stator ring.

The above rotation of the points N and S shows that the
magnetic field is continuously revolving, the points (and the
field) making one complete revolution while the alternating
currents supplied to the stator windings are passing through
two cycles. In general:

n = ^ (.)

where n is the number of revolutions per second of the stator
magnetism, p is the number of poles, N and S, and/ is the fre-
quency of the alternating current supplied to the stator wind-
ings.

4. Speed, Slip and Torque. If n is taken to represent

the revolutions per
second of the mag-
netic field and n' the
revolutions per sec-
ond of the rotor, then,
when n = n', the
rotor and the mag-
netic field are turning
at the same speed
and the rotor would
be said to be running in synchronism. Under such cir-
cumstances, the relative motion between rotor and magnetic
field is zero; consequently no electromotive force is induced in
the rotor conductors and no current flows, so that no torque
is exerted by the field on the roton TTie velocity of the rotor
in an induction motor can therefore never equal the velocity of
the rotating magnetic field, since there must be relative mo^
tion between the rotor and the magnetic field to induce cur-
rents in the rotor tQ produce torque. Even when the motor is
running light, its speed cannot be synchronous. When load is
thrown on, the speed of the rotor will immediately fall, the
difference (,n-n^) of the speeds of the field and the rotor will

Fig. 1 48. Two Currents in Quadrature.

SIGNALS. 247

increase, and, therefore, the electromotive force induced in
the rotor conductors, the currents in the conductors, and the
torque with which the field drags the rotor, will all increase,
tending to bring the rotor up to speed again. It is to be re-
membered that the rotor is simply the short-circuited seconda-
ry of a transformer, and that, consequently, as explained in
Chapter VI, the secondary or rotor currents flow in such a
direction as to decrease the impedance of the primary, thus
permitting more current to flow into the primary or stator
from the mains as the load on the rotor increases. However,
the fact that this secondary, or rotor, field is in opposition to
the stator field results in some of the stator flux being forced
back, so that it does not link with the rotor conductors, but
shunts out, instead, through the air gap between the rotor and
stator; this leakage flux links only with the stator and gives
rise to a counter voltage in the stator to prevent the stator
current rising to correspond with the increase of load on the
rotor. If the whole of the primary flux were to link with the
rotor conductors, the torque would increase in exact propor-
tion to (n — n'), but, as a matter of fact, a larger and larger
fraction of the primary flux leaks around through the air gap
as the rotor is loaded, and, consequently, the torque increases
more slowly as (n — n^) increases.

As load is taken on by a motor, the rotor speed, therefore,
decreases in nearly direct proportion to the load, from nearly
synchronous speed at no load to about 92 per cent, in small
motors at full load. The difference in speed (n-n^), expressed
as a percentage of ssmchronous speed, is called the slip of the
motor. When an induction motor is overloaded, it draws
excessive current from the supply mains, and its torque in-
cresises up to a certain value of the slip; when loaded up to this
limit, the machine is unstable, and a slight additional load will
cause a great drop in speed.

5. Induction Motor at Starting. At the moment the
motor is connected to the mains, and when its speed is zero,
the relative speed of the rotor and the rotating magnetic field
is maximum. It is at this time, therefore, that the voltage
induced in the rotor conductors is greatest, and, in the case of
large motors, where the rotor conductors are bars of heavy
copper, enormous currents would be induced in the rotor

248 ALTERNATING CURRENT SIGNALING. "

which would result in the motor being burned up, if some
means were not provided to limit the rotor current, either by
temporarily inserting resistance in the rotor circuit, or by im-
pressing a smaller voltage on the stator during starting. In
small motors, such as used in signal work, such devices are not
necessary, for the reason that, due to the comparatively large
air gap used, the primary leakage flux is considerable; as pre-
viously explained, this flux links only with the primary, whose
impedance is thus prevented from falling below a certain safe
value, with the result that excessive currents do not flow
through either the stator or the rotor.

In this connection it is interesting to note that, due to the
primary leakage flux and the consequent presence of reactance
in the primary, or stator, circuit, the stator current lags be-
hind the impressed stator voltage, so that all induction motors
have, consequently, a low power factor, particularly at start-
ing.

In Chapter VI, dealing with transformers, it was explained
that, when the secondary of a transformer is open-circuited, a
certain current, known as the exciting current, flows into the
primary to magnetize the core and to supply no-load copper
and iron losses. Naturally, if there is an air gap in the core,
the exciting current will be larger than would be the case with
a solid core. In the case of the induction motor, there is a
similar exciting current, which will be comparatively large,
due to the necessity of providing a safe air gap between rotor
and stator, and, in signal motors, this exciting current con-
stitutes a large part of the total current; in fact, it will gen-
erally be found that the full load current differs little from
the no load current or the starting current.

6. Split-Phase Motors. The above discussion has been
worked out on the basis of a pure two-phase motor — one hav-
ing two separate primary circuits fed from two sets of mains
whose voltages differ in phase by 90 degrees. Were a signal
system to be equipped with straight two-phase signal motors,
three transmission wires would be required(one wire acting as
a common for the two phases), and, in many cases, this would
be objectionable on account of cost. ^ As a single-phase trans-
mission with two wires is used in most cases, it becomes neces-
sary to provide some means to divide the single-phase current
into two components separated by a proper piiase angle;, if

SIGNALS

249

induction motors are to be employed; the^ current flowing in
the mains must be split up into two components sufficiently
out of phase with each other, so that, when they are fed into
the windings of a two-phase motor, the Required rotating mag-
netic field will be produced.

Fortunately* this can be done, for, when a single-phase cur-
rent divides between two branches of a circuit where the ratio
of resistance to reactance is different in the two branches, a
phase-difference results between the branch currents. For,
example, referring to Fig. 149, M represents a two-phase in-
duction motor, with its windings A and B connected, respec-
tively, in series with resistance R and reactance X, these ex-
ternal elements and the stator wiQdings A and B being, there-
fore, connected in multiple
series across the single-
phase signal mains as
shown. The stator wind-
ings themselves generally
have a low inherent power
factor, and their currents
would naturally lag con-
siderably behind the volt-
age, as the windings are
carried on an iron stator
core and are, therefore,
highly inductive. In the
left hand circuit, however,
the resistance R is intro-
duced to bring the current Fig. 149. Split-Phase Induction Motor.
more nearly in phase with

the impressed voltage E, thus counterbalancing, in a way,
the inductive effect of the stator Winding A; on the other
hand, the reactance X is introduced in the right hand
circuit to help stator winding B to still further displace the
current out of phase with the impressed voltage E. For
example, if the total dead resistance in the left hand circuit
is 75 ohms, while the inherent reactance of winding A is 25
ohms, then the power factor (cos 0 ) of the total left hand
circuit is;

250 ALTERNATING CURRENT SIGNALING.

R 75 75

*~ ®^ = VR2 + X* " V752+25* " 79 " **•'* <^^
which corresponds to a lag angle 0 of only 18 degrees. If the
total resistance in the right hand circuit is 25 ohms and the re-
actance 18 75 ohms, then the power factor of that circuit
will be:

R 25 25

^ ®» " VR« + X« " V25* + 75'* " 79 = **-^' <'>

^hich corresponds to a lag angle 6 of 70 degrees. Finally,
therefore, the effective difference in phase between the cur^
rents in stator coils A and B is 71 ** - 18° = 53**, so that the
motor actually runs as a two-phase motor, with 53° instead
of the ideal 90° phase displacement.

In many cases, the reactance X in series with stator winding
B, Fig. 149, is alone used without the resistance R in series
with the A winding; at other times, the reactance X in series
with the B winding may be omitted and a resistance used in
series with winding A instead. In all such instances it will be
found that the designer has managed to secure adequate ph&se
splitting with one external element (either resistance or react-
ance) only, the natural or inherent power factor of the other
element being considered about right without external aid.

> It is not necessary that the two components be separated
by the full 90° displacement, for a rotating magnet field can
be obtained by means of any two alternating currents, what-
ever their phase angle, although the speed of the field may
not be absolutely uniform, and its intensity will not be so
great as would be the case with a pure quadrature relation-
ship. As a matter of fact, the intensity of the resultant field
will be found equal to the maximum value of either of the two
equal components multiplied by the sine of their phase angle.
To secure a given torque, each of the currents in a split-
phase motor will, therefore, have to be greater than those
required for a pure two-phase motor whose currents are in
quadrature; in the example given above, where the currents
in a split-phase motor are separated by a phase angle of 53 °
it will be found that these currents will each have to be
approximately 25 per cent, greater than those required with
ji full 90° displacement.

7. ^Iit-ph«se vertuB Pure Two-phase or Three-phase
Motors. The split-phase motors just described are. of
course, not ideal from a purely theoretical standpoint. They
are, however, very simple and reliable, and can be operated
from single-phase mains involving only two-line wires for the
transmission system-, for these reasons, they have generally
been adopted for signal operation, except where polyphase
currents are available. As will be explained in the next chap-
ter, it is sonietimes more economical to transmit power for
the signal system by a three-phase system requiring three-line
wires; in this case, of course, there is no necessity of using
spli t-phase motors, and they should not be em.'ployed in view
of the greater current they take.

S. Construct io
design of split-

of Induction Motors. A

F«. ISO. Indued

of signals is
illustrated in
Fig. 1 50. where

or shell, hous-
ing the statoT
and rotor is
seen at the left
of the photo-
graph, and the

phase- splitting device, serving also as a brake, at the right.
It will be seen that this brake coil is wound around a
vertical laminated core, pivoted at the bottom; this highly
inductive coil is connecied in series with the induc-
tance or lagging phase winding of the stator. so that, conse-
quently, the current in that winding lags greatly behind the
current in the other, or resistance, winding which is connect-
ed direcdy across the feeding mains. Normally, when no
current is flowing through the motor windiitgs, the brake
drops by gravity to the position shown in Fig. 150, but the
moment the motor circuit is closed by the signal control relay,
currentflovfsthroughthebrakecoil.andit picks up, closing!^

2i2 ALTERNAXrNG CURRENT SIGNA1.ING.

air gap at the top and pulling the brake pad at the same time
away from the bottom of the brake wheel, the brake pad
bcdTigcarriedbyancxtmsionon thebottomof the coreon which
the brake coil is wound. When the motor circuit ia opened,
the brake coil is de-energized, the brake core falls away, and
the pad comes in contact with the brake wheel so ae to pre-
vent the motor drifting. This element, therefore, serves the
double function of phagC'Splitter and brake. A sectional
side view of this motor is shown in Fig. 151.

SECTIONAL SIDE VIEW
Fie. 151. CioH ScctiuB of I nductian Signal Motoi Shown in Rf, 15a

When this motor, and others of similar deugn. is operated
aa a split-phase motor on 60 cycles, the heavy secondary re-
action at starting is liable to make the starting torque rather
small, unless one is willing to put considerable power into the
motor at that timei in order to avoid this, the rotor is often
connected to its shaft tlirough a simple centrifugal clutch, which
allows the rotor to get up speed and cut down the secondary
reaction before the motor takes on its load. With this in
view one of the end plates of the rotor is provided with two

SIGNALS. 253

short steel studs placed diametrically opposite, each car-
rying a short centrifuge arm, the outer, or shoe end
which engages with a pressed steel shell, or drum, pinned
to the rotor shaft; when the rotor speeds up at starting, it
spins free on the shaft for the first few revolutions. Thus,
even though the starting torque is small, the motor finally
will carry its load with a very moderate amount of power.

COMMUTATOR MOTORS.

9. Elements. The alternating current commutator mo-
tors used for the operation of signals are, without exception ,
of the series type, and, in their construction and electrical
characteristics, they are, in many ways, similar to the direct
current series motors so familiar to every signal man. The
elements of the alternating current series commutator motor
are, first, the laminated field core with its energizing coils, and*
second, a wire wound armature carrying a commutator, the
armature and field being connected in series through the
commutator and its brushes.

10. Theory of the A. C. Series Motor. Since a direct
current series motor , such as is generally used for the operation
of D. C. signals, does not reverse its direction of rotation when
the current is simultaneously reversed in its field and arma-
ture windings, it might be expected to run when supplied with
an alternating current. As a matter of fact, this is the case
when the field and armature cores are well laminated to avoid
excessive eddy currents, and the electric and magnetic cir-
cuits are so designed as to keep the self-inductive reactance
within reasonable limits, for it must be remembered that the
flow of alternating current through the field and armature
windings gives rise to induced voltsiges in these elements,
purely aside from the counter-electromotive forced induced in
the armature conductors by their rotation through the field.

In the case of the D. C. series motor, it is common to make
the fields strong to prevent skewing of the field flux, with re-
sultant poor commutation, while the armature is made mag^
netically weak for the same purpose, and also in order to re-
duce the self-inductance of the coils under commutation to a
minih.um. In the A. C. series motor, on the contrary, the
field is made magnetically weak to reduce its self-inductance

154 ALTERNATING CURRENT SIGNALING.

to a minimum and to prevent too great a voltage being in-
duced in the armature, with resultant: Sparking. To secure
adequate torque, the armature is made magnetically strong.

The greatest difficuTty which has been encountered in the
design of A. C. series motors has resided in the unavoidable
voltage produced in the rotating armature coils at the moment
theyareunder and are short-circuited by the brushes, this volt-
age being due to the cyclic variation in the field magnetism.
At the instant when the field flux is a maximum, no current
is induced in the short-circuited armature coils, due to its
change, but the coils enter the condition of short-circuit bear-
ing maximum line current; and, when the field flux is zero
a maximum current is induced in the short-circuited armature
coil, but the line current is zero. The short circuited coils
being, with respect to the field windings, in effect, trans-
former secondaries of very low resistance, the short circuit
currents become very large. When a brush passes form one
commutator segment to the next, as the armature rotates,
the electromotive force is short-circuited through the brush
which completes the connection between segments. The cur-
rent through this short circuit is likely to be of large volume
and produces an excessive heating of the brush, the segment
and the coil. Moreover, and what is of greater importance,
the rupture of this heavy current produces destructive arcing
at the brushes, which roughens and spoils the surface of the
commutator.

11. Construction of the A. C. Series Motor. The
motor illuBtrated in Fig. 152 illustrates the general ccoutruc-

H(. 152. A. C.S«W(Commut*tor Signal Motoi.

SIGNALS. 255

tion of motors of this type, it being evident, from this draw-
ing, that, in appearance, the A. C. series motor is almost ex-
actly like the D. C. series motor. In Fig. 152, a brake coil-
connected in multiple with the armature and field windings,
actuates a brake niechanism, whereby, when the motor cir-
cuit is opened, a leather pad carried by the brake armature
comes into contact with a wheel pinned to the motor shaft,
thus preventing the motor from overrunning or drifting.

12. Application of A. C. Series Motors. Series motors
at one time were rather favored by some engineers because of
attractive power economy; the A. C. series motor consumes,
possibly, not more than 60 per cent, of the power of a single-
phase induction motor of equal output. When carefully de-
signed, series motors work out fairly well. The sparking at
the brushes and the roughening of the commutator, men-
tioned above, are not very serious matters in the case of a
signal where the motor is not forced to rotate backward when
the signal, is traveling from proceed to stop, but would be in-
tolerable in the case of a drift backward spindle type mech-
anism. A. C. series motors have, occasionally, been used
with signals of this latter type, but have not proven satisfac-
tory, because the roughening of the commutator, due to
sparking, sometimes seriously retards the backward move-
ment of the mechanism from proceed to stop, simply because
considerable friction is introduced at the place where it does
the most harm — the commutator which travels at the high-
est speed.

13. Comparison between Induction and Series
Motors., Without question, the induction motor is the
simplest and most easily maintained of alternating current
motors. It is free from commutators and .brushes, and all
the troubles which are inherent with such devices when used
to break heavy alternating currents at a high voltage. The
ability of the squirrel cage induction motor to withstand
rough treatment and heavy overloads is proverbial. Well-
designed induction motors for signal operation can even be
"blocked," or held stationary indefinitely with full voltage
across their windings, without injury, whereas, under similar
circumstances, a series motor would bum up.

From the signal engineer's standpoint, the chief objection

256 ALTERNATING CURRENT SIGNALING.

to the series wound motor is the commutator. This is espe-
cially true with signals so designed that a motor rotor rotates
while the signal arm is changed from proceed to the stop indica-
tion. The friction of the brushes upon the commutator re-
quires a large extra counterweight on the spectacle casting.
This not only means extra energy for carrying the extra
weight, but also means unnecessary wear to the mechanism;
first, on account of the inertia to be overcome in starting the
signal from the stop to the proceed indication, and second, on
account of the wear of the mechanism due to the momentum
of the motor rotor, which accelerates very rapidly with the
downward movement of the spectacle casting in carrying
extra heavy weight. Brushes require constant attention, said,
in the case of a broken brush, or poor contact, a signal failure
results. Also, sparking of the commutator tends toward car-
bonization, which necessitates careful watching and special
attention to the insulation between the segments of the com-
mutator. With the induction motor, all of this and kindred
troubles are eliminated.

As regards the matter of relative power economy, a repre-
sentative type of series motor takes 165 watts against 270
watts for an inductive motor. Now, if there were four trains
per hour passing a signal for 24 hours each day, and it required
four seconds to dear the signal, then the series motor would
consume 6,424 watt-hours per year, while the induction motor
would take 10,512 watt-hours. The differchice, 4,088 watt-
hours per year, at two cents per kilowatt hour, would make
a difference in the cost of current for clearing each signal 8.2
cents per year. This gain in economy would hardly seem to
justify the use of the series motor, except in special cases.
The real cost for energy for the operation of a signal is not
the cost of clearing the signal, but the cost of the energy to
hold the signal at the proceed indication; this amount would,
of course, be constant, regardless of the type of motor used.

It is in its influence on the size of the transmission line that
the series motor is most attractive. Due to the low current
it requires, as compared with the induction motor, the size
of the transmission wire may be made smaller for the series
motor than for the induction motor. The size of the trans-
mission wires is regulated by the maximum current they have
to carry, and, of course, this maximum condition arises every

SIGNAUS.

257

time all the signals have to be cleared at once, as would hap-
pen, for example, after some momentary interruption at the
power house. In practically all cases, however, the tem-
porary drop in the transmission caused by a system of induc-
tion motors all running at once may be compensated for by
raising the voltage at the power house for a few seconds until
the signals have latched up and their motors have stopped.

HOLDING DEVICES.

14. Kinds. Briefly, slots or holding devices for alter-
nating current signals may be divided into two classes: (a)
Tractive Magnets with shading bands, and (b) Induction
Slots.

15. Tractive Magnets. If a laminated iron magnet
core, say of the horseshoe p>attem as illustrated in Fig. 153,
is magnetized by an alternating current flowing in the coils
wound around the core, then a magnetic flux in phase with

FERRULES

Fig. 1 53. Tractive Type Slot Magnet.

the current will, naturally, be set up in the iron core. As the
current in the coils rises and falls, so will the flux rise and fall
correspondingly and in such a manner that, when the current
passes through the zero point of the alternating current sine
wave, so, also, will the flux pass through zero. When the
flux is zero, the pull, or tractive, effort on the armature op-
posite the poles is also zero. Consequently, the pull of such
a magnet is pulsating and the armature rattles back and forth
against the pole faces with a humming noise.

258 ALTERNATING CURRENT 5IGNAUNC.

If. now. a pair of heavy copper femilea, or shading bands
are set into tKe pole faces so that half of each pole end is sur-
rounded by a band, as shown by the heavy black lines in Fig.
153. then currents will be set up in the shading bands by the
alternating magnetic flux; necessarily, the currents in these
shading bands will lag just 90° behind the flux, because it is
when the rate of change of the main flux Is greatest (when the
main flux is passing through zero) that the induced currents
are the greatest. The currents induced in the copper shading
bands exert a counter magnetizing ftirce acting in a direction
to reduce the increase in lines leading through the shading
cml. Thus, the flux increases rapidly over the "unshaded"

Fi(. 1 34. Slot Arm ProvidfM] with Slot ConUct.

portion of the pole, while that in the shaded portion is re-
larded and lags behind the main flux. Or. again, the cur-
rents induced in the shading coils may themselves be con-
sidered as the seat of a secondary magnetic field, which is zero
when the main flu^t is maximum, and is maximum when the
main flux is zero. It is. therefore, apparent that some flux is
always passing from pole pieces to the armature, and. !n that
way. a continuous tractive effort, or pull, is maintained.
Slot magnets of this type are used in signals of the Style "B"
and the Style "S" types.

In many cases, such a slot magnet as the above may coa-

SIGNALS.

259

veniently be used also, as a line relay when equipped with the
proper contacts. For example, where line control for distant
signals is used, a line relay usually has to be provided at the
controlled signal to close the distant motor and slot circuits.
The design shown in Fig. 1 54 illustrates how such a line relay
may be dispensed with. The distant slot armature carries
at its lower end a small insulating block supporting a carbon
roller about f ' in diameter in such a manner that, when the
slot magnet is energized from the line and the armature
is pulled forward, it closes the circuit between the Y-
shaped ends of the two contact springs supported on insula-
tions carried at the bottom of the slot magnet core frame; the
terminal posts for these contact springs are seen di-
directly under the slot magnet in Fig. 1 54. When the signal
indicates slop and the slot arm is down, the pair of swinging
brass counterweights immediately at the left of the armature
hold the armature away from the magnet poles, so that the
contact is held open. This device is called a slot contact;
it takes the place of an ordinary line relay in controlling the
motor circuit of the slot arm and signal in question.

16. Induction Slots. Holding devices of this kind,
working on the induction principle, consist of a primary, or
stator, element and a secondary, or rotor element. They are
mainly used at
present on spin-
dle type top post
signals of the
T-2 type herein-
after described.
Their theory of
operation will be
readily grasped
from a study of
Fig. 155, which
shows an eight
pole laminated
stator H carry-
ing 8 coils, C
one over each
pole, and which,
when energized. Fig. 155. Induction Slot.

260 ALTERNATING CURRENT SIGNALING.

give rise to fixed magnetic fields flowing between poles in
the direction of the dotted lines. The rotor D is also
laminated and carries 8 copper bars B arranged sym-
metrically about the rotor, these bars being soldered into
massive end plates, just as in an induction motor.
Furthermore, rotor D is pinned to the motor shaft so
that, when prevented from rotating, the semaphore shaft,
attached to the motor shaft through a train of gears,
is in turn held locked, and in this manner the signal may
be held in the proceed position after it has once been cleared
by the motor. As long as there is no torque on the shaft,
the bars of the slot rotor D (when the stator is energized)
will rest directly under the middle of the pole faces of the
stator core, but, when the signal is cleared and load comes
on the slot rotor D through the motor shaft, then bars B
come within the field of the stator windings, with the
result that currents are induced in the slot rotor bars; these
secondary currents, of course, flow in such a direction that the
field which they give rise to reacts on the main stator field in
such a direction as to thrust the rotor bars back out of the
field into which the torque of the motor shaft had forced them;
this is in accordance with Lenz's Law stating that in all cases
of electro-magnetic induction, the induced currents have such a
direction that their reaction tends to stop the motion which
produces them. In fact, the rotor bars will be forced just far
enough within the stator field to have just enough current in-
duced in them to balance the torque brought on them by
the motor shaft.

Induction slots are very simple and strong in their construc-
tion, require little maintenance, and are not liable to be stuck
by congealed moisture or gummy oil, since there are no surfaces
to come in contact, the slot rotor D simply rotating in the bore
of the stator, the two being separated by a liberal air gap.

SIGNAL LIGHTING.

17. Lamp Bodies. Lamp bodies for electric lighting for
signals are generally much simpler than those for oil lighting,
as the top draft or ventilating feature of the oil lamp and the
oil font are, of course, unnecessary in electric lighting; some
of the conunercial types of lamp body for electric lighting

consist simply of a cylindrical sheet iron caaiiiK provided at
the top with a sheet iron cap. the incandescent bulb being
supported on the inside of the lamp body by a wooden or
porcelain block carrying pony sockets. Another well known
type of lamp, somewhat more accessible tham that previously
described, consists of two light iron castings, as shown in Rg
1 56. one fitting on top of the other, the lower one carryiikg the
terminal block and lamp sockets.

Fiff. 1 56. Semiipbore Lamp for Signal Lighdng.

18> Carbon veifu* Tungsten Lamps, In the early
days of electric lighting for signals, carbon lamps were gen-
eraUy used, but, due to the low economy of the cartxin lamp,
it has now been generally replaced by the lamp with a tung'
sten fjlament; for example, a 2 C. P. 1 10 volt carbon lamp re-
quirct about 1 4 watts, whereas the tungsten lamp takes only
2^ watts; it is not surprising, therefore, that the carbon lamp
has been superceded by the tungsten lamp in signal lighting,
as elsewhere. The economy of the tungsten lamp results from
the fact that the metal filament can be worked at a very high
temperature, and consequently, the filaments are rather smaQ
in cross section as compared with the carbon lamps; in fact,
the filament of a 2 C. P. tungsten lamp for 110 volt work
would be too fragile to be serviceable, although carbon lamps
can be obtained for almost any vdtage. In order ti

262 ALTERNATING CURRENT SIGNALING.

~- _ _ - — t

secure a strong, sturdy filament, most tungsten lamps used
for signal lighting are made for a normal voltage of 1 0 or 12.

19. Number and Candle Power of Lamps. In most
cases, two incandescent lamps are used in each lamp body,
so that their lives will overlap, thus insuring that one lamp will
be always burning; it is, of course, highly important to keep
at least one light always burning to maintain the indication.
Some very careful work has recently been done with tung-
sten lamps, however, and at present the life of the tungsten
lamp can be predicted with considerable certainty within 2
per cent, of its actual performance. It is the general practice
to use two 2 C. P. lamps back of each lens, although two
1 C. P. lamps would give sufficient light for good indication,
if a 1 C. P. tungsten lamp were commercial, which, however,
is not the case, as the filament would be too small and fragile.

20. Life of Lamps. Lamp manufacturers generally
guarantee a life of at least 1000 hours for tungsten lamps, but,
in actual practive, it is generally found that the life of the
lamp will be much longer than is indicated by the manufac-
turers' guarantee; as a matter of fact, most tungsten lamps
will have a life varying between 1 700 and 3000 hours, if burned
at full normal voltage.

However, it is a well known fact that the life of a lamp is
enormously increased if the lamp is burned considerably
below normal voltage, and, consequently it is the general
practice to bum 12 volt signal lamps at 10 volts; at this volt-
age plenty of light is secured, and it is not unusual for a lamp
to bum from eight months to a year.

F«. I}7. StTl> '

THE STYLE B SIGNAL

I. Description, The style B ngntd ia, without doubt,
the best known signal in America, there being some 60,000 of
them. A. C. and D. C. in service. A detailed description is,
therefore, unnecessary for American readers, but for the in-
formation of foreign engineers, it will perhaps not be Out of
place to state that the machanism consists of a motor, located
at the lower left hand comer of the front view shown in Fig.
158, driving through a train of gears a vertical chain carried
at top and bottom by sprocket wheels, as illustrated at the
eztremc left of the f rent view. Thechain, tuminginacounter-

Rg. I5S. CroH Scclion Style "B" Two-Poaidciii A. C. Siinal Mccfaulnri.

clockwise direction, carries two projecting roller studs, evenly
spaced along its length, one of which as it travels upward,
engages a forked head projecting from the slot arm. to which
latter the up and down rod of the signal is attached, the slot
arm being the member extending downward diagonally from
light to left. The slot arm carries the slot magnet or holding
device, which, when energized, holds locked through a simple
•ystem of levers, the forked head carried at the extreme left.
When the chain Toller engages this forked head, the slot arm

266 ALTERNATING CURRENT SIGNALINa

is lifted upward, turning on a shaft at its right hand end. As
the slot arm is lifted, the up and down rod rises with it. and
the motion continues until the signal is cleared and the chain
roller, arriving at the end of its travel, passes out from under
the forked head, leaving the latter to rest on a pair of hooks,
or fingers, which slip under it at the end of its strokei Mean-
while, the head of the slot arm has pushed open the circuit
breaker shown at the upper laf t hand comer of the mechanism;
thus automatically opening the motor circuit; immediately
the current is intemioted. the motor is quickly brought to
rest by the brake shown in Fig. 130; this half revolution of the
chain brings the second roller around below the bottom chain
sprocket ready to lift the slot arm the next time the signal is
to be cleared; it will be evident that, were the 'motor not
|>romptly stopped, the roller would overtravel and the chain
would have to make another half revolution before the next
chain roller were in the engaging position.

When the signal control relay opens and the slot magnet
is thereby de-energized, the slot armature is immediately
thrust away from the poles due to the thrust transmitted from
the up and down rod through the slot arm levers, the armature
thus unlatching or unlocking the forked head; this latter is not
rigidly attached to the slot arm, but is pivoted thereon, so
that due to the heavy downward thrust of the up and down
rod attached to the semaphore, the forked head turns upward
about its pivot, slips otf the hooks on which it hung, and the
whole slot arm drops instantaneously by gravity down to. the
position indicated in Fig. 158. To prevent the mechanism
being jarred or injured by this downward drop of the slot
arm, the latter actuates a piston working inside the cylinder
shown at the upper right hand comer of the cut, the compres^
sion of air in the cylinder on the up-stroke of the piston serv-
ing to ease the downward movement of the slot arm; to
regulate the degree of compression, the buffer cylinder is pro-
vided at the top with an adjustable escape valve or vent.

It is to be noted that the backward movement of the signal
from proceed to stop is in no way retarded, except by the com-
pression of air in the butfer. There is no compression until
tlie slot arm has unlatched and has started to 4ra>p dowa-

SIGNALS. .. . S - 267

ward; in practice, it is found that the slot arm drops imme-
diately through about three^iuarters of its stroke before com-,
pression becomes effective. The Style B mechanism, there-
fore, differs radically in principle from spindle type top mast
mechanisms, where the motor acts more or less as a buffer,
and has to be turned backward at a rapid rsitp when the signal
is returning from proceed towards stop. The proverbial safety
of the Style B signal is directly due to the fact that the back-
ward movement of the si^^nal from proceed to stop is absolute-
ly free and unrestricted; there can be no false clear failures
resulting from dirt clogging the motor air gap, as the motor is
entirely disconnected during the backward stroke.

2. Motor and Slot. The Style "B" A. C. signal may be
provided with either an induction motor or a seies commu-
tator motor; for reasons previously explcuned, the indue ion
motor is recommended and the mechanisms illustrated in Fig.
157 and 1 38 are so equipped. The slot is of the tractive mag-
net type with shading bands, as described in connection with
Fig. 1 53. The motor and slot can be wound for any commer-
cial voltage or frequency, single or polyphase, the standard
voltage being 1 10 and the frequencies 25 and 60.

3* ' Three-position Signal. The mechanism shown in
Fig. 138 has but one slot arm and is designed to operate a
one-arm two-position semaphore through either 60^ or 90 **
in either the upper or the lower quadrant. Where home and
distant signals are to be operated on the same mast, the mech-
anism is simply provided with two independent slot arms, one
for the home blade and the other for the distant, one motor
serving for both blades as the two are never cleared simul-
taneously. In the three-position signal (Fig. 159) two slot
arms are likewise used, the up-and down rod being provided
at the lower end with a small rotating pinion meshing between
two vertical toothed racks projecting upward between guides
from the slot arms. Each slot arm lifts a rack and when the
front slot arm reaches the top of its stroke, its rack has carried
the pinion to lift the up and down rod through half its total
travel, thus bringing the semaphore to the 45 **, or caution
position; when the back arm slot lifts, it completes the upward
stroke of the up-and-down rod, so that the signal indicates
90®, or full proceed.

ALTERNATING CURRENT SIGNALING.

Rs. 159. Style "B" Thiee-PoHtioa A. C. Sliniil Machuidu.

4. Circulti, The complete circuit diagram for the Stylo
"B" signal, working in either three pogitiona cm- aa a home and
distant signal, is covered by Fig. 160, the circuit breakers at
the left (those cariied on the insulating base at the upper left
hand comer of the mechanism in Fig. 1 59 and operated by th«
slot arm) being shown in positions corresponding to the »lop
indication of the aignal blade, both slot arms A and B being
shown. When slot arm A is cleared it opens at the top of it)
stroke, circuit breaker I and cIobcb circuit breakers 2 aitdJ. so that
when the 90° control circuit is complete the motor will dear
slot arm B through circuit breaker 5. When the signal ia
roatroUed directly by a three-pontion track relay it must
be remembered that when the relay shifts from one poatiofi

SIGNALS.

269

5f tf>(D

M
<

t fi

M H

O
U
Q.

K.
Ul

y
I

u
o a

o S
u c

" z

. I'

z (0

<•<:<

H«2
S

^ o
u

/?/>

< tf)

-V V-

AS oaxy«i3dO

8U3110tfXN09 XinOMlQ

Fig. 160. Circuits for Home and Distant or Three- Position Style "B" A.

A. C. Signal.

270

ALTERNATING CURRENT SIGNALING.

Oreui* Con1t-oN0r opuratmd by-
S/of Arm A Sfot Arm B

(b ^

TTTT

■EE

F
^

« •

!4. "* ^
<i» ^ ^

Fig. 161. Circuits for Home and Distant or Three-Position Style "B'*
A. C. Signal with Slot Contact on Distant Arm.

SIGNALS.

271

to the other, the control circuit is momentarily interrupted,
and in order to prevent the caution slot from "kicking otf, "it is
customary to feed the latter direct from the transformer over
the points of a slow acting relay, the relay itself being con-
trolled from a 43 ^ contact of the three-position track relay.
The slow acting relay may be either of the vane type or of
the polyphase type; the polyphase is naturally slow acting on
account of its geared movement and the vane can be made
slow acting by adjusting its contacts so that they will not open
until the vane has fallen nearly to the bottom of its stroke.
Thus while the slow acting relay is de-energized during the
reversal of polarity of the track relays, the signal circuit is
kept closed. It is obvious, of course, that a slow acting re-
lay is not necessary when the signal is controlled by separate
two-position track and line relays, such as would be used in a
line control circuit for the clear or distant indication.

Where line control for the clear or distant indication is em-
ployed the slot contact device illustrated in Fig. 154 and de-
scribed on page 258 of this chapter may conveniently be
used, as it eliminates the necessity of a line relay. Fig. 1 6 1
illustrates this application, clear or distant slot arm B acting
as a line relay to close the slot contact immediately to its left
to control the motor circuit. Slot contacts of this type have
seen a very extensive application and their dependability has
been thoroughly proved.

ELECTRICAL CHARACTERISTICS OF STYLE "B" A. C.

SIGNALS.

Signal

Fre-
quency

Voltage

Induction
Motor
(Single-
Phase)

Blot

Clear-
ing
time
Sec.

Nor-
mal

Min-
imum

Amps

Watts

Amps

Watts

2 pos. 60"

3 pos. 90'

25
60
25
60

110
110
110
110

90
90
90
90

2.1
2.3
2.2
2.4

120
130
125
135

0.32
0.45
0.64
0.90

11
15
22*
30*

*Total with both slot arms energized.

272 ALTERNATING CURRENT SIGNALING.

^ ^

Fig. 161b. Ons Aim Styla "B" ThiH-Porition Upper Qiudnnt Cioonil
Pom SigiuU. The 5i(ii>i >t the Right it PrDvided with ■ Doubla Cua.
■he Lowu Hail c[ which May be UmI foi Housni Tiuk Trualotiv
en. Impetluicee ore £xtni R«l«y*>

178 ALTERNATING CURRENi SIGNALING.

F«. 164. Slyln "T-Z" A. C. SjmL

THE STYLE T-2 SIGNAL.

1. Description. This signal is of the 8[nndle or top mnat
type, tlie motor, located at the top of the mechanism, as
shown in Fig. 1 64, driving the semaphore shaft directly
through a train of light but strong drop forged oil-tempered
gears running on roller bearings, the motor itself running on
ball bearings. The motor and slot. Or holding, device are
both housed in the same cylindrical iron case illustrated jn
the photograph. The circuit controller, projecting outward
from the bottom of the mechanism, consists of two porcelnin

•> SeclKHi of "T 2" A. C. Thtee-PoHtkm SifiuJ Macluiuini.

MO ALTERNATING qjRRENT SIGNALING,

blocks carrying contact fingera extending inwsnlly and rub-
bing on tdrcular brasa segmenta. inaulated from each other
by moulded buahiogs and carried on the circuit controller
■haft. These detaila will, perhaps, be more easily undar-
stood after an inspection of Fig. 165.

2. Motor and Slot. The motor and slot are both of the
induction type; a full eiplanaticin of the principle on which
the latter worlia will be found in connection with Fig. 15S,
from which it will be noted that the slot rotor is locked mag-
nedcally and prevented from rotating by currenta induced in
ita conductors by the slot stator when the latter is energized
by the control relay. The detail parts of the motor and slot

Fi(. I«6. Motor and Slut PuU sf ■-T-2" 3!giul.

are illustrated in Fig. 166, where 39 and 40 are the slot and
motor atators, and 19 and 20 are the slot and motor rotors;
respectively, (carried on the same shaft); 60 is the caae, or
shell, housing the above elements, and 41 is the front pla.t«
closing the case and containing at ita center a ball bearing,
in which the front end of the motor and slot shaft runs; the
front plate 41, it will be noted, is provided with tranaparoit
windows 42, permitting on ingpectkok of the parts inside the

The assembled motor and slot are clearly shown at the ti^
€)l Fig. 165. 19 and 20 being, reapectivdy. the alot and motor

SIGNALS.

2ftt

Resist4nce
Winding

React ance
-Winding

Slot

fVW\AA^

Resistance

{ 6 ;

Auxiliary j

Circuit Controller ^

^Qmjnon
i [49 deg^ Control

Fif. 167. Wiring Diagram for "T-2" Three-Position A. C. Signal.

282 ALTERNATING CURRENT SIGNALING.

rotors, as before. The motor rotor drives the shaft through
a toothed ratchet 13 on the clearing stroke, but when the
semaphore is traveling backward toward stop* the motor rotor
is disengaged from the shaft through the ratchet, and, when
the blade reaches the stop position, the rotor spins free on the
shaft, thus relieving the mechanism from the shock of ab-
sorbing its momentum. The motor can be wound for either
single or polyphase operation; when required to run single-
phase, phaise splitting is accomplished through the insertion
of resistance in one of the windings, this resistance consisting
of a fireproof spool wound with bare wire and located imme-
diately under the motor in Fig. 165; the conductors of the
other winding are laid in peculiarly formed slots in the stator
core, so that the inductive reactance of this winding is ex-
tremely high. Thus, even though, for safety's sake, a large
air gap is provided between stator and rotor, excellent phase
splitting permits of low power input, considering the size of
the air gap used.

3. Circuits. The circuit arrangement for a three-posi-
tion signal controlled off a single-phase circuit by a three-
f>o8ition relay, is shown in Fig. 167.

Contact segment 2 controls the motor circuit for the proceed
f>osition, and segment 3 controls the circuit for the caution
position. Segment 4 controls the slot circuit. An auxiliary
cuit controller attached to the outward end of the regular cir-
circuit controller shaft, as shown in Fig. 165, is used to pro-
duce a retarding torque through the motor when the sema-
phore arm is returning from the proceed to the caution posi-
tion and thus assist in bringing the rotor of the slot to a stop
so as to enable it to hold at caution. This controller, (D, Fig.
165), consists of a contact segment 18, and a vertical arm 16,
which carry two movable contact fingers 15 and 17, at the
lower end. This arm has a limited horizontal motion between
two stop screws, which enables the circuit to be closed at 1 5,
in one direction, and at 1 7, in the other direction. By a fric-
tion drive, contact 15, is held closed when the semaphore arm
is being moved toward the proceed position.

When energy is supplied to the 45 degree control wire, it
to the motor through contact segment 3, and wires C
O. Tlie circuit of wire C includes the resistance coil for

SIGNALS. 283

phase splitting. The motor winding connected with this coil
is known as the resistance winding. The winding of the
motor connected to wire D is known as the reactance winding.
The windings connected to wires C and D make connection
to common.

The holding circuit in the caution r>osition is through wire
A, contact 15, wire F, contact segment 4, and wire G, through
the slot winding to common. When the 90 degree control
circuit is energized, the motor circuit is completed through
wire H, and contact segment 2, in the manner described above.
The holding circuit in the proceed position is through wire I»
contact segment 4, and wire G, to the slot coil.

When the semaphore arm is returning from the proceed to
the caution position, the auxiliary circuit controller is brought
into play. In this case contact 15 is opened and contact 17
is closed, and the circuit to the motor from the 45 degree con-
trol wire is completed through the contact fingers bearing
against contact segment 18. Segment IS has an adjustment
between the positions corresponding to 42 degrees and 52 de-
grees of the stroke of the semaphore arm and is arranged to
close the circuit of the motor when the caution position is
reached, in a manner tending to produce rotation in a direc-
tion to move the semaphore arm towards the proceed position
again. Tliis has the effect of stopping the mechanism and
the first movement of the mechanism tending to drive the
semaphore arm towards the proceed position opens the motor
circuit at 17, and closes the slot circuit from the 45 degree
wire at 15, thus enabling the slot to hold in this f>osition.
The mechanism wiring for a two-position signal is somewhat
simpler, contact segments being necessary only to open the
motor circuit and close the slot circuit. No auxiliary circuit
controller for bufHng is needed for the two-position signal,
because, naturally, the return movement of the semaphore
arm does not have to be slowed up so that the slot may hold
at caution* Due to the mass inertia of the moving parts no
slow acting relay is required to bridge over the interval dur-
ing the reversal of the three-r>o8ition control relay.

4. Characteristics oi Style T-2 A. C. Signals. As this
signal is of the drift-backward type, especial care has been
taken in its design to eliminate in every possible way the ele"

284

ALTERNATING CURRENT SIGNALING.

ment of friction, so that the semaphore will be perfectly free
to drop from the proceed toward the slop position. Hence:

(a) The gears travel on roller bearings;

(b) The motor runs on ball bearings:

(c) The motor is of the induction type and is, therefore,
free from commutator friction, which would have to be con-
tended with if an A. C. series motor were used.

(d) The slot is also of the induction type and is free from
any contacting surfaces or latching devices; its rotor, like the
motor rotor, turns in a large air gap and is locked or held only
by the currents induced in it, over this air gap, by the stator
magnetic flux.

ELECTRICAL CHARACTERISTICS OP STYLE "T2"

SIGNALS.

Fre-
quency

Voltage

Induction
Motor
(Single-
Phase)

Slot

Clear-
ing

Signal

Nor-
mal

Min-
imum

time

Amps

Watts

Sec.

Amps

Watts

3 pos. 90^
3 pos. 90**

25
60

110
110

92
92

2.3
3-. 3

197
230

0.44
0.72

13
13

10
9.5

SIGNALS.

285

DIAMETER OF
ROUNDEL a^V

Fig. 167b. One Arm and Tvro Arm Upper Quadrant Tkree-Pontion "T-2"

Top Mast Signals.

286 ALTERNATING CURRENT SIGNALING.

SIGNALS.
Part II.

Light Signals.

1. Application. Light signsJs for day and night indica-
tion have been employed for a number of years in the subways
of New York, Boston and Philadelphia, and out in the open
on the Brooklyn Bridge, Williamsburg Bridge, and the Penn-
sylvania Terminal area in New York. More recently they
have seen a much broader application on the interurban elec-
tric roads. Their first and greatest advantage is, perhaps,
their comparatively low cost, and, next, their simplicity due
to their freedom from all moving mechanical and electrical
parts. The indication, especially the red siop^ will almost
equal the semaphore, considering the oftentimes poor back-
ground of the latter, and in the dusk should be superior. The
important indication, the red stop, is the most pronounced,
and by proper hooding of the lens, can be made effective in
the face of sunlight, which obviously will strike the lens only
when the sun is low on the horizon and its rays are conse-
quently weak. By the use of a well designed lens, properly
hooded from the sunlight and well illuminated by incande-
scent lamps of adequate candle-power, the light signal can
be made perfectly satisfactory for high speed service.

2. Hoods and Backgrounds. The hood above men-
tioned is generally a deep sheet iron cap; when seen from the
distance, an illuminated lens, so hooded, has the appearance
of being set in a dark well. A further contrast is secured by
providing the case enclosing the lenses with a flat sheet iron
background, this extending in a vertical plane at right angles
to the track from the sides of the signal case. If the signal
could always be located so that it would gave a dark back-
ground, such as that afforded by trees or a hill, the shield just
described would probably not be required, but, when the sig-
nal is set up against the sky, the shield provides the necessary
contrasting background. Practically all light signals for
outdoor service are. therefore, equipped with both hoods and
backgrounds, as will be evident from the photographs in the
following pages.

SIGNALS. 287

3. Tsrpes. Light signals may be divided into the follow-
ing classes:

I — Light signals for outdoor service:

(A) Color light signals giving indication by colored lenses.

(B) Position or beam light signals giving indication by

the illumination of one or more rows of uncolored
lenses spaced angularly to represent the successive
positions of a corresponding semaphore.

II — ^Light signals for subway service:

(A) Color light signals giving indication by colored lenses.

ALTERNATING CURRENT SICNAUNG.

COLOR SIGNALS—OUTDOOR SERVICE.
MODEL 12 LIGHT SIGNAL.

1. Rangc'and Application. The above usdbI is pro-
vided Vfith one green and one red lens, each 5f " in diameter,
intended to indicate proceed and slop, respectively. Under
the worst conditions, with the sunlight shining directly on the
lenses, the indication is effective up to approximately 1500
feet; at other times of the day, when the conditions for visi-
bility are more favorable, the above limit ia increaiied about
50 per cent. This signal is the simplest of the Ught signals,
and is intended primarily for use as en intermediate signal
on intenirban roads, where the block lengths do not require
greater range of visibility than above given.

2. Lenses and Lamps. The lenses are of the Frasnd
optical pattern. Each lens is ordinarily illuminated with two
20 watt 1 1 0 volt tungsten lamps connected in multiple.

Fv. 169. Model 13 Lifhi Sipult. CWiliiwl, Aatiach and EHMcn R. R,

ALTERNATING CURRENT SIGNALING.

COLOR SIGNALS— OUTDOOR SERVICE.
MODEL 13 LIGHT SIGNALS.

1. Construction. The ngnal shon
Rg. 1 70 is provided with two colored le
each S|" in diameter, it may also be ec
ped with three lenses (red, green and yel
when required for three-position work,
case is suspoided from the mast by meai
the bracket shown in the photograph,
attachment between the case and bre
being made by means of a knuckle or
venal joint, so that the signal can be e
focused towards any part of the track:
adiustn>ent is often of great convenii
especially in the case of Hignalling on cu:
The lensea, lamps and teiminal boards
easily be gotten at through the two I
holes whose covers are visible in the side t
the lamp bases are adjustable, so that
lamps can be easily focused with the lei

All small metal parts are sherardized luiu^

the larger parts are well painted to guard against rusting.

2. Range and Application. Under the worst condi-
Umm, with sunlight shining directly on the lenses, the indica-

SIGNALS. 291

tion of this signal is effective up to approximately 2000 feet;
at other times of the day, when the conditions for visibility
are better, the above limit is increased about 50 per cent.
This signal is often used for indications on long l^oclcs on high
speed interurban electric roads.

3. Lenses and Lamps. The lenses of the doublet pat-
tern (a combination of two special lenses), by tAeans of which
a considerable angle of divergence, or spread* of the light rays
is secured; this makes the signal indication more effective on
curves than would be the case with simple lens. Each lens
is illuminated by two 25 watt 1 1 0 volt tungsten lamps con-
nected in multiple.

•■» ■■ w ■*^i

ALTERNATING CURRENT SIGNALINa

SIGNALS. 293

COLOR SIGNALS--OUTDOOR SERVICE.
MODEL 14 LIGHT SIGNALS.

1. Construction. The signal shown in Fig. 171 is built
on the unit basis, each lamp body, complete with its lens and
lamps, being separately mounted on the cast iron front plate,
to which is also attached the sheet iron shield, or background.
The signal may, therefore, be easily equipped with either two
or three lens units to fit it for two-position or three-position
work; in the two-position signal, red and green lenses are em-
ployed to give the usual stop and proceed indications, and to
these a distinctive deep yellow or amber lens is added when a
t'nree-position signal is required. For a three-position signal
the lenses may be arranged either vertically, as in Fig. 172a,
or they may be placed in triangular fashion as illustrated in
Fig. 1 72b. since but one lens is illuminated at a time. The
lamps, lenses and terminal boards are easily gotten at by re-
moving the sheet steel cover plate whose hand grips are shown
at the right of the side view.

2. Range and Application. Under the very worst con-
ditions, with the sunlight shining directly on the lenses, the
indication is effective on a tangent up to approximately 2500
feet: at other times of the day, when the conditions for visi-
bility are better, the above limit is increased by about 30 per
cent. This signal has, therefore, a longer range than any of
the other light signals previously described, and is. therefore,
well fitted for use either on high speed electric or steam roads,
and it has already been successfully applied to this latter ex-
acting service.

3. Lenses and Lamps. The lenses of the model 14 light
signal are 10^" in diameter. They are specially designed for
high efficiency long range work. Where curves are to be sig-
naled, a deflecting prism screen is provided, which, acting in
conjunction with the main lens, serves to deflect or spread the
light rays around the curve; on tangent track, this prismatic
screen is, of course, not required.

When marker lights are not used, two lamps are provided
back of each lens, the filament of one being located directly at
the focal point, and the other being suspended from the top
of the lamp body so that the center of its filament is some-

n* ALTERNATING CURRENT SIGNALING.

what above the optical aius of the lens and between the lens
and its focus. This latter lamp is often celled a "pilot" lamp;
due to the location of its filament above the optical axis of the
lens, its rays are projected diBgonally downward toward the
track, and this insures a distinct short range indication, useful
in intetlockinE limits where marker lights are not generally
used. In order to increase the efiiciency of the lens and lamp
(Nimbination. the filament of the lamp is concentrated in the
formofa small belix. so that, when the filament is placed exact'
ly at the focusof the lens, asin the case of the lower or main

■'«5ir

lamp, practically all the rays are projected directly through the
focus. This concentration results in a strong beam of light,
visible at a great distance. For the sake of uniformity, the main
and pilot lamps are made alike. These lamps have tungsten
filaments, and each lamp takes 20 watts at &volts. In order
to increase their life, the lamps are generally burned at 5^
volts, it being a well known fact that the life of a lamp can be
greatly extended by burning it below normal volt^e.
1 When marker lights are used, as is nowadays frequently the
se in automatic block work, it is customary to use but me

SIGNALS.

lamp equipped with a reflector back of each main signal lens,
as it is not difficult to predict quite accurately the life of the
lamp so that it may be removed before it bums out; if it bums
out prematurely the marker light indicates the presence of a
signal and in the absence of the signal indication the engine-
man must stop. Such a marker light (see Fig. 156) is attach-
ed to the mast a short distance below the signal and is equipped
with one 8 c. p. lamp burning constantly.

FRONT VIEW

Fig. 172b. Three-Position Model 14 Ught Signal With

Placed Triangularly.

CURRENT SICNAUNG.

Fi(, 173. Beun Ufbl Signali in Servies n

POSITION OR BEAM.
LIGHT SIGNAL.

1. Genaral D«*criptian. The beam or position light
dgnal is the joint invention of Mr. A. H. Rudd, Signal Elngi-
neer of the PennQ'lvania Railroad did Dr. William Church-
ill of the Coming Glass Works. 1 1 consists of a number of
light units, or lamp bodies. Fig. 1 74, Bsiembled on a pipe frame
work in vanous combinations, aa aho^^ in A, B and D, of Fig.
175. In all arrangements, the same tight unit is used, this
being usually called the "lamp." and the lamps are spaced
about 16" center to center. The lamp consists of an alum-
inum casting provided with a universal joint for damping it
to the pipe frame work, shown in Fig. 1 74.

All lamp*
are the same \
color. Signal

given by pou'
thmoidy. The
arms support-
ing the lamps

but the proper
lamps for any i
selected through

as the lamps on an electnc sign are

sdected through the circuit controller. Referring to Fig.
1 75, combination A represents a three-position signal.
When the four Lghts in the horisontal row are illuminated,
the signal indicates slop; similarly, a 45 degree aspect means
caution, and a vertical row of lights means proceed, just as in
the case of a right hand upper quadrant semaphore. The
central light bums continuously, as it is common to every in-
dication. Combination B represents a two-position 0-90 signal;
D represents a two-position 0-45 degree signal. In Fig. 176
will be found the complete code of indications, or aspects,
the usual semaphore indications being given in the left band
column and the corresponding position light signal aspects
in the next column to the right, the meaning of the various as-
pects, as translated by the ^gi">""", bong given in th«

298 ALTERNATING CURRENT SIGNALINC.

Mdunm at the extreme right. The three bottom aspects are
those used in autotnatic block work, the others above being
provided for use in interlocking limits; it will be observed
that they are all arranged on the basis of the well known
"speed signaling" scheme. Of course, for an ordinary three-
position signal, the simple three-beam combination shown at
A, Fig. 175, would alone be required.

2. Lenses and Lamps. A 5^" inverted tone lens 2, Fig.

174. is equipped with a "no glare" cover glass; this glass has
a yellowish tinge which renders the light more distinct and '
less liable to be confused with reflections from surrounding
objects. At the focus of the lens is placed a 12-volt 5-watt
concentrated filament tungsten lamp, the filament being about
yi" long and disposed horizontally and at right angles to the
optical axis. A hood 8. Fig 174. is provided to shield the lens

Fig. 175. A Few

from the direct rays of the sun. In order to secure a good
short range indication, a glass mirror reflector 3. Fig. 174. is
mounted above the lamp in such a position as to cast light
downward toward the base of the signal. This effect is fur-
ther aided by the so-called "toric" lens.

3> Range, Although the beam candle-power of the posi-
tion light signal lamp is much less than that of the Model 14
light signal previously described, the transmission factor ot
the lenses is greater, due to the absence of color, so that the
range of the position signal lamp is practically equal to that
of the Model 14 light signal: i. e., 2500 to 4000 feet, depending
upon the sunlight and weather conditions.

SIGNALS,

299

SCMAPMOtC

ASPECTS
LIsMfl

MCAMINO

a=3

3=3

113

I
i

%^w

PROCCCI
PREPIItnTOtTtP

ATNCITSICSIL

PROCCCI

f RCPARCI Tt PAtI HCXT IICNAL

ATyeoiuMtPCCft

fftOCCCO

PRocecoAT ycowM ircco

fRCPARCOTOITOf
ATNCXTflCIIAL

ftOCCCBATMCOIUMSfCCO

PROCCCBATLOWtfCCO

PRCPARCOTOITOP

TRACK MAT oeacconci Oft

NCXTSICNALATITOP

fROCCCOATLOWSfCeO

STOP
TNCMPR0CeC0-l(ULCS04

PROCCCO
PRCPARCDTOSTOP

AritCITSICNAL

PROCCCO

PRCPARCO TO PISt MXT tURAL

ATMCOIUMIPCCO

PROCCn

Fig. 1 76. Beam Light Signal Aspecta and Tlteir Meaning.

COLOR LIGHT SIGNALS
FOR SUBWAY AND TUNNEL WORK.

1. Description. In general, color signals for use in sub-
much candle-power back of their lenses, fts similar signals for
service out of doors, for the obvious reason that sunUgbt does
not have to be contended with. On account of this, light
signals for underground work are very simple in construction.
This will be evident from an inspection of Fig. 1 77, illustrat-
ing the home and distant signals used in the Hudson and
Manhattan tunnels in New York. Here the signals are of the

placed one
above the
other, «s
shown at tha
right of the
photograph;
each circular

is divided ver-
tically into two
light proof

Fig. 177. Lifht S>En>K Hu<l»n and Miiihiittu ments. each

provided with

a simple optical lens. The top, or home, signal, is provided

with red and green lenses, and the bottom or distant, signal

with red and yellow lenses.

Another form of tunnel signal ia illustrated in Fig. 178. this
being a drawing of one of the light signals recently installed
in the Boylston Street Subway of the Boston Elevated Rail-
road; the signal ia of the three-position type, having three
lenses, red, yellow and green, housed in a simple sheet iron
case, each lens being illuminated by two 4 C. P. 55 volt tung-
sten lamps. The track aide of the signal i« provided with
hinged sheet iron doors, which allow easy access to the lamps,
lenses, etc. The signal shows up very brightly in the dark
tunnel, and, as in the case of tha ainukr aignal ahewn in Fig.

1 77, the indication is visible over much Br«*t«r distance than
the pennissible block length as dictated by traffic cooditiona
Fig. 179 il-

greatcr candle
piower.Bnd also
with hoods to
shield them

from sunlight, nmwo' nanimm

as illustrated FLg. 178. Thr« Li,lit T»n«l SigwU

in the photo-
graph. The interlocking signals are provided with five lenaoi,
the three upper ones fulfilling the function of a three-poM-
tion high speed aignal, and the two lower ones that of a two*
position low speed route or "calling on" signaL

ALTERNATING CURREhTT SIGNALING.

Fi(. 179. Liibt Sisnali in iha PennylvuiU Tumul An*

CHAPTER IX.

TRANSMISSION SYSTEMS

AND

POWER HOUSE EQUIPMENV.

CHAPTER IX.

TRANSMISSION SYSTEMS
AND POWER HOUSE EQUIPMENT.

General Considerations. One of the most attractive fea-
tures of the alternating current system of signaling is the
practicability of transmitting power economically over long
distances from one central power house. This is in line with
the modem Central Station idea — the unified supply of power
for a district from one central station where power can be
generated economically and efficiendy by large units. Of
course an A. C. transmission along the right of way need not
be restricted to supplying power to signals. It may be, and
in many cases is, employed as a j<Mnt power supply for sig-
nals, station lighting, mercury arc rectifiers, motor driven
pumps, and a score of other utilities which soon appear once
cheap power is available. The generating-transmission sys-
tem has therefore contributed important conunercial advan-
tages— economy and utility — to alternating current sig-
naling.

Ultimately, the success of any signaling system depends
primarily upon its reliability, and in the A. C. system the
power supply is an important link in the chain, for on its in-
tegrity depends the continuity of service without which the
most perfect signals and relays are useless. In the power
house, this involves either a dependable commercial power
supply, in addition to the main generating equipment, or dse
duplicate apparatus. The transmission line, if aerial, must
be strong enough to withstand, with a good margin of safety,
all sleet and wind strains to which it is liable to be subjected,
and, if underground, the wires must be well insulated and
<:arefully laid to guard against the necessity of ripping the
line up in case defects develop after installation. Care in de-
sign and construction of the generating apparatus and trans-
mission will avoid traffic delays due to interruptions in the
power supply.

Next comes the question of first cost and operating econ-
omy. Obviously, through the use of a heavy copper trans-
mission, the power losses may be reduced to any desired quan-
ti^. but a point is finally reached where the interest on the

306 ALTERNATING CURRENT SIGNALING.

money invested in extra copper exceeds the money saved in
power losses through the use of that extra copper. The sub'
ject resolves itself into a judicious balancing of first cost
against losses. So many local conditions demand special
consideration that each case must be treated on its own
merits. In such matters there is plenty of room for individ-
ual skill and good judgment.

In order to secure reliability and high operating economy
with a moderate first cost, the power transmission system
must, therefore, be thoroughly studied, and in this connec-
tion, the signalman will do well to be very careful in adopting
any formula or rules given in the standard text-books on high
tension transmission, for while the same fundamental prin-
ciples underlie the design of all transmissions, the problem of
carrying, say, 50 K. V. A. over 25 miles for a signal system
is radically different from that of transmitting 20,000 K. V. A.
for the supply of a city 100 miles away. It is, therefore, the
object of this chapter to discuss the more important technical
and practical considerations governing the design of trans-
mission systems and power equipment adapted to meet the
rather peculiar requirements characterizing alternating cur-
rent signal systems.

THE TRANSMISSION.
Voltage and Line Wire Size.

1. Voltage. Given a transmission of stated length and
the amount of power to be delivered, the first question which
arises is that of the voltage at which power is to be transniit-
ted; we will first determine what part the voltage plays in the
calculations.

If the line and load are operating on imity power factor
(current and voltage in phase) the power delivered to the line
may be expressed in watts as W = IE, where E is the initial
voltage impressed on the transmission and I the current. In
most cases, however, the current and voltage will be consid-
erably out of phase on account of the fact that the track cir-
cuit apparatus and the induction motors operating the signals
are of a highly inductive character; the power factor of the
load at the power house will, therefore, in the case of most
signal systems, be in the neighborhcxxl of 0.6 to 0.7. in whicb

TRANSMISSION SYSTEMS.

307

case the power delivered to the Hne will be expressed as W =
I E cos 0 » where cos 6 is the power factor* or in other
words, the cosine of the lag angle between the current I and
the voltage E.

A given amount of power W can therefore be delivered to
the line either at low voltage and a correspondingly higher
current, or at high voltage and a small current, the product
of current and voltage (volt-amperes) being the same in
either case. It becomes immediately evident that the em-
ployment of a high voltage is desirable, as only a small cur-
rent need be carried by the transmission, for then small line
wires may be employed, involving only a relatively small in-
vestment in copper. High transmission voltage is therefore
the secret of low first cost of the transmission line.

Let us see what this means. Take, for example, the prob-
lem of delivering at the end of a 30 mile single-phase line 30
kilo-watts net power at unity power factor after a 1 0 per
cent loss in transmission. At the power house 53 K. W.
must be fed into the line, the loss, of course, being 3
K. W. Table I below illustrates the enormous saving in
money ejected through the use of high transmission volt-
ages, the first column indicating the trial voltages em-
ployed, the second column the corresponding currents,
and the third, fourth and fifth columns, the size, weight and
cost of copper for each case, the cost of the copper being
taken at 16c per pound. In calculating the table, the various

TABLE L

Showing the decreasing cost of copper with increasing line
voltages for a 30 mile single-phase transmission delivering
30 K. W. after 1 0 per cent line loss, neglecting inductance
and skin effect.

Voltage

Current

Copper.

Diam. Line
Wire

Total
Weight

Cost

220 volts
1100 "
2200 "
4400 '*

11000 ••

250 amps.

60 '^

26 ••

12.6 ••

6 '*

6 . 55 in.
1.31

0.655 ••
0.3275 ••
0.131 '•

20,300 tons

812 "

203 "

50.75 "

8.12 ••

$6,500,000

260,000

65,000

16,250

2,600

308 ALTERNATING CURRENT SIGNALING.

-~ ' I I I I L

currents were found, of course, by dividing the initial power,
55 kilowatts (55000 watts), by the corresponding voltages,
after which the resistcoice R of the line may be solved for. the
10 per cent, loss (5000 watts, constant in each case) being
simply P R of which R is the only unknown, quantity, R
once determined for the given length of wire (60 miles for the
two wires of a single phase transmission), the size and weight of
the corresponding copper can be looked up in the wire tables
at the back of this book.

Tlie following simple rules, illustrated by the above table*
are easily memorized and will often prove handy.

1. The energy loss varies with the square of the current.
Halving the current divides the absolute loss by four, and the
percentage loss by two, since the total power is proportional
to the current, the e.m.f. being fixed.

2. With a fixed percentage loss, doubling the working
voltage will divide the amount of copper required by four,
since the current for e given amount of power will be reduced
by one-half, while the actual volts lost will be doubled in
maintaining HiO fixed percentage.

3. The amount of copper required for transmitting a given
amount of pov:er a given distcoice, at a fixed efficiency, will
vary inversely as the square of the voltage.

4. If the length of the transmission is doubled, the area
of the conductor must be doubled also; consequently, since
the length is doubled, the weight of copper will be increased
four times. Hence, for the same energy transmitted at the
same per cent, efficiency, and the same voltage, the total
weight of copper will be increased directly as the square of
the distance. By increasing the voltage in direct proportion
to the distance, the weight of copper required for a given per-
centage loss will be made a constant quantity independent 0£
the distance.

2. Choice of Voltage. Generally speaking, therefore, tho
higher the pressure the less the transmission will cost with a
given line loss. In view of the economy in copper secured
through the employment of high transmission voltages, the
question immediately arises as to what is the limit in voltage.
The answer lies in the fact that the higher one goes in voltage
the greatar bacomai tha ganaral strain en tha insulation o£

TRANSMISSION SYSTEMS. 309

the line and the apparatus connected to it; in other words,
as the voltage mounts, it becomes more difficult and expensive
to insulate the transformers, and at the same time the other
line auxiliaries — ^insulators, lighting arresters, fuse cutouts,
etc., become more costly.

Given, then, the length of the line and the power to be
transmitted, what voltage and what line wire size will give
us the most economical arrangement with a reasonably loss in
the transmission While, on account of the variable jfactors
entering into the calculation, no general rule or formula can
be laid down, the process of selection is considerably simpli-
fied on account of certain limits within which it is advisable
to work. Tliese limits are as follows:

1. ' The commercial voltages for which transform<s^ and
other transmission apparatus are generally built are ^200,
3300, 4400, 6600 and 1 1,000; it is not advisable to select a
mongrel voltage. Voltages of under 2200 are rarely used in
signal work as most commercial transformers, lightning ar-
resters, transformer fuse cutouts, etc., are built to stand at
least that voltage, and nothing will be gained as far as they are
concerned in going to 1 1 00 volts or lower, while for given line
loss the line wire size would have to be greater. On the other
hand, before going above 2200 volts with given line loss, the
saving in copper thus effected must more than compensate
for the additional cost of the transformers and line auxiliaries.

2. Tlie allowable percentage loss on the line must next be
decided on, for the efficiency of the transmission may be made
as high as you please, depending on how much money you are
willing to invest in copper. In signal work it is customary to
allow a 10 per cent, voltage loss in the line with all signals
clear.

Per cent, voltage loss =— ^t — ^

where Eq = volts at generator end and Ej = volts at load end.
After the voltage and line wire size have been determined
on, the voltage drop with all signals clearing at once (as occurs
after an interruption in the power supply) should be calcu-
lated; if the line drop is excessive the signals at the end of the
transmission farthest away from the power house may not re-
ceive sufficient voltage to clear them. Depending on the
type of •igna' used and th« rtlative power taken by the track

310 ALTERNATING CURRENT SIGNALING.

circuits, which is of course constant, the percentage voltage
loss with all signals clearing will run from 15 per cent, to 20
per cent. If the line wire size calculated to give a 10 per cent,
loss with all signals clear is found to give too low a voltage
at the far end of the line with all signals clearing simultaneous-
ly, then a larger conductor must be employed. The signal
manufacturer will furnish data covering the normal and mini-
mum voltages on which his signals will work and the differ-
ence between the two will, of course, indicate the permissible
variation in voltage loss; data of this character is given in
Chapter VI II.

3. The line wire must be of a commercial gauge; for ex-
ample, the calculations will generally indicate a conductor
falling midway between two standard sizes; it would not pay
to have a special wire drawn, and therefore the nearest larger
size conductor as given in the wire table should be employed. '

4. Regardless of electrical calculations, the wire must be
strong enough mechanically to bear up not only under its
own weight, but also under any additional wind or sleet load
to which it may be subjected. Under no circumstances
should the wires of an aerial transmission be smaller than No.
1 0 B. & S. solid copper or No. 1 2 B. & S. copper clad.

The selection of voltage and line wire size for a transmission
system of minimum first cost and proper line loss character-
istics resolves itself into a cut and try process; but, keeping the
above limitations in mind, the designer cannot go very far
astray. He should start out with a trial voltage of 2200 and
then compute the total cost of the corresponding line with its
transformers and other auxiliaries. The next calculation,
made on the basis of 3300 volts, will indicate whether money
can be saved through the employment of a higher voltage*
and this process should be continued until the most econom-
ical combination of line wire size and voltage is discovered*
all the calculations, of course, being based on the same per-
centage voltage loss.

3. Voltages and Line Wire Sizes Frequently Used in
Signal Work. Naturally, the voltage and line wire size for
any given system will depend entirely upon the extent of the
system, but, in the case of many signal systems, 2200 volts
vdll be found satisfactory, and in order to avoid the extra cost

TRANSMISSION SYSTEMS. 3 1 1

for lightning arresters, fuse cut-outs and transformers, 2200
volt transmissions have become common for lines of a mod-
erate length of, say, 23 miles. On this basis, a stretch of
signaling twice as long would double the transmission load,
and with the same size line wire as for 2200 volts, a 4400 volt
transmission would give the same percentage line drop over
fifty miles. The author has in mind a tjrpical stretch of fifty
miles of double track on a steam road, where a 4400 volt, 60
cycle, single phase transmission, with No. 4 copper gave
the very moderate drop of 8 per cent, with all signals clear,
and 15 per cent, with all clearing at once, the transmission,
in addition, carrying a station lighting load. In another case,
one involving the transmission of signal and station lighting
load for a 1 50 mile stretch of double track steam road, trial
calculations showed that a single phase transmission at 1 1 000
volts with No. 6 copper clad wires would be the most eco-
nomical. No general rule for such calculations can be laid
down, however. ELach case must be considered on its indi-
vidual merits.

CHOICE OF FREQUENCY.

4. Twenty^Five vs. Sixty Cycles. Coming now to the
matter of frequency, we may choose either of the commercial
frequencies, 25 or 60 cycles. From the viewpoint of power
economy, 25 cycles has somewhat of an advantage, because,
in the first place, the reactance drop in the transmission is
less on 25 cycles than on 60, as will prcisently be explained.
In addition to this, a 25 cycle track circuit of given length
will require less power than one operating on 60 cycles, be-
cause the drop in the rails, and, consequently, the volts at
the track transformer, are less with the lower frequency. Tlie
same statements apply also to the power for the signals.

Aside from such technical considerations, however, other
practical considerations must be taken into account. In all
cases, it is advisable to have an auxiliary power supply to
fall back on, if the power house fails, and almost invariably
the frequency of the commercial sources of power available
in towns along the right-of-way will be found to be 60 cycles,
as 25 cycles is not satisfactory for lighting purposes, on ac-
count of the "flicker" of the lamps due to the low frequency.

312 ALTERNATING CURRENT SIGNALING.

— n — n ■

This fact is of great importcoice in choosing the frequency of
a signal system for steam roads; in the case of dectric roads,
of course, it is not of much importance, for, if the A. C. power
fails, then the rotaries are tied up and cars cannot run any*
way. It must be kept in mind, in making up cost estimates,
that 23 cycle transformers and power apparatus cost more
than 60 cycle apparatus, which, of course, is an item in favor
of a 60 cycle system.

In settling the matter of frequency, therefore, the
amounts of power required on 23 and 60 cycles, auxiliary
commercial supply, and relative cost of apparatus, must
be considered. Elxcept in rare instcoices, the ditference
between the amounts of power at 23 or 60 cycles will
not be of great consequence; the author has in mind a
typical case on a steam road where the power for a double
signal location with two one-mile track circuits, totalled 330
V. A., 162 watts on 23 cycles, as against 407 V. A., 159 watts
on 60 cycles, although with other types of apparatus, and
other conditions, the ditference might well have been much
greater, and thus have made the case for 23 cycles stronger.
The reader is referred to an excellent article on this subject,
written by Mr. J. E. Saunders, and published in the 1913
Proceedings of the R. S. A., covering the selection of fre-
quency under a particular set of conditions.

PRACTICAL CALCULATIONS.

5. Resistance^ Reactance and Impedance DrofM.

Tlius far in the discussion, for the sake of simplicity, the drop
in the line has been calculated as a purely resistance drop —
I R — but, actually, due to the inductive effect of thd current
flowing in the wire, there is a reactiee drop, the square root of
the sum of the squares of the two (or what is the same thing,
the product of the current into the total impedance of the
line), constituting the impedance drop. The numerical dif-
ference between the initial impressed voltage and the receiver
voltage at the end of the line is called simply the line drop.
The impedance drop is not the same as the line drop, as will
presendy be shown.

As is well known, when a current traverses a coil of wire
^fnes of magnetic force spring out from the coils, and in doing

TRANSMISSION SYSTEMS. 313

*— — I ■ III — I.. I ■»

SO, cut the coils and induce a voltage theron in opposition to
the impressed voltage. Now» self-induction will result even
if the wire is not coiled, for, as the lines of force spring cir-
cularly outward from the theoretical center of the wire, just
as happens when a stone is thrown into a pond, the body of
the wire is itself cut by the expanding circular lines of force,
and a counter voltage is induced in the wire, thus increasing
the apparent drop. This is just what happens in the case of
transmission wires, the inductive etfect being more marked,
of course, as the diameter of the wire increases. The spacing
of the wires has, however, an important bearing on the self-
induction of the transmission, for, taking, as an example, the
two paralld wires of a single-phase line, the currents in the
wires are flowing in opposite directions, going and coming;
due to this fact, the circular expanding lines of magnetic
force are of opposite direction, according to the Corkscrew
Rule, stating that, if the inward motion of the corkscrew rep-
resents the direction of the current in the wire, then the di-
rection of its circular motion represents the direction in which
the magnetic lines of force are traveling, and, if the two wires
are very close to each other, the magnetic fields will almost
neutralize each other, and the reactive effect will practically
disappear. As the wires are spread farther and farther apart,
the magnetic fields of the two wires become separated, and
some of the lines linked with one wire do not cut the other,
in which case the neutralizing effect above described becomes
of less and less consequence, with the result that, finally, the
self-induction of each wire has to be reckoned with. The
coefficient of self-induction in millihenrys for one conductor
of an overhead transmission line one mile long is given by the
formula:

Millihenrys = 0.741 x logi o (2.568 -j) (I)

Where D is the distance between centers of the outward and
return conductors and d is the diameter of one conductor,
these measurements being expressed in inches. This formula
applies to a conductor of any non-magnetic material, such as
copper or aluminum but not to steel wires or wires with a
steel core.

Table II calculated from the above formula gives at vari-
ous spadngs the self-inductance of solid non-magnetic wires

314

ALTERNATING CURRENT SIGNALINa

TABLE IL

SELF INDUCTANCE OF SOLID NON-MaCNETIC WIRES*

Millilienries per MILE oi each wire of a single-phase or of a symmetrical

three-phase line

Size of

wire,

cir. mils.

or A.W.G.

Diam.

of wire,

inches

Inches between wires, center to center

• 30

X, 000,000

X 0000

0.3036

0.6572

0.8803

I. oil

1.103

1.234

1.327

1.398

750.000

0.8660

0.3499

0.703s

0.9266

1.057

1. 150

1.280

1.373

1.445

500,000

0,7071

0.4152

0.7688

0.9919

1. 122

X.215

1.346

1.438

1. 510

350.000

0.5916

0.4726

0.8262

1.049

1. 180

1.272

1.403

1.496

1.567

350,000

0.5000

0.5267

0.8803

1. 103

1.234

X.327

1.4S7

1.550

1.622

0000

0.4600

0.5536

0.9072

1. 130

X.261

1.353

1.484

1.577

X.648

000

0.4096

0.5909

0.9445

1. 168

X.298

X.391

1.521

1. 614

1.686

0.3648

0.6282

0.9818

1. 205

1.315

X.428

1.559

1.651

1.723

0.3249

0.6654

X.019

1.242

1.373

1.465

1.596

1.688

1.760

0.2893

0.7029

1.057

1.280

1. 410

1.503

1.633

1.726

1.798

0.2576

0.7402

I 094

1. 317

1.447

1.540

1. 671

1.763

1.835

0.2043

0.8148

1. 168

1.392

1.522

1. 615

1.745

1.838

X.910

0.1620

0.8894

1.243

,1.466

1.597

1.689

1.820

X.912

1.984

0.1285

0.9641

1. 318

I 541

1. 671

1.764

1.894

1.987

2.059

0. 1019

1.039

1.392

1.615

1.746

1.839

1.969

2.062

2.134

0.08086

1. 113

1.467

1.690

1. 821

1. 913

2.044

2.136

2.208

0.06408

1. 188

1.542

1.76s

1.895

1.988

2. 118

2. 211

2.283

0.05082

1.263

1. 616

1.839

1.970

2.062

2.193

2.286

2.357

Size of

wire,

cir. mils.

]

Feet between ¥

rires, cc

snter to

center

or A.W.G.

1 .000,000

1. 457

1. 550

1.622

1.680

1.773

1.84s

1.975

2.068

2.X40

7SO.OOO

1.503

1.596

1.668

1.726

1. 819

X.891

2.021

2. 114

2.186

500.000

1.569

X.66X

1.733

1.792

1.884

1.956

2.087

2.179

2.251

3SO.00O

1,626

1. 719

1.791

1.849

1.942

2.014

2.144

2.237

2.309

250.000

1.680

1-773

1.845

1.903

1.996

2.06R

2.198

2.291

2.363

0000

1.707

1.800

1.872

1.930

2.023

2.095

2.225

2.3x8

2.390

000

1.744

1.837

1.909

1.967

2.060

2.132

2.262

2.355

2.427

X.782

1.874

1.946

2.005

2.097

2.169

2.300

2.392

2.464

1. 819

1. 911

1.983

2.042

2.135

2.306

2.337

2.430

2.501

X.856

1.949

2.021

2.079

2.172

2.244

2.374

2.467

2.539

1.894

1.986

2.058

2. 117

2.209

2.2S1

2.412

2.504

2.576

1.968

2.061

2.133

2. 191

2.384

2.356

2.486

2.579

2.651

2.043

2.135

2.207-

2.266

2.359

2.430

2.561

2.654

2.72s

2. 118

2.210

2.282

2.341

2.433

2.505

2.636

2.728

2.800

3.193

2.285

2.357

2.415

2.508

2.580

2.710

2.803

2.875

2.267

2.359

2.431

2.490

2.582

2.654

2.785

2.«77

2.949

2.341

2.434

2.506

2.56s

2.657

2.729

2.860

2.952

3024

2.416 2.509

2.581 2.639

2.732

2.804

2.934 3.027 3.099

* The inductances given in this table
oidinaiy stxaadod wires oi the same cross-

also apply, with a practically negligible error, to
secthn.

TRANSMISSION SYSTEMS.

315

TABLE III.

2S-CYCLE REACTANCE OF SOLID NON-MAGNETIC WIRES'

Ohms per MILE of each wire of a single^phas^ or of a symmetrical

three-phase line

Size of

wire,

cir. mUs.

or A.W,G.

Diam.

of wire,

inches

Inches between wires, center to center

1,000,000

750,000

$00,000

x.oooo
0.8660
0.7071

0.04770
0.05497
0.06523

0.1032
o.iios
0.1208

0.1383

0.1456
0.1558

0 1588
0.1661
0.1763

0.1733
0.1807
0.1909

0.1939
0.2011
0.2115

0.2085

0.2157
0.3259

0.2196
0.2270
0.3372

350.000
250.000

0.5916
0.5000
0.4600

0.0742s
0.08274
0.08697

0.1298
0.1383
0.1425

0.1648
0.1733
0.1775

0.1854
0. 1939
0.1981

0.1998
0.2085
0.2126

0.3204
0.2289
0.2331

0.2350
0.2435
0.2477

0.3462
0.2548
0.2589

000

0.4096
0.3648

0.3249

0.09283
0.09869
0.104s

0. 1484
0. 1542
0.1601

0.183s
0.1893
0.I9SI

0.2039
0.2097
0.2157

0.2185
0.2243
0.2302

0.2389

0.2449
0.2507

0.2536

0.2594
0.2652

0.2649
0.2707
0.3765

I
3
4

0.3893
0.3576

0.3043

O.IIOI

O.I 163
0.1280

0.1661
0.1719
0.183s

0.30II

0.2069
0.2187

0.3215
0.2273
0.2391

0.2361
0.2419
0.2537

0.2565
0.262s

0.2741

0.2712
0.2770
0.2887

0.3835
0.3883
0.3001

0.1630
0.1285
O.IOI9

0.1397
0.151s
0.1632

0.1953
0.2071

0.2187

0.2303
0.2421
0.2537

0.2509
0.2625
0.2743

0.2653
0.2771
0.2889

0.2859
0.2975
0.3093

0.3004
0.3122

0.3239

0.3117
0.323s
0.3353

14
16

0.08081
0.06406
0.05082

0.1749
0.1866

O.I9R4

0.2305
0. 2422

0.2539

0.2655
0.2773
0.2889

0.2861
0.2977
0.3095

0.300s
0.3123
0.3239

O.3211
0.3327
0.3445

o.3\s6
0.3473
0.3591

0.3469
0.3587
0.3703

Size of

wire,
cir. mils,
or A.W.G.

Feet be

tweeni

Rrires, c

enter to

center

XS^

»s

1,000,000

750,000
500000

0.3389
0.3361
0.346s

0.3435
0.2507
0.2609

0.2548
0.2620
0.3723

0.3639
0.2712
0.2815

0.2785
0.2858
0.2960

0.2898
o.297r
0.3073

0.3103
0.317s
0.3279

0.3249
0.3321
0.3423

0.3362
0.3434
0.3536

, 350.000
350,000

0.3554
0.2639
0.3682

0.2701
0.2785
0.3828

0.2814
0.2898
0.2941

0.3905
0.2990
0.3032

0.3051
0.3136
0.3178

0.3164
0.3249
0.3291

0.3368

0.3453

0.3495

0.3514

0.3599
0.3642

0.3627
0.3712

0.3755

000

00
0

0.3740
0.3800
0.2858

0.2886

0.2944
0.3002

0.2999
0.3057
0.311S

0.3090
0.31S0
0.3208

0.3236
0.3294
0.3354

0.3349
0.3407
0.3466

0.3554
0.3613
0.3671

0.3700
0.3758
0.3818

0.3813
0.3871
0.3929

3
4

0.2916

0.3975
0.3092

0.3062

0.3X30
0.3238

0.3175
0.3233
0.33SI

0.3266
0.3326
0.3442

0.3412
0.3470
0.3S88

0.3525
0.3583
0.3701

0.3730
0.3789
0.3906

0.3876

0.3934
0.4052

0.3989
0.4047
0.416s

8
10

0.3210
0.3327
0.3444

0.3354

0.3472
0.3590

0.3467
0.3585
0.3703

03560
0.3678
0.3794

0.3706
0.3822
0.3940

0.3818
0.3935
0.4053

04023

0.4141
0.4257

0.4169
0.4286
0.4404

0.4281
0.4399
0.4517

14
16

0.3561

0.3678
0.3796

0.3706
0.3824
0.3942

0.3819
0.3937
0.40SS

0.3912
0.4030
0.4146

0.4056

0.4174
0.4292

0.4169
0.4287
0.4405

0.4375
0.4493
0.4609

0.4520
0.4638
0.4755

0.4633
0.47SI
0.4869

* The reactances given in this table also apply, with a practically negligible error, to
Mdiaary stranded wires of the same cross-section.

S16

ALTERNATING CURRENT SIGNALING.

TABLE IV.

60-CYCLE REACTANCE OP SOLID NON-MAGNETIC WIRES'

Oluns per MILE of each wire of a single-phase or of a symmetrical

three-phase line

Size of

wire,
cir. mils,
or A.W.G.

Diam.

of wire,

ioches

Inches between wires, center to center

1,000.000
750.000
500.000

I. 0000

0.8660
0.7071

0.1145
0.1319
0.156s

0.2478
0.2652
0.2898

0.3319
0.3493
0.3739

0.3811
0.3985
0.4230

0.415S
0.4336
0.4581

0.4C52
0 48.^6
0.5074

05003
0.5176
0.5421

O.S270
0.5448
0.5693

3SO.O0O

250.000

0000

0.5916
0.5000
0.4600

0.1782
0.1986
0.2087

0.311S

0.3319
0.34JO

0.3955
0.4158
0.42G0

0.4449
0.4652
0.4754

0.4795
0.5003
0.5101

0.5289
0.5493
0.5595

0.5640
0.5844
0.594S

0.5908
0.6115
0.6213

000

0.4096
0.3648
0.3249

0.2228
0.2368
0.2509

o.3S6i
0.3701
0.384^

0.4403
0.4543
0.4682

0.4893
0.5033
0.5176

0.5244
0.5384
0.5523

0.5734

0.5877
0.6017

0.608s
0.6224
0 6364

0.6356
0.6496
0.6635

I
2

0.2893
0.2576
0.2043

0.2650

0.2791
.0.3072

0.3985
0.4124
0.4403

0.4826
0.4965
0.5248

0.5316
0.5453
0.5738

0.5666
0.5806
0.6089

0.6156
0.6300

0.6579

0.6507
0.6647
0.6929

0.6778
0.6918
0.7201

0.1620
0.1285
0.1019

o.XVii
0.3635
0.3917

0.4686

.0.4969
0.5248

0.5527
0.5810
0.6089

0.6021
0.6300
0.6582

0.6368
0.6650
0.6933

0.6861
0.7140
0.7423

0.7208

o.749»
0.7774

0.7480
0.776^2
0.8045

14
16

0.08081
0.06408
0.05082

0.4196

0.4479
0.4762

0.5531
0.5813
0.6092

0.6371
0.6654
0.6931

0.6865

o.ri44
0.7427

0 7212

0.749s
0.7774

0.7706

0.7985
0.8268

0.8053
0.83^5
0.8618

0.8324
0.8607

0.8886

Size of

wirfr,

cir. mils.

or A.W.G.

Feet be

tween wires, ceater to center

1^000.000

750,000
500,000

0.5493
0.5666

0.591S

0.5844
0.6017
0.6262

0.6115
0.6288

0.6533

0.6334
0.6507
0.6756

0.6684
0.6858

0.7103

0.6956
0.7129
0.7374

0.7446
0.7619
0.7868

0.7796
0.7970
0.8215

0.806S

0.8241

0.8486

350,000

250.000

0000

0.6130
0.6334
0.643s

0.6481
0.6684
0.6786

0.6752
0.^56
0.7057

0-6971
0.7174
0.7276

0.7321
0.7525
0.7627

0.7593
0.7796
0.7898

0.8083
0.8286
0.8388

0.8433

0.86i7

0.8739

0.870s
08909

0.9010

000

0.657s
0.6718
0.6858

0.692s
0.706s
0.7204

0.7196
0.73.16
0.7476

0.7416
0.75S9
0.7698

0.7766
0.7906
0.8049

0.8038
0.8177
0.8317

0.8528
0.8671
0.8810

0.8878
0.9018
0.9161

0.9150
0 9289

0.9429

I
2
4

0.6997
0.7140
0.7419

0.7348
0.7487
0.7770

0.7619

0.7759
0.8041

0.7838
0.7981
0.8260

0.8188
0.8328
0.8611

0.8460

0.8599
0.8882

0.8950
0.9093
0.9372

0.9J01
0.9440
0.9723

0.9572
0.9712
0.9994

0.7702
0.798s
0.8264

0.8049
0.8332
0.8614

0.8320
0.8603
0.8886

0.8543
0.8826
0.9105

0.8893
0.9172

0.9455

0 9161
0.9444
0.9727

09655
0.9938
1.022

I.OOI

1.028
1.057

1.027
1.056
1.084

14
16

0.8547
0.8826
0.9108

0.8893
0.9176

0.9459

0.9165
0.9448
0.9730

0.9387
0.9670

0.9949

0.9734

1.002

1.030

1. 001
1.029
1.057

X.050
1.078
1. 106

1.065

1. 113

1. 141

1. 112
1.140
1. 168

* The reacLances given ia this Uble also apply, with a praaicaUy negligible error, ta
Tdiiuiy stranded wires of the samt cross-seawtf

TRANSMISSION SYSTEMS.

$\7

in millihenrys per mile of each wire of a single-phase or of a
symmetrical three-phase line; the total self -inductance of the
two conductors of a single-phase line is of course twice that
of a single conductor, and in a three-phase line the total self-
inductance 18 V 3 times as great as that of one of the three
conductors of which it is composed. Table III is the cor-
responding reactance at 25 cycles and is derived from Table
1 1 by the formula X = Lp, where X is the reactance in oh^s,
L is the self -inductance in henrys and p = iTtn, where n is
che frequency in cycles per second. Table IV covers the re-
actance at 60 cycles. Self-inductances and reactances for other
wire spacings and frequencies can be easily calculated from
equation (I ) above and the formula X = Lp. Table V shctws
the resistance, reactance and impedance (2= -y/R^ -{- J^^)
of copper clad wire of 40 per cent, conductivity; the react-
ance and impedance of this latter wire are naturally much
greater than the similar Unctions of non-magnetic wires, such
as copper or aluminum.

TABLE V.

Resistance, Reactance and Impedance

40% Copper Clad Wire.

Ail Values for One Mile Single Wire.

Current 5 Amperes.

Size

Spac-
ing

D.C.Res.
1 Mile

25 Cycles

60 Cycles

A.C.
Res.

Ind.
React.

Imp.

A.C.
Res.

Ind.
React.

Imp.

No. 6
No. 6
No. 6
No. 8
No. 8
No. 8
No. 10
No. 10
No. 10
No. 12
No. 12
No. 12
No. 14
No. 14
No. 14

12"
18"
24"
12"
18"
24"
12"
18"
24"
12"
18"
24"
12"
18"
24"

4.86

9.15

12.03

19.73

29.20

4.92

9.18

12.09

19.73

29.20

.316
.343
.369
.348
.375
.390
.296
.317
.338
.296
.317
.338
.264
.295
.317

4.93

9.19

12.10

19.76

19.75

29.20

4.92

9.18

12.09

12,09

12.09

19.73

29.20

.771
.822
.873
.882
.919
.956
.750
.792
.833
.728
.778
.828
.685
.752
.818

4.98

4.99

5.00

9.23

12.11

19.77

29.20

6. Calculation of Line Drop. Let the line Ol in Fig. ^60
represent the current flowing through the transmission Hoe

318 ALTERNATING CURRENT SIGNALING.

' ■ »

and the receiving circuit; let £^ represent the voltage at the
load at the end of the line and 0. the phase difference between

Fig. 180. Elementary Vector Diagram of Transmission Line.

E I and I , depending on the power factor of the load. I f R is the
total resistance and X the total reactance of the transmission
line, Eq the voltage of the generator, will be the vectorial sum
of the receiver voltage E^ . and the impedance drop ZI. which
latter is of course the vectorial sum of the resistance drop RI
and the reactance drop XI. The resistance drop RI is laid
off parallel to OI, as it is in phase with the current; the re->
actance drop XI is laid off perpendicular to the current vector
OI, as the reactance drop is 90^ out of phase with the cur*
rent. The numerical difference between Eq and E^ is the line
drop, as would be indicated by the difference between simul-
taneous voltmeter readings taken at the generating and re-
ceiving ends of the line. It will be seen, therefore, that the
line drop is not the same as the impedance drop ZI ; the line
drop depends not only on the impedance drop, but also upon
the phase relation between the generator and receiver
voltages.

7. Calculation for Wire Size. Given the line drop
suppose it is desired to determine the wire size for a single-
phase transmission of stated length and wire spacing, to de-
liver a prescribed amount of power P at a prescribed voltage
Ej and frequency to a receiving circuit of power factor cos 9.
As in the previous case, the generator voltage Eq is the numer-
ical sum of the receiver voltage E^ and the line drop. The
power P to be delivered is P watts = Ej I cos 9 , from which
the load current I can be determined, E^ and cos 9 being
stated. Referring now to Fig. 181, which covers the prob-
lem vectorially, the component of E]^ in phase with the cur-

TRANSMISSION SYSTEMS.

319

rent I is E^ cos 6. and the corresponding reactance com-
ponent is E»i sin 0 at right angles to. the current.. By

^E|SINe

E| COS e

Fig. 181. Initial Voltage Impresaed on Transmission Line Divided Into Its

Components.

treating the problem first as a direct current proposi-
tion» an approximate resistance R^ of the line is found
from the relation IR^ = line drop. From this trial
resistance and the known length of line, the approximate
size of the wire may be found from the wire tables in the
back of the book; the wire size thus determined may with
ample accuracy be used to find the corresponding line react-
ance, at the given frequency, from Tables III, IV, or V, for
even if the calculations finally show that the reactance drop
is such as to require the next larger size of wire, the difference
in reactance will be negligible.

The component of Eq parallel to I is (E^ cos 9 + RI ) where
R is the true resistance of the line to be solved for, and the
component of Eq perpendicular to I is (E^^ sin 0 -}- XI).
The diagram shows that:

Eo^ = (El cos e + RI)2 + (El sin 9 + XI)2 (2)

and RI = VEq^ —(El sin 9 + XI)^ — Ei cos. 9 (3)

j^ ^ VEq^ —(El sin e + XI)^ —El COS. 9 (4)

and from this latter equation (4), the true line resistance R
may be found, and, in turn, the corresponding size of wire
from the wire tables as previously described.

8. Example of Signal Transmission Calculation. Let
us take as a concrete case the design of a transmission for a
short stretch of single track electric interurban road 1 5 miles

320

ALTERNATING CURRENT SIGNALING.

long, the power at 25 cycles for the various signal functions
being sununarized below on the basis of apparatus meeting
R .S. A. specifications. The track circuits, one per block, are to
be center fed and there will consequently be two relays per track
circuit. Semaphore signals will be used At both ends of each
block for each direction of traffic and similarly two light sig-
nals will be used in each block as intermediates, one for each
direction. This example may therefore be considered as
fairly representative as it covers most of the combinations
usually met with.

Functions

No.

Power per
Unit

To-
tal
V.A.

P.P.

Watts

R.F.

Re-
act.
V.A.

Volts

A°Vs

Track Circuit
6300' long

Track Circuit
16000' long

Track Circuit
17000' long

Track Relay

.> locals
^,Line Relays

Signal Slot Coils

Light signals

Sema. & switch
Tramps

Station Lamps

LineTransformer

T ^oe<» J Iron
i^osses 1 Copper

Track

Transformer

L<«^{JS'pVr

10
10
10
10

19
32

6
6

5
5

4.1

10.75

13.0

110
110
110
110

110
110

16.8

19.0

0.33
0.12
0.33
0.50

0.26
0.56

180

741

363
132
363

■ • • •

• • • •

260

.50

.54

.55

.70
.52
.50
1.0

1.0
1.0

0.3

408

254

182

550

533
1936

78
114

175
36

.87
.84
.83

.71

.86
.87

152

615

258
114
316

.96

250

1 0

875

0.2
1.0

.98

858

Total load, all
signals clear

5157

.864

4454

. 504 2599

Signal Motors, all
clearing

110

1.9

2090

.53

1108

.85

1776

Total load,
all signals
clearing

• • • •

7076

.79

5562

.62

4375

The headings of the above colunuis are self-explanatory,
excepting |>erhaps those of the last two. The next to the last
column is headed R. F., meaning Readcaice FcuAor, which is
simply sinO and when multiplied into the voltamperes V. A.
in colunui five, gives the watdess power in the last colunm,
headed Reactance VoUamperes, just in the same manner as the

TRANSMISSION SYSTEMS. 321

product of the power factor (P. F. = cos 0 ) in column six, by
the voltamperes in column five gives the true power in watts
in column seven; complete tables of cosines with their cor-
responding sines will be found in the back of the book. In
determining the total power for the system it is not permissi-
ble to add up directly the figures in the voltampere column^
because of the widely differing power factors; hence the volt-
amperes for the individual functicxis are split up into watts
and reactance voltamperes, so that a direct addition may be
made, the total voltamperes being simply the square root of
the sum of the squares of the watts and reactance volt-
amperes. Knowing the total voltamperes and total watts,
the power factor for the entire load can then be found, this
P. F. being the ratio of total watts to total voltamperes.

As regards the track circuit power given opposite the first
three items, this can be calculated, if not already known, by
the method described in Chapter XIII. The power data for
the track relays, line relays, signal sets, etc., will be furnished
by the manufacturer; representative information of this
kind will be found in the corresftonding chapters in this book.
Likewise, data covering the transformer losses will be fur-
nished by the manufacturer: however, if the trcmsformers
are available for test, the iron loss (constant at all
loads) can readily be determined by measuring with a
wattmeter the primary input with the secondary open cir-
cuited and then deducting the corresponding primary copper
loss, this being simply I ^ R, I r^resenting the primary no
load current and R the primary resistance, determined by a
D. C. Ohm's Law measurement. The secrondary resistcmce
may likewise be found and thus the total copper loss in both
primary and secondary at the given load can readily be com-
puted, the iron loss remaining constcoit. For a full discus-
sion of these characteristics of transformers see Chapter VI.

Proceeding now to the transmission design proper, it is
first apparent that the signal load is distributed fairly evenly
all along the line, instead of being coticentrated at the ex-
treme end as in the ideal cases thus far considered. With a
signal transmission the line current is heaviest near the power
house because that part of the line carries practically the
entire load, the current in the line falling otf gradually as one
proceeds from the power house; With such an even distribu-

322 ALTERNATING CURRENT SIGNALING.

- - m ■ ■_■ III II — J

tion as this* it is perfectly allowable to consider the entire load
as being concentrated at the middle of the line, this being the
point of average current and voltage. So that, although the
transmission in the present case is actually 1 5 miles long from
the power house to the extreme end of the line, the calcula-*
tions should be made on the basis of the total load being con-
centrated at the end of a line 7-| miles long, the two wires for
this distance having a combined length of 1 5 miles, or 79,000
feet. Itwilleasily be found after a few trial calculations, as
previously outlined, that, on the basis of 1 0 per cent, voltage
line loss with the signals clear, a 2200 volt tiansmission would
seem quite feasible: this means 2000 Volts at the load since

p p

Percent line loss = ^ „ ^

where Eq = volts at generator end and E^ = volts at load end

and the calculations will, therefore, be made on this basis.

Referring now to equations (2), (3) and (4) above, and Fig.

181, we have:

E^ = 2000 volts at the load signals clear

P = 4454 watts at the load signals clear

Cos 0 = 0.864 P. F. at the ]oad signals clear

Eo= 2200 volts with line drop = 200 volts (10

per cent, of 2000).

Frequency = 25 cycles ,

Distance = 7.5 miles (79.000 ft. total line wire)

Wire spacing = 1 2 inches

From the fact that

P watts = I El cos 9

4454 = 1 X 2000 X 0.864

4454

I = ;i7^7^x ^ oyj. = 2.58 amperes line current

ZUUU X U.004

Solving for the trial resistance R^ , knowing the line drop (200
volts):

IRi = 200
2.58 Ri = 200

Rj = 77!5 ohms

This figure of 77.5 ohms is to cover a total of fifteen miles
(79,000 feet) of wire, and, from the wire table, will be found
to correspond closely to No. 10 B. & S. Copper wire, whose
reactance X per mile on 25 cycles^ with wires spaced 12 inches

TRANSMISSION SYSTEMS. 323

on centers, is 0.2889 ohm, or a total of 4.3 ohms for 1 5 miles,,
as given in Table III. Now:

El cose =2000x0.864= 1728 volts

and El sine + XI = (2000 x 0.504)+ (4.3 x 2.58) = 1019
volts

From equation (4) above

R= VEq^ - (El sin e + XI)^- Eicos e

of which all the quantities are now known, and the true re-
sistance R of the 79.000 feet of wire is discovered to be 86
ohms; this corresponds to a solid copper wire size between
No. 10 and No. 11 B. & S.. and therefore No. 10, the nearest
larger size should be chosen.

To determine the total power delivered to the line at the
generator end, this being the sum of P and the line losses,
proceed as follows: The quantity (Ei sin e + XI), equal
to 1 019 volts, represents the watdess volts delivered to the line
at the power house. The quantity (Ej cos e -f- RI). equal
to 1931 volts (for No. 10 copper) represents the power volts
delivered to the line. The sum

Eo = \/(Ei sin e + XI) 2 4- (El cos 0 + RI)2,

equal to 2183 volts, is the total volts Eq at the generator.
The power factor of the power house load is the ratio of the
power volts to the total volts E^ and, in the present case, is
1931 divided by 2183 or 0.884. The line current, as solved
for above, was found to be 2.58 amperes and with an initial
voltage of Kq = 2 1 83 fed to the line, the load at the power
house becomes simply 2.58x2183 = 5.63 K. V. A. or 4.98
K. W. at 0.88 P. F. It is to be noted that due to the employ-
ment of No. 1 0 line wire, which is a litde larger than theoreti-
cally necessary, the required voltage at the generator end of
the line is only 2183 volts instead of 2200 volts as originally
assumed: the percentage line loss is therefore decreased to
9.2 per cent.

Knowing the current and the load voltage with all signals
clear, the corresponding generator voltage E^ could also have
been found by considering the load as an impedance of Z^ ohms
whose components X^ and Rj^ could have been determined,
knowing the power and reactance factors of the load; knowing
the line impedance and the load impedance, the total iipped-

324 ALTERNATING CURRENT SIGNALING.

T_ . . - - -

ance Zq of the line and load combined could have been fovind,
and from this the impressed generator voltage would have
been E^ = 12^ where I is the line current of 2.58 amps.

To illustrate this method, let us determine the total power
at the generator and the percentage line drop with all signals
clearing simultaneously. In our power summary we figured
that with 1 1 0 volts on the line transformer secondaries the
power required at the load with all signals clear would be
5157 V. A. at 0.86 P. F. and with 2000 volts at the load the
generator voltage E^ would be 2183 volts; similarly we cal-
culated that with 1 1 0 volts on the signal motors (2000 volts
at the load) the power at the load with all signals clearing
would be 7076 V. A. at 0.79 power factor and 0.62 reactance
factor, the corresponding line current at this voltage being

' ~ 2000 ~ ^-^ ""P^

The equivalent impedance of this load would be

E 2000

7 = >-- = . s= 565 ohms

^' 1 3.54

Now from the power summary cose = 0.79 and sin 9
= 0.62, and referring to equations (13) to (20) in Chapter II

Rl Rl

Sine =vgr^=^'=0.62

Where Rl, Xl and Z^ are respectively the equivalent resist-
ance reactance and impedance of the **all clearing" signal load.
.-. Rl = 0.79 X Zl = 0.79 x 565 = 446 ohms
.-. Xl = 0.62 X Zl = 0.62 x 565 = 350 ohms
Now we found in calculating the line that its resistance r is 79
ohms and its reactance x is 4.3 ohms; hence, representing the
total resistance, reactance and impedeuice of the combined
line and load* acting as one circuit, as Rq, Xoand 2^ respec-
tively,

Ro= R^ + r = 446 + 79 = 525 ohms
Xo= Xl -h X = 350 + 4.3 = 354.3 ohms
Zo = VR<? + XS= V(525)2 ^ (354.3)2
= 633 ohms
and since the impressed generator vcdtage E = 2183

TRANSMISSION SYSTEMS. 325

Eo 2183_
'» ZT " ^633 - ^-^^ "^P^
and the total load at the power house becoities
Eo lo = 2183 X 3.45 = 7.53 K. V. A.
The power factor of the combined line and load is

^ ® = § = n = <^»^

and the total load at the generator in kilowatts is

7.53 X 0.83 = 6.25 K. W.
With a load current of Iq = 3.45 amperes as above deter-
mined* the volts at the load El^is

El= I^jZl = 3.45 X 565 = 1949 volts

,. , 2183-1949 ,^
Percentage line loss = toAQ — ~ i2 per cent.

Therefore, if the secondaries of the line transformers give 1 1 0
volts with a primary "all clear" voltage of 2000, when all sig-
nals are clearing the transformer secondary voltage will fall to

1949

2nn(\ X 1 10 = 107.2 volts; the signals immediately in the vi-
cinity of the power house would of course be supplied with a
higher voltage than this since the line drop is small near the
power house, increasing to its maximum of 12 per cent, at
the end of the line farthest from the power house.

The power generating apparatus and tnain step up trans-
former in the power house must, of course, be of sufficient
capacity to handle the maximum "all clearing l*oad"; due how-
ever to the short duration of this maximum load the power
apparatus will in most cases be satisfactory if rated at 75 per
cent, of the "all clearing'* K. V. A., provided, naturally, that
the regulation of the generator and the transformer is not
excessively poor. In the present instance the nearest ap-
propriate commercial size of transformer will be found from
the list on page 205 to be 7.5 K. V. A.

SINGLE PHASE VERSUS POLYPHASE
TRANSMISSION.

9* Single-Phase Systems. The system we have thus
far discussed, that shown in Fig. 182 (a)« is known as Single
Phase Transmission and it is the simplest of all tremsmissions.
Summarized its characteristics are as follows:

M6 ALTERNATING CURRENT SlCih4ALlNC.

1. Two line wires the length of the •ystem.

2. Power deUvered W = E^ I on non-inductive load.

or W = Ej 1 cos 8 on inductive load,
where Eg = load voltage and 6 is the phase angle be-
tween 1 the toad current and E, .

3. Power lost in transmiasioD = 2I'r where r is the re-
nstance of each line conductor.

4. But Mie ample tronsfoimer is required at each signal

I W I

C 'step UP Fua CUT ooT-T-t f ,

U^ mUKFOKUCK ♦*4 H+

'y LIQHTNMa AMtESTBT SSS—^

oeH^ATW ^-^

^ * Vtd ii

10. Polyphase Systems. A polyphase power transmis'
sion insy with advantage be employed in those coBes in A. C.
signaling where the system is an extensive one and power has
to be transmitted over a distance of . say. 1 00 miles or overftom
one central power station; here, with a given amount of power
to be tTBDBmitted over a stated distance at a given ventage
and percentage line loss, a polyphase power transmissitHi will
require leM line copier, and will, furthermore, lend itsdf

TRANSMISSION SYSTEMS.

327

readily to the economical use of induction signal motors, as
described in chapter VII 1.

The generation of polyphase currents is a very simple, fbat-
ter, the object in view being the production of two or more
currents differing in phase by some convenient amount,
usually 90 degrees or 120 degrees. To obtain two currents
90 degrees apart, as in a two-phase system, it is only necessary
to provide the armature of the alternator with two separate
windings placed in the slots 90 electrical degrees apart, so
that when the voltage generated in one winding is a maxi-
mum, the voltage in the other coil is zero, as indicated in (a)
Fig. 183. To obtain three voltages 120 degrees apart for a
three-phase system, three separate windings are employed,
spaced and connected to give voltages as shown in (b) Fig.
183.

(a)TWO-PHASE VOLTAGES

(b)THREE-PHASE VOLTAGES

C A C

Fig. 183. Wave Traces of Two-Phaae and Three-PhaM Voltage*.

With a three-phase arrangement as described, it is usual
to connect the armature windings so that only three trans-
mission wires will be required, this resulting in increased cop-
per economy, as will presently be shown. The two most
general methods of connecting the three windings are known
as the st£ir connection Fig. 1 84, and the delta or mesh connec-
tion, shown in Fig. 185.

528

ALTERNATING CURRENT SIGNALING.

,,, 1|* Three^pha«e Star. In the star connection, each of
the three armature windings is brought to a conunon junc-
tion point, the netdred, and the three remaining ends are con-
nected to the'eutgoing wires by slip rings carried on the arma-
ture shaft. Tlie three lines A, B cknd C, in (a) Fig. 184, then
serve, in turn* as the outgoing and incoming return circuit,
the maximum current shifting in regidar rotation from ooe
to the others, as shown in (b) Fig. 163, 'The«ame voltage,
say 1000 volts, is generated in each of the coils a* b and

-►A

^AB"^oa"Eob*Eoa+Ebo
^Bc"Eob"Eoc"^ob"''^co
EcA"Eoc"Eoa"Eoc"^Eao

Fif. 184. Vector Diafimm of Currents and Voltages in Tbree-Pbaae Star

System.

TRANSMISSION SYSTEMS. 12^

e» Fig. td4. but these voltages are 120 degrees apart, so that
while the voltage between neutral point o and each of the
lines A, B and C will be 1 000 volts, the voltage across A and
B, B and C» and C and A, will be the vectorial sum of the
equal voltages induced in the two coils across which each pair
of mains is connected. Due to the shifting direction of the
voltages generated in the three coils» their vectors must be
added with proper attention to their algebraic sign, the nota-
tion of the diagram at the right of Fig. 184 being such that
when the voltage generated in coil a tends to send a current
outward from o along a that voltage is designated as E^i^.
Now, when the voltages in coils a and b are to be
c;ombined vectorially, it must be noted that they are act-
ing in opposite directions from the neutral point o, so
that they really have to be subtracted; in other words;
if voltages E^n and E^b stre to be added with due attention to
their sign, E^b must be extended backwards on itself, so that
it can be added to Eloa, a<xording to the usual parallelogram
of forces, in which event the resultant Voltage across the
mains becomes.

EaB = Eoa — Eob = Eoa + Ebo
Ebo =7 E^b — Eoo = Eob + Eoo

In magnitude, these resultant voltages ap6 simply tne long
nde of a 120^ triangle and are, therefore, y/3 = 1.732 times
the length of either of the short legs composed by the coil
Vintage vectors. We started out with thie assumption that
each coil voltage was 1000 volts; the voltage across any two
the mains is, therefore, -y/S x 1000 volts ?= 1,732 volts.

On a non-inductive load the currents flowing in each of the
coils a, b and c are, of course, in phase with the coil voltages
and since the current in each main flows right out of the coil
to which it is connected, it follows that the currents I^^, Igand
Iq in the mains are in phase with their respective c;oil voltage
Eoa> Eob s^d Eoo* as shown. On a highly induc^ve load such
as met with in signal work, the current lags behind the volt-
age and if the phases are equally loaded, the fine currents
^AL* ^BL «^^ ^OL ^^ lag e degrees behind, their respective coil
voltages, e beingtheangleof thelagof theload. Inthiscase*

530 ALTERNATING CURRENT SIGNALING*

the pcywer ddivered by one coil is one-third the total power W.
W = 3 IalxcosO xEoi

but Eoa= —7^

.-. W = 3 Ialx cos e X H^

Eab

. Eab V3 Eab _ V3 Eab
and since —y^- -=^ -tz -;z

V3 V3 X V3 3

W = VFEab Ial cos e
/. W = V3 E I cos e
where E and I are the line voltages and currents, respec-
tively.

12. Three-phase Delta. With the more common E>elta;
or Mesh connection Fig. 185, the six terminals of the three
generator windings are connected two and two, the junction
points of the windings being connected to the outgoing lines.
Here, each coil generates the full voltage between the pair of
mains to which it is connected, but the current in any line,
as B, is the vectorial sum of the currents in the coils c and h^
differing in phase by 1 20 degrees, just as the voltages between
the mains with a star connection is made up of the vectorial
sum of the two coil voltages. The current in B is, therefore,
\/3 times the current in coils c or h, and so on for the other
lines A and C. In the delta connection, therefore, we deal
with resultant currents, just as in the star connection we deal
with resultant voltages. Here, again, on a balanced non-
inductive load, coil c would deliver one-third of the total
power to the system; the total power would, therefore, be:

W = 3 Ioo^Eab

V3^

but loo ~

J Ibx V3 = V3 Ib
• V3 V3 3

.-. W = V3 EabIb _
and. in general, W = V3 E I
wh«re E and I are the line voltages and currents, respectively.
Ob an inductive load, l^ laff< ^V ^ degrees behind the line

TRANSMISSION SYSTE^4S.

331

voltage, and. therefore, the component of the coil current in
phase vdth the voltage becomes looL ^^^ ^

and W = VJ EI cos e«
The delta connection is generally emplo3red in signal work,
especially in connecting transformer coils, as shown in Fig.
182 {b\ for the reason that if one of the transformer coils
bums out the other two will handle the load, although the
system will be unbalcmced; with the star connection, one of
the mains would be entirely dead if the transformer coil
connected to it were burned out.

A—*

Ic"' Ob "'oa"^ob '^^ao

Fig. 185. Vector Diagram of Currents and Voltages in Three-Phase Def

System.

332 ALTERNATING CURRENT SIGNALING.

13. Cot>per Economy of Three-Phase System* The
three-phaae tiansmiasion system has the remarkable prop-
erty that only 75 per cent, as much copper is required to de-
liver a given amount of power with a stated transmisaon
voltage, loss and distance, as in the single-phase system.
Assume, for example, a three-phase sjrstem carrying a non-
inductive load with E volts between mains, the current in each
main being I, and the resistance per line wire R. Then, for a
star connection, as we have seen, the voltage in each gener-

E
ator coil is — ;=, the current in each coil is I (the same as the

line current), the power delivered to each branch by the coil ta

EI •v/'^ 17 f

which it is connected is .— , or ~ , and, since there are

V3 3

three branches, the total power delivered to the system is

VF EI —

3 r f or \/3 EI. Similarly, with the delta connection,

the stated voltage across the mains being E as before, the coil

current, as previously shown, is — 7=, where I is the line cur-

rent, and hence, the power delivered by each coil to the cir-

.,. EI V3EI,
cuit IS T^.or r the total power delivered by the three

3 v^3 EI / —

coils to the system being , or v 3 EI, as with the

star connection.

The loss in each line, with either star or delta connection,
is obviously 1 ^ R, I being the current line, this latter quantity
being the same ia aH cases. Then the total line loss will be
3 P R, since there are three wires. Now, let the same amount
of power, VB EI, be transmitted by a single- phase system at
a transmission voltage of E volts. The current will, evident-
ly, have to be I V3. Let R^ be the resistance of each of the
single-phase wires, such that the total line loss willbe3 P R,
as with the three-phase system. The resistance of the com*
*^te single-phase circuit will be 2 R^ , and the total loss with
TamperesflowingwiUbe (I V3)«x 2 Ri=* 6 P Rj, But

TRANSMISSION SYSTEMS. 333

since it is stipulated that the loss single-phase shall equal the
loss three-phase,

6 12Ri = 3 P R

_R
.. Ki - 2

that is, the resistance of each of the single phase wires will be
just one-half of the resistance of each of the three-phase wires.
The cross-section of each single-phase wire will, then, be
twice the cross-section of each three-phase wire. If the weight
of each of the three-phase wires is W, the total weight for the
three-phase line will be 3 W, while the total weight of the two
single-phase mains of double cross-section will, evidently, be
4 W for the same length of transmission. Hence, the three-
phase system requires only 75 per cent as much copp>er as the
single-phase system.

14. Relative Advantages of Single and Three-Phase
Ssrstems. The copper economy of the three-phase trans-
system makes it very attractive, and it is now coming into
use in signal work where power has to be transmitted, say, a
distance of fifty miles or over, and p>articularly where there is
a considerable station lighting load in addition to the signal
load; for short lines, the calculations will often indicate a wire
size too small for mechanical strength, in which case, of
course, a single-phase transmission ought to be used, as the
third wire for the three-phase system would be an absolute
loss.

Referring to (b) Fig. 182, showing a straight three-phase
delta system, the step-up in transformation at the power
house may be effected by three ordinary single-phase trans-
formers, vrith their primaries (inside the triangle) and their
secondaries (outside the triangle) connected as shown; or,
again, a special three-phase transformer may be used, its core
having three legs, on each of which a primary and its second-
ary may be threaded. The same statements apply to the
step-down transformers required at the signal locations along
the line. From this, it will be seen that the use of a straight
three-phase system has the drawback that at each location
either three single-phase transformers are required or one
special three-phase one. This fact also complicates matters,
in that extra fuse cut-outs are required for ctisconnectinf the

334 ALTERNATING CURRENT SIGNALING.

^1" ■ I I .,,.>,. I ^ ■■■■■■■ ■ .— »

transforming apparatus from the line. The amount of extra
app>aratus required in the way of transformers, fuse cut-outs
and lightning arresters is a serious drawback to the straight-
three-phase system, but» on long lines, or where there is con-
siderable load to be carried, it will generally be found that a
three-phase transmission is the cheapest, particularly if some
scheme can be found whereby the number of transformers at
each signal location can be cut down.

PHASE TRANSFORMATION.

15. Three-Phase to Two-Phase ; Scott "T" Connection.

In addition to representing the voltages in a three-phase sys-
tem by three radiating vectors 120^ apart, as shown in Figs.
184 cmd 185, it is perfectly feasible to represent these voltages
by the sides of an equilateral triangle A^BjCi shown at (c)
in Fig. 182, providing the direction of the voltages is properly
indicated by arrows as shown; this triangle diagram cor-
responds exactly to those with the radiating vectors shown in
Figs. 184 and 183. for if the vectors in triangle A^ , B^ Ciof (c)
Fig. 182 are projected in the direction of the arrows from any
single vertex, representing the origin of Figs. 184 or 183, it
will be found that three radiating vectors 120*^ apart are the
result.

Suppose, now, that we connect two transformers to a set
of three-phase mains, as shown in (c) Fig. 182, where one ter-
minal O is of one primary P is connected to the middle point of
the other primary M, and, furthermore, let us provide pri-

vr.

mary P with '-~j~ times as many turns as M. Since M is con-
nected across mains B and C, its voltage is represented by vec-
tor BjCx in the diagram at the left of Fig. 182 (c), and, since
one terminal O of primary P is joined to the middle point of
coil M, one end of the vector representing the voltage across P
can logically be placed at O^. As regards the placing of the
other end of this latter vector, it must be remembered that

we intentionally provided P with— times as many turns as

M, or. what is the same thing, V3 times the turns in each
half of M: we are, therefore, justified in placing the outer end

TRANSMISSION SYSTEMS 335

of the vector representing the voltage of P at A ^, since the
long leg O^A^ of the60° triangle O^ A ^B^ isV3 times the short
leg 0 1 B ^ . Finally, then, the three-phase vectors A^B^.B^C^
and C^ A^, which we originally started out with, are now
resolved into the three component vectors B^O^, O^C^ and
O ^ A ^ , the original vector A ^ B ^ . for example, being the result-
antof B^O^ andO^A^

It is to be noted from the diagram that O^A^ is separated
by 90° degrees from B^O^ and O^C^, and for this reason, the
voltages induced in the corresponding secondaries Q and N
are 90*^ out of phase. These two transformers in Fig. 182 (c)
therefore deliver pure two-phase currents from their second-
aries, Q and N , and we are thus permitted to use two-phase induc-
tion motors which, on account of their freedom from artificial
phase splitting devices, such as have to be used in single-phase
induction motors, are much more eccmomical than the latter.
The track circuit app>aratus and the signal slots and lights
are, of course, single-phase devices, and, in feeding them, they
should be divided up between secondaries Q and N so as to
balance the load on the primaries. This ingenious scheme
was invented by C. F. Scott, and is, hence, known as the
Scott or **T** connection. It provides a means whereby we
.may take advantage of the copper saving effected by a three-
phase transmission, while still requiring only two transform-
ers at each signal location.

16. Three-phase to Single-Phase. Another scheme
whereby the number of transformers at signal locations may
be cut down, where a three-phase transmission is used, con-
sists in dividing the transmission into three equal lengths,
feeding all signals on the first section from single-phase trans-
formers connected to one phase, the signals on the second sec-
tion from the second phase, and the signals on the remcuning
stretch from the third phase, thus approximately balancing
the load. With this arrangement, the only disadvantage is
that single-phase motors must of course be used, and if they
are of the induction type they will not be so economical as
polyphase motors. However, the extreme simplicity of the
scheme in the way of apparatus makes it of great merit and it
will probably see extensive use on long lines. p>articularly if
the balancing of the load between phases can be improved by

ALTERNATING CURRDJT SlCNAUNa

a wdl distributed itation lighting component or otker tuch
power load.

PRACTICAL CONSIDERATIONS.
The Line.

17. Aerial Line Materials. Either copper or aluminum
may be used, but it is probably safe to assert that, apart from
the question of cost, the high conductivity combined with the
great strength and clastaGity of hard drawn copper, give this
material an advantage over all others for um on high tension
tranuniMionfl. Tlie relative properties of copper and alum-
inum are given in the Table VI below:

TABLE VI.

Stranded Aluminum and Solid Hard Drawn Copper
Compared. The commercial sizes of stranded alumiaum
cables made by the Aluminum Company of America are not
even circular mil and B. & S. sizes, but are of such cross sec-
tion as to give the same conductivity as even circular mil and
B. & S. sizes of copper cables of 97 per cent, conductivity.
The resistances below given for copper apply to hard drawn
line wire whose conductivity is somewhat less than that of
ordinary soft drawn copper wire.

TRANSMISSION SYSTENffSL 3S7

The conductivity of hard drawn aluminum wire is between
60 per cent. and6l^ per cent, of pure copper. The weight
of an aluminum conductor is about 49 per cent of that of a
copper conductor of equal resistance, and is about 73 per cent,
as strong, in safe working stress, as the equivalent copper
wire. Comparing aluminum of 61 per cent conductivity with
copper of 97 per cent, conductivity, the diameter of the
equivalent aluminum conductor would be 1 .28 times the diam*
eter of the copp>er wire. The average breaking stress of hard
drawn aluminum is between 23,000 and 30,000 pounds per
square inch, depending on size and hardness; for copper, the av
erage breaking stress varies from 30,000 to 62,000 pounds per
square inch. The average maximum working stresses for
aluminum and copper are generally placed as 13,000 and
28,000 pounds per square inch, respectively. Aluminum
cannot be soldered, and, where taps have to be made, a bolted
or damped construction must be resorted to; in cases of splic-*
es in the line, a special double aluminum sleeve for twisting the
two conductors is employed. Finally, for equal conductance,
aluminum is cheaper than copper, the price being held, by
those in control of the market, about 1 0 per cent, less than cop-
per; on account of this artificial cost, the scrap value of alum-
inum is very questionable, whereas copper may be consid-
ered as a fair investment, its scrap value being high.

Aluminum line vrire for transmissions had best always be
stranded, as a cable composed of a number of small wires is
stronger than an equivalent solid wire. Due to its low
tensile strength aluminum cannot well be used in the smaller
wire sizes, but in sizes corresponding to conductivities of No.
6 B. & S. copper, it can be stranded and oftentimes provided
with a steel core, so that it will be sufficiently strong and stiU
cheaper than copper.

18. Stringing, Pole Spacing and Wire Spacing. The

most important point in the design of aerial lines is to obtain
a strong construction, so that the line will stand up under the
severest weather conditions. This means, especially that the
wire must be large enough, mechanically, to have a good fac-
tor of safety: smaller wires than No, 10 hard dumn copper
or No, 12 copper clad should never be used. In stringing the
wire, one need merely make the span tight enough to aver

IM ALTERNATING CURRENT SrCNALING.

risk of the vfire* •winging together. Any tights Btringiag
is a conceanon to appearance, and may lead to a break dur-
ing a severe atomt. particularly during cold weather, when
the wire contracts. [Reflections of 2 per cent, or three per
pent, at normal temperatures are none too great for most
situations. IDepending on the size and kind of wire used, the
poles shouM be spaced from 150 feet to 200 feet apart, the
ionaei figure bung generally employed on those signal trans-
missions where hard drawn copper is used. On account of
its lesaer weight for equal conductivity, aluminum wire will
allow of a greater pole spacing than copper, particularly if the
aluminum is stranded and provided with a steel core; for eu-
ample, on one long signal transmission which the author has
in mind, a No. 4 B. & S. stranded aluminum steel core cable
is used, and. in this case, the poles were spaced 200 feet apart.
For 2200 volt work, the wires should never be spaced less
than )2", and preferably 13" or 18", to avoid thar swinging
together in a high wind and with loose stringing. For 4400
volts, a 24"-28" spacing is considered good practice.

1 9. Underground Lines. Here the line is generally laid
in creoBoted trunking buried about two and one-half feet
below the surface of the ground, the wires being, of course,
pitched ini Fig. 186 illustrates a construction of this kind.

First, a layer of

- 2V— pitch about H"
thick is poured
into the trunk-
ingasan insulat-
ing bed, after
which the wires
are laid and
finally pitched

ought to belaid
close txigether
(there is a dou-
ble wall of rub-
ber t insulation
between them), for this provides for a good layer of pitch
between the sides of the trunking and wires. In the ctmstruc-

TRANSMISSION SYSTEMS. M»

tion shown in Fig. 166, the wires were of No. 4 stranded
copper, extra heavily insulated and carried the entire power
at 3300 volts for a twenty mile stretch of double tracli sig-
naling with considerable margin in conductivity. The con-
duit was laid in 2000-foot lengths snd connection^ made in
concrete junction boxes by Dossert connectora. flic secret
of successful construction of this kind lies i* careful
instnllatioo.

20. Sectionalizjng. In order to avtnd traffic delays due
to breakdowns in the line, the latter oi^ht to be divided into
sections and sectionolizing switches (usipally oil immersed and
hung at the top of the pole) installed at the junctian points,
BO that the sectian in trouble may be cut out (or repairs, the
Une in the meantime, being fed from both ends up to the dead
section: with this provision, only those signals fed by the dead
section will be out of service. If the line is a very bnportont
one, sectionalizing switches may be H^talled at each signal
location; otherwise, every five miles to right miles.

Fia. 187. Poicelua Fiue Cut-Out f« 2Z00 Vdt LinM.

21. Fuse Cut-outs. It is often necessary to temporarily
disconnect a line transformer from the transmissitHi, and it is
furthermore advisable to protect the line-;from a short-circuit
in case the primary coils of the transformer should them-
selves become ahort-circuited, due to on insulation break-
down following a lightning discbarge, for example. For this

3W ALTERNATING CURRENT SIGNALING.

purpose, a fuM cutout. Fig. 187 for 2200 volt work, or Fig.

168 for' voltages higher than 2200, is inserted in each primary
lead wire, the fuse cut'
outs being attached to
the croBB-arm on either
side of the transformer,
on the pole. The 2200
volt cutout Fig. IS7
consists of a porcelain
block at the left of the
photograph, into which
the T;A\ig in the middle
is aUppcd. being held
there by a spring catch
released by a twist of
the plug. The plug
carries a long (use wire

minala. which close the
circuit when the plug
is inserted in its holder,
as shown at the right
of the figure. The plug
ia a solid block of
glazed porcelain „ so
that there is no chance
of one being shocked
when it is desired to

former from the line.
Tlie cutout shown in
Fig. 188 is spoken of as
the "expulsion type,"
and is intended for

^^' '®*U™ov^Z200 Vo*rw'"°"'*" ^l*^** "^i" 2200; it
consists of a long fuse
carried in a vertical fibre tube, the sudden expansion of the
air in the tube, due to headng when the fuse blows, being
utilized to blow out the arc. The fuse is removed from it*
bolder by simply pulling the door of the box open as diown
in the t^iotograph. The wooden box canyiog the fuse it to

TRANSMISSION SYSTEMS. 341

be nailed to the cr(MB-B.rm near the tranafonner; one fuM
should be provided for each primary lead.

22. Lishtning Protection Alons the Trananiittlon.
It is customaTy to install lightning arresters on the line at
each tranafonner location, one lightning arrester being
provided for each primary lead of the transformer to
be protected. For line voltages up to 2200. the well
known Compression Chamber Multigap arrester Fig. 189,
may be used, this arrester consisting simply of a series of
short spark gaps in series with a resistance rod, all slipped into
B porcelain tube as shown at the right of Fig. 169. As will
be evident from this latter cross section, the spark gape
occur between a number of buttcoi shaped units; these units
I are made of a special
n<Hi'arcing zinc alloy.
In the 2200 volt ar-
rester illustrated there
arecightgaps. Briefly,
the action is as follows:
When excess potett-
tial tm the line, due to
lightning or similar
causes, reaches a value
high enough to cause
the row of air gape to
break down, a flow of
current occurs through
the arrester to ground,
. R«. 189 Comp™««. Cl..mb.r Light- "^eving the line of the
nint Arrcitei AHcmblisd Complcts dangerous potential,
■nd in Swiion. Immediately after this

current has passed, the Une current, due to the fact that a
path has been established through the air gapa. begins to
flow through the arrester. The first flow of current has,
however, generated ziitc vapor which has, although in a lesser
degree, the sntne cjuality as mercury vapor, namely, that of
rectificatidD of the dectric current, or allowing the CUrrtttt
to flow only in one direction. Hence the line current follow-
ing the discharge flows only until the vintage wave reverses,
in other words, until the end of the half cycle, whereupon i'

J42 ALTERNATING CURRENT SIGNALING.

is preveoted from rever«ing by the rectifying acticn of
these gaaes.

It will be noticed tn Fig. 189 that the zinc alloy elec-
trodes with the small porcelain separatore make a small closed
cluunber. During a diBchargc the gases formed by the arc ara
held vrithin these chambers, become slightly compressed and
assist in extinguishing the arc by partially smothering it.
This feature gives the arrester its name. An arrester is re-
quired for each primary lead of the transformer to be pro-
tected and the arresters may conveniently be placed on the
fame cross-arm as the transformer, one on either side in the
case ot single-phase lines.

For lines of higher voltages, the so-called Graded Shunt er-
tester. Fig. 190, is considered standard. This latter arrester
is umilar to the Compression Chamber type previously de-
scribed, but, in addition, is provided with two or more carbon
rods of high resistance cotmected in shunt across a number of
gaps between the
cylinders, so that
minor static dis-

line may find
ground through '
the carbon rods,
with one or two
gaps in series, but
without having to
leap the whole

gaps; heavy dis^
charges of high
potential, on the
other h-ind, will
force their way
Fif. 190. Gilded Shunt Multiup Lithtnini across th& whole

The arrester is housed in a wooden box and is to be attached,
one for each primary transformer lead, to the cross-arm
•Upporting the transformer.

A good ground for the arresters above described is formed
by a I " galvanized iron rod or pipe about B ft. \q^ driven

TRANSMrSSICtfJ STrBTEMS, M3

into the gTound. The leaxl betwreen the amBter nnd Brouttd
■hould he as straight as is possible to make it, without Idnka
or bends.

23. lnsulatora> At ntcnature condenses on the insida
•urfaces o( glass insulaton more readily than is the case with
porcelain, and, as the latter, moreover, is capable of withstand-
ing sudden strains better than glass, most insulators for high
tension lines are made of porcdain.

Fig. 191. Main Powa HouHiSMtdilHRl HumIIuk Dui>lic4» CiuHin
Sttt, Slap-up Truutonnan and Two Sat> at Oatwaint Maiiu.

344

ALTERNATING CURRENT SIGNALING.

POWER EQUIPMENT.

24* Elements. The apparatus in the power house con-
sists of the engines, generators, switchboard equipment, and
main lightning arresters. Continuity of service is of prime
importance, and therefore, duplicate apparatus ought to be in-
stalled, unless some reliable source of commercial power is
available.

25. Switchboard Equipment. Fig. 191 is a photograph
of a stcmdard switchboard providing switching facilities for
duplicate engine driven generators feeding duplicate step-up
transformers, supplying power to two sets of outgoing high

A.C.BUS MAINS

Fig. 192. Schematic Circuit Diagrain for Main Swritchboard

Shown in Fig. 191.

voltage mains working single-phase. A simplified wiring
scheme of this board is shown in Fig, 192. The board cob-
sistsof three panels, the two panels at the left being duplicates,
one for each generator and transformer set, while the remain-
ing right hand p>anel controls the two sets of outgoing mains.
At the top of each generator p>anel is the Tirril regulator con-
nected by a local circuit (not shown, to simplify diagram) to
the generator field, and automatically regulating the gener-
ator voltage, so that the latter will be constant. Below the
Tirril regulator is the ammeter A, Fig. 192, indicating the cur-

TRAN»rflSSION SYSTEMS. 345

rent output of the generator, and, on either dde of the am-
meter, ore the plug switches E, hy means of which the mnin
•tq>-up tranaformei T may be disconnected from the busbera
after the oil switch G has been opened; the plug mvitchca
themselves are<Hily intended I oi Lipening the arcuit when it
is once dead. The handle for the generator field rheostat is
next below the nimneter, and sdtt farther down, at the bot-
tom of the board, is the handle of the oil switch G for (qjening
the gBienitor circuit.

Id transferring the load from one gaientor to the other in
case of shut down, the incoming generator, which is to take
up the load, must first be brought up to voltage and in phase
with the generator carrying the load before the incoming ma-
chine may be connected to the busses. This operation is
called tynchranizing, and h synchronizing meter at the Uip
oi a small swioKing panel, at the extreme upper left of the
switchboard, indicates when the incoming machine is up to
speed, the needle pointing to "Fast" or "Slow", depending
upon the speed of the incoming machine. Below the synchro-
scope are the synchronizing lamps, which are dark when the
machine- aw exactly in phase. The voltage and frequency ■
of the incoming
machine are indi'
cated. respective-
ly, by the vol tmet-
erat the bottom of
the swinging panel
and the frequency
meter directly

The outgoing
mains are control-
led from the large
panel at the right
of the board, at
the bottom of
which are the oil
switches F, in Fig.
1 92, provided with
Ft.\n. R(w«<Swiuhl»ardSI»wBiDFi«. 191. ma ovedoad trip

346 ALTERNATING CURRENT SIGNALING.

coil to Open the circuit in ca*e of & short. Above these oil
switches are the plug switches J and H; by means of these
■witches J. either or both of the outgoing lines may be diacoii'
nected from the busses; by means of the switches H. the lines
can be isolated entirdy, thus protecting theoil switches F. IE
the local power plant goes out of service, line D can be fed
from line C by opening plug switches E and reeding D from
C through I^, F and J, across the busses. At the top of
the outgoing feeder panel is a recording voltmeter drawing a
curve of the actual line voltage during the day, and on either
nde of this meter are a set of ground deteclor lamps for the
two wires of each set of outgoing mains. The liaclc of the
board is shown in Fig. 193, the oil switrches being plainly
evident at the bottom. Above the field rheostats are watt-
hour metera measuring the energy for each pair of feeders.

26. Switchboard for Interurban
Signaling Sub-Stations. The above
switchboard is intended for steam road
signaling where power has to be fur-
nished by a local set of engines and
generators. In the case of electric
roads, however. A. C. power may bo
taken directly from the A. C. side of
the rotaries in some convenient sub-
station, and in such cases the switch-
board layout is greatly simplified, as
only duplicate etep-up transformers
and the necessary meters and switches
are required. A simple hgard oE this
character ie shown in Fig. 194. the
corresponding wiring diagram being
covered by Fig. 195. The board con-
sists merely of a double-pole circuit
breaker C with an overload trip coil E
at the top of the board over which
power is brought from the A. C. side
of the sub-station rotaries to the middle
of the double-pole double-throw hand
switch B by means of which either of
"unRi^lS^^ ^ '^^"P transformers T, or T,
bond. »°^ » energized. When C optoa it

TRANSMISSION SYSTEMS.

347

HIGH TENSION
MAINS

doses the circuit for bell W» by means of contacts mad^
through the operation of bar D connected to C, and the sub*
station attendant is thus audibly warned that the line is dead.
The transformers T^ and T2 can be entirely disconnected
from the line by plug switches P. The ammeter A indicates
outgoing amperes; to avoid danger because of the high volt-
age used, the ammeter is not direcdy connected to the high
tension mains, but is fed from the secondary of a current
transformer of known ratio.

27. Lightning Arresters. Because of the value of the
power plant app>aratus and the p>aramount importance of
protecting the station from a breakdown due to lightning, a
very sensitive light-
ning arrester of
good discharge ca-
pacity is required.
For this purpose,
an arrester of the
Aluminum EJectro-
lytic type is gener-
ally connected to
the line at the power
house, Graded
Shunt, Compression
Chamber or Multi-
gap arresters being
used at the signal
locations along the
line. The aluminum
electrolytic arrest-
er, shown in Fig. 1 96,
consists of a number
of aluminum cones
piled closely one
over the other
with a »h«ht wr- ROTARY CONVERTER

gap between filled p^ ,^5 ^.^^^ ^^.^^ ^ Intemrban
with an electrolyte. Road Switchboard.

A film of aluminum hydroxide is formed on the cone*
and about 323 volts is required to break down the film on

34* ALTERNATING CURRENT SIGNALINO.

oach cone. Up thii critical voltage, the cell allows only mi
exceedinsly nnall current to pao, but when the critical
voltage is pasaed. the flow oE current ia limited only by the
ohmic resistance of the cell, which is very low. A doM
analogy to this action is
found in the safety valve on a
steam boiler, by which the
steam is confined until the
pressure rises above a cer-
tain value. With the Alum-
inumElectrolyticanesterbut
little current passes through
the cell at normal vdtagca,
but v^en the line is sub-
jected to over-vxdtoge. as in
the case of lightning, the
hydroxide film on the cone
breaks down, and the counter
action of the ceil disappears
to that the discharge passes
freely to ground. As soon
as the excess voltage dis-
appears, the film re-asserts
itsdf , and the cell acts once
more as a dosed safety
valve. For hiih transmis-
sion voltages, a number of
cones in series must be used
to secure sufficient counter
effect.

It is customary to insert a
choLe coil, consisting of a
few turns of heavy hard
drawn copper, wound in a

spiral and mounted on a porcelain or other suitable base,
between the aluminum lightning arrester and the power
apparatus; due to the great impedance of the choke coil in
the case of high frequency surges and lightning discharges,
such surges and discharges are choked back on the line so
that .they do not reach the power apparatus, but escape
over the lightning arresters.

CHAPTER X.

INTERURBAN ROAD SIGNALING.

ALTERNATING CURRENT SlCNALtNG.

urbuRocd. N«.

CHAPTER X.

INTERURBAN ROAD SIGNALING.

General Requirements. During the past ten years, the
interurban electric roads have been extended and developed to
such a degree that at the present time they are to a considerable
degree comparable to the steam roads as regards speed.weight
of rolling equipment, and frequency of train movements. It
has, consequently, become necessary to signal them, and al-^
temating current track circuits and signals have come into
general use. On double track lines this has presented no dif-
ficulties and, as a matter of fact, the signaling equipment of
such roads is practically the same as on the steam roads and
electric trunk lines. Three-position semaphore or light sig-
nals controlled by polarized track or line circuits are usually
employed, and Fig. 197 will give the reader a good idea of the
standard layout.

However, most of the interurban roads are single track
lines and in signaling them new problems have been encoun-
tered. These problems arise chiefly from the fact that, while
the signaling must be such as to prevent opposing moves
through the block between twp sidings, it must, in case of
dense traffic, allow properly spticed following cars to proceed
through the block at the same time. Obviously, these re-
quirements will be met only by some scheme of signaling
wherein the relative direction of the moving cars will be
taken into account. To meet these exacting requireiyients
with safety and to facilitate train movements, the scheme of
automatic blocking known as tfie " T. D. B." system (Traffic
Direction Block) has been de^sed and extensively adopted.

THE T. D. B, SYSTEM.

1. General Description. The signaling layout is illus-
trated in Fig. 198. Two cars are permitted between sidings,
each in a separate block, and are protected head-on anct rear
by absolute signals. There is but one track circuit and four
signals for each opposing block iinit. The blocks for c^ppos-
ing cars do not coincide with the blocks for the following cars,
and hence the following definitioins will be useful.

OpposingBlod^s: The section of track from one siding to

ySl ALTERNATING CURRENT SIGNALING.

the next mding; so called because a car at any point bet%«reen
sidings will block opposing cars at the next siding.

Following Block* One-half of the section of track from one
nding to the next siding; so called because there are two
blocks for following cars in one block for opposing cars.

Each opposing block, extending from siding to siding, is
equipped with four signals, two of which are at the ends, or sid-
ings, and two (one for each direction) are near the center of the
block; these latter signals are known as intermediates. Each
signal at a siding governs to the signal at the next siding in the'
case of opposing movements, but only to the next signal in the
same direction of traffic in the case of following movements;
whereas the intermediate signals govern to the next signal
for the same direction of traffic — the signal at the siding.
*• Besides serving as automatic block signals for following
moves, the intermediates, spaced at sufficient braking dis-
tance apart, provide perfect head-on protection in case two
opposing cars should pass the signals at their respective ends
of the block at exactly the same instant, as of course with no
train in an opposing block the signals governing entrance
thereto are both clear.

Another way of securing similar protection is to provide
a short preliminary track circuit in advance of each oppos-
ing block, so that a car on this preliminary will throw the op-
posing signal at the next siding to danger, an opposing car
being held at this latter siding until the first car has proceeded
through the block. Thus, the control of the signal at one end
of a block is extended past the signal at the opposite end of
the block and into the adjoining block, so as to pirevent the
two opposing cars from entering the block simultaneously.
Unfortunately the preliminary section is always near a nding,
and as a result, a car standing within the Umits of the pre-
liminary may prevent an opposing car from entering the ad-
joining block, even though this block is clear and the car
should be allowed to proceed.

The absence of preliminary track circuits and the use of
intermediates, as illustrated in Fig. 198, makes opposing block
(from siding to siding) a unit; this allows very flexible oper-
ation, as cars which are to meet may advance promptly to the
sidings. Anothei advantage is that close headway is permit-
ted for fallowing cars, without complication of apparatut.

INTERURBAN ROAD SIGNALING.

353

2« Operation of the System. Figs. 198 and 199 show
the indications assumed by each signal as one or more cars
proceed through the blocks.

WUT

^^^^

r-^*

•ir—

..^

» «

^n^l^

,^r

Fig. 19d. Effect of Train Movements on Signal Indications in the T. D. B.

Sjrstem.

In Fig. 198 at A, a westbound car is approaching siding X,
and opposing signal 2 is at stop.

At B the car is passing signal 1 setting it at stop. Signal 2
is held at stop until the car has passed. Opposing signeJs 4
and 6 are also set at stop.

At C there is no change except that signal 2 has cleared as
the car has passed out of the block at the left.

At D the first car "R" has proceeded to signal 3, and a fol-
lowing car is approaching signal 1 . Signal 1 is protecting the
rear of car "R" and signals 4 and 6 protect it against opposing
movements.

At E car *'R", having passed signal 4, signal 1 has cleared
up for car **S."

At F car "S" has entered the first following block, while
car "R" is in the second following block. Opposing signals
4 and 6 still protect the cars against opposing movements,
and signals 1 and 3 protect against following movements.

At G car **R" has entered the next opposing block while
car "S" is following and both are protected rear and head-on.

The operation for east bound cars is similar.

At H, I, J, K, L, Fig. 199, are shown the positions of the
cars and the indication of signals as a meet is made at siding
Y. In this case one car heads in and backs out of the siding,
although this particular method of making a meet is not neces-
sary. ~ It will be evident that either car can take the siding

354 ALTERNATING CURRENT SIGNALING.

* ^^-^^"^^^^^^ ■ I Ml I 11 ■ I ■ — ■ I- - ■ I ■■ - — - I I ■— -I — — ^- — ■ ■ ■■ ■ ■ ■ ■ ■ ■ ^l^M^M^^M^^

because all sidings are shown double-ended, and this system
of signaling will permit either car to back in and head-out,

t ^^^ i WSST

^_JL* Q.» ^ _J—^'

f-^"

^W2^^ •^'''~' !°5^sr

Fig. 199. The Poeition of Cars and the Indicalions of the Signalf as a Meet

Made at a Siding.

head-in and head-out, or head in and back out. With stub
ended sidings and signals placed opposite the fouling or clear-
ance point of the sidings, the cars would be protected equally
well by the signals with this system, for a car on a siding does
not atfect any of the signals in any way.

It will be noted that cars between X and Y do not in any
way atfect the signals between Y and Z. This is shown at
M, N. O, P, Q. Fig. 199. At M, car ''R" does not atfect the
movement of car "T", which, we will assume is late. At N
and O, car '*R" is shown proceeding into the siding so as to
clear opposing block X to Y for car **T." At P and Q, an
east-bound car is taking siding without affecting the move-
ment of a west-bound car **U."

These diagrams cover all usual car movements. Special
movements of any kind are protected equally as well, as the
broad principle of track circuit control insures that, when the
track circuit, or block, is occupied, the signals will be in the
stop position, and when the track circuit or block is unoccu-
pied, the signals will be in the proceed position. No se-
quence of movements is required to secure complete protec-
tion. Therefore, cars may leave a block at any point, and the
signals will assume the proceed position.

INTERURBAN ROAD SIGNALING. 355

From the above description it will be evident that the sys-
tem possesses the following advantages:

1 . Each car is at all times protected in the rear as well as
head-on by one, or sometimes two, stop signals.

2. When the block is unoccupied and a proceed signal is
given, thq car may proceed through the block at full speed.
Hiis is an importeoit improvement over a circuit scheme where-
by following cars are given a caution or permissive indica-
tion to proceed through the block at reduced speed; in this
latter case, providing the train schedule is properly arranged,
the preceding car will have gotten out of. the block long before
the following car has had time to proceed very far into it and
hence the following car loses considerable time because it is
compelled to run through the block at slow speed.

ENGINEERING DETAILS OF THE T. D. B. SYSTEM.

3. Circuit Scheme. The complete circuit layout for one
block unit is shown in Fig. 200. The track circuits are of the
double rail t3rpe described in Chapter V, both rails being used
for the return of the propulsion current.

Each opposing block has one track circuit with two track
relays T1 and T6, track transformer R supplying current at
the center of the track circuit; it is through the employment
of this center fed track circuit that traffic direction control is
secured. Each track relay will be shunted by any car which
may be on the track circuit between the track relay itself and
the transformer feeding it. Both track relays will be shunt-
ed by a car within a short distance on each side of the trans-
former. There is, therefore, a territory on each side of the

transformer within which a car will shunt both relays.

Referring to Fig. 200, signals 1 and 6 normally are con-
trolled by both track relays or the entire section of track be-
tween them. Signal 3 is controlled over the points of line
relay 3L by track relay T6, and signal 4 is controlled over the
points of line relay 4L by track relay Tl .

A westbound car entering the block XY at X will de-
energize the track relay Tl , and thereby set signals 1 , 4 and 6
at stop. As signal 3 is controlled by the track relay T6, it
will not be set at stop until the car reaches the point near the
track transformer where it atfects relay T6.

3S6 ALTERNATING CURRENT SIGNALING.

INTEBURBAN ROAD SIGNALING.

The car, in de-energiziiig relays T I and 4L, eoeisize* (tick
relay 3S which is used to clear signal I after a car has passed
signal 4. This stick relay cuts out the control of signal I from
the track relay T6 and line relay 3L. As the car prcKeeds,
passing signal 3, track relay T6 is de-energized, setting signal
3 at stop and still holding the other three signals at stop
When the car passes signal 4, track relay T I is again ener-

Fif. 201. Complete Power Houn Equipoent [

gized and signal I is cleared. Incidentally, signal 4 is cleared
because track relay Tl is energized, but this has no effect on
westbound movements. When the car has passed signal 6,
all signals and relays again assume their normal pontkma un-

356 ALTERNATING CURRENT SIGNALING.

less a second car has entered the block at signal 1 before the
first car passed signal 6. The operation of east bound cars
is similar.

Stick relay 3S is active only in connection with westbound
movements; eastbound movements have no effect upon it.
Therefore, an eastbound car will set signal 1 at stop when sig-
nal 6 is passed. Likewise stick relay 4S is used to limit the
control of signal 6 in a similar manner for eastbound move-
ments.

It will be noted that the circuits are so arranged that but
one of the two stick relays 3S or 4S can be energized at any
one time. Evidently, if a westbound car should pass signal
1 at the same time that an eastbound car passed signal 6, sig-
nals 3 and 4, being directly controlled by the track relays,
would afford positive protection.

From the foregoing description the system may appear to
require a certain sequence of car movements, but this is not
the case. A westbound car could proceed past signal 1 and
afterward back out of this block instead of proceeding through,
and all apparatus would again become normal when the car
had left the block. The same would happen if an eastbound
car should enter at signal 6, and then back out. The ar-
rangeihent of circuits in conjunction with a standard relay
so that it will be active for one direction of traffic only is not
novel, not does it involve complication of apparatus or cir-
cuits.

4. Types of Signals Used. Either semaphore or light
signals may be used throughout, but semaphore signals are
more generally employed at sidings for the following reasons:

First. They provide indications which can be clearly seen
while making movements into and out of sidings; therefore.

Second. They render unnecessary the use of switch indi-
cators at adjacent switches.

Third. They are of the same general type and give the
same indications as signals which have been standard in steam
road practice for many years.

Fourth. They have a much greater advertising value, for
their operation may be easily observed by passengers and the
general public.

5. Power House Equipment. Hie signal system is
generally fed from 2200 volt single-phase mains receiving

INTERURBAN ROAD SICNALINC 3M

power from a atep-up tranafoimer located in a convenieiit
power tiouae or sub-Btatioii. Duplicate ttep-up transformers
are always provided to guard against a tie-up in case of light-
ning trouble. The neccusary switching is accomplished by
means of a simple switdibooid such at that illustrated in Rg.

rit.202. Styl«"B"SigiMj.Mitib«Cliic««o.L.keSlw.«&SouthBendRy,

201. «4uch photograph also shows the duplicate transfoimers
above mentitsied. The reader is referred to Figs. 194 and
195^ {Chapter IX) and the explanation given in connection
therewith for a full descriptitai'Vnd circuit* for a standard

MO ALTERNATING CURRENT SICNAL.INa

«w>tchbo»rd for use in connecticoi with inteniTban signaling.

S. Examples. The following concrete examples of in-
■tallBticata nude on the roads listed below will perhaps serve
to better illustrate the T. D. B. system:

Miles. Blocks.

Chicago. Lake Shore ft South Bend Ky 55 20

Indianapolis, Columbus & Southern Tract. Co. 22 13

Chlcaeo. South Bead ft Northern Indiana By. 9.5 6

LoulsvlllE & Northern Rf. & LigbtiDg Co 3.G 2

Ohio Electric BaUway 4,2 2

Scranton &: Blngbampton Bailroad 16. 1 19

Kansas City Clay Co. & St. Joseph By TO. 1 25

In this table the blocks constitute the territory from siding
to siding.

On these lines
the semaphore
signals are of the
Style B type,
electrically
lighted, two-po-
sition, working
in the upper left
hand quadrant.
as shown in Fig.
202. They are
equipped with
induction
motors and the
mechanisnu are
at the bottom of
the posts. On
.h. Chi„go, ^ ^^j
Lake Shore &
Southern Bend,
and the Chicago. South Bend & Northern Indiana, all signal*
are semaphorea. On the other roads light signals are used
as intermediates. These light signals are of the Modd 13
type (Fig. 203), equipped with two 8" lenses each. They
carry hoods to screen the lenses from sunlight and back-
ground* to increase the visibility. Behind each lens ore two

INTCRURBAN ROAD SIGNAUNa

25 wall 16 C. p. tungsten Umpe. See Chapter VIII, Part II.
for a full discussion of the various types of light signals and
their application.

Eai^ block — siding to siding — ^has but one track a

362 ALTERNATING CURRENT SICNALING.

with a track relay at each end. Current is supplied by trans-
formers at the center of each block. Galvanometer track re-
lays (see Chapter IV.) are used on the six D. C. propulsion
roads, and centrifugal frequency relays on the Chicago, Lake
Shore & South Bend, which operates on alternating propulsion
current at 6600 volts, 23 cycles. The semaphore signals are
directly controlled by the track relays, whereas the light sig-
nals on the Indianapolis, Columbus & Southern Traction,
Louisville & Northern Railway & Lightning, Scran ton & Bing-
hamton, Kansas City, Clay County & St. Joseph, and the
Ohio Electric, require line relays which operate on 1 10 volt
circuits controlled by the track relays.

All signal apparatus is designed for 60 cycle operation, ex-
cept on the Scranton & Binghamton, the Ohio Electric Rail-
way and the Kansas City, Clay County & St. Joseph, where
25 cycle current is used. The signal slot coils are controlled by
line wire circuits through the track relay contacts, whereas the
signal motor circuits receive their current from transformers
at the sidings. They are on purely local circuits. Trans-
formers with two secondaries, one for the track circuits and
one to deliver 1 1 0 volts, supply current at the center of the
block for the track and to line and intermediate signal cir-
cuits. Other transformers with one 1 1 0 volt secondary each,
placed at the turnouts, supply current for the siding sema-
phore signals cuid line circuits. These transformers are pro-
vided with taps as required, and all receive current from the
2200 volts A. C. mains.

'The Indianapolis, Columbus & Southern Traction, the Chi-
cago, South Bend & Northern Indieoia, the Louisville &
Northern Railway & Lighting, the Scranton & Binghamton,
the Ohio Electric and the Keoisas City, Clay County & St.
Joseph are D. C. propulsion roads. On the first six the po-
tential is 600 volts, on the last 1 ,200, and the impedance bonds
have a capacity of 500 amperes per rail. The impedance bonds
on the Chicago, Lake Shore & South Bend, where alternating
current at 6600 volts is used, have a capacity of 200 amperes
per rail. Circuit controllers connected to the switch points
require the switches to be set for the main line before the sig-
nals at the sidings can assume the clear position. All relay
boxes are of iron, mounted either on separate iron posts or on
the semaphore signal

INTERURBAN ROAD SIGNALING. 363

Fif. 20}. Three PeeidoD Model 13 Li|Eit KgruU. PkciCc Electric Ry.

CHAPTER XI.

TYPE **F"
A. C. ELECTRIC INTERLOCKING,

366 ALTERNATING CURRENT SIGNALING.

CHAPTER XI
TYPE "F" A. C. INTERLOCKING.

1. General. Considering the high degree of perfection
which alternating current motors and other devices have
reached, not only in signal work but also in the industrial
field, there seems to be no reason why such appai'atus should
not with advantage be employed in an interlocking system.
Already in many interlockings within A. C. automatic terri-
tory, the track circuits and such signals as are automatic or
semi-automatic in character are frequently arranged for oper-
ation on alternating current in order to maintain the con-
tinuity of the block system. It is only a logical step to oper-
ate the signals likewise. Wherever there is a reliable source
of alternating current power available, an A. C. electric in-
terlocking will possess the following advantages:

1. The power equipment is greatly simplified since
the storage batteries, rectifier, and accompanjdng switch-
board generally used in D. C. electric interlockings are
eliminated in favor of a simple transformer, low in first
cost and requiring no maintenance.

2. The efficiency of the transformer will run between
96 per cent, and 97 per cent. In a D. C. electric inter-
locking the storage battery will return only from 40 per
cent, to 60 per cent, of the energy put into it; if a rectifier
is used for charging a further loss of energy occurs in the
rectifier itself whose efficiency is 75 per cent.

3. In point of safety and economy the alternating
current track circuit is unequaled as it is free from for-
eign direct current influences. Such track ciiTcuits, used
for detector locking and the semi-automatic control of
signals, become immediately available in an A. C. elec-
tric interlocking system.

Suqh are the apparent advantages of any A. C. electric in-
terlocking. The type "F" system, the invention of Mr. W. F.
FoUett, Assistant Elngineer of Signals of the N. Y., N. H. &
H« R. R., and assigned to this company, possesses certain
other important advantages, however, which make it par-
ticularly attractive in safe, economical and reliable operation
on either alternating or direct current, and the reader who is

368 ALTERNATING CURRENT SIGNALINa

«— . , ,

interested in the details of the D. C. interioddng is respect-
fully referred to our Bulletin No 7 1 . The system is based on
one simple principle, viz., the feeding of all functions from a
pair of bus mains extending the length of the interlocking,
power being admitted from the mains to each function, over
the contacts of a local relay controlled from the machine m
the tower; the bus mains correspond to the main air line in
the well-known electro-pneumatic interlocking system, and
the control relays to the valve magnets. Naturally this re-
sults in an enormous saving in copper since the control wires
for the loc€d relays need only be large enough to stand up
mechanically, whereas if the functions were fed directly from
the tower, each set of wires would have to be large enough to
carry the entire operating current. Further advantages in
simplicity and safety are secured through an ingenious indi-*
cation scheme which will presently be described.

2. Elements of the System. The type **F*' alternating
current interlocking consists of:

(a) A transformer, generally in duplicate, for step-
ping down from the transmission voltage to 1 1 0 volts for
the interlocking bus-mains; the source of power may be
of any voltage or frequency.

(b) Two bus -mains for delivering current to the signals,
switches, etc., to be operated.

(d) Motor operated switch and lock movements for
moving and locking the switches.

(e) Motor operated signals for governing train move-
ments over the tracks after the switches have been
lined up.

(f) Auxiliary devices, such as tower indicators, time
releases, etc., now so generally used in interlocking work.

MAIN TRANSFORMER.

3. Size and Location. The size of the main transformer
for feeding the bus-mains will naturally depend on the number
of functions to be operated. In calculating the size, however,
it is well to remember that the load constituted by the switch

TYPE "F* A. C. m-€CTRIC INTERLOCKING^ 369

and signal motors is only momentary in character and any
well-designed oil-cooled transformer is capable of withstand-
ing a 73 per cent, overload for the few seconds taken for
switch or signal motor operation. As examples, the writer
has in mind two type "F" A. C. interlockings of the follow-
ing sizes:

Interlocking A.

10 levers for 13 switches, 2 M. P. frogs and 3 derails.
13 levers for 20 signals.

23 working levers.
1 0 spare spaces.
33 lever machine.

Interlocking B.

9 levers for 16 switches and 2 derails.
1 3 levers for 26 signals.

24 working levers.
3 spare spaces.

29 lever machine.

For each of the above layouts a 1}4 K. V. A. transformer
was found adequate, and the cost of the combined power for
both of them, including track circuits for semi-automatic
control and detector locking, as well as that for the operation
of 13 top arm automatic blades on interlocked signals, ran
about $1.73 per day at the rate of 2} cents- per kilowatt-
hour.

4. Location of Main Transformer. The transformer
ought to be located at the load center, or "center of gravity"
so to speak, of the bus-mains; this is the point on either side of
which the sums of the products of the current taken by each
function times the distance of the function from the load cen-
ter are equal. In the case of switch movements, the current
will be about 6.0 amperes per point, and the signal motors will
take between 2.2 and 3.3 amperes, depending on the type of
mechanism employed. Maximum copper economy in the
mains is secured when the transformer is so located, as will be
evident after a moment's reflection; for example, if the trans-
former were placed considerably to the right of the load cen-
ter, the mains to the left would have to be correspondingly
larger if the drop were to be kept within the proper limits.

370 ALTERNATING CURRENT SIGNALINa

THE INTERLOCKING MACHINE.

S. Part* and their Functions. The type "F" inter-
locking machine illuBtrated in Pieb. 206, 207 and 208, is a <Ie-
velopmcDt of the well-known electro-pneumatic machine. It
consists of miniature levers conveniently arranged in a com-
mon frame and adapted to the operation of a bank of mechan-
ical locking, but of diminutive design. Each lever in th«
machine also operates the necessaiy electric contacts, and
attached to each lever are one or more dectric locks.

The mechanical lacking is provided for prevailing the oper-
ation of levera which, i( moved, would conflict in function with
one or more other levers.

The lever amfacU ccmtrc^ electric currents for the opera-
tion of the local relays at awitchea and signala, and ore also
used for opening and closing different circuits as required by
the many combinations of lever positions.

The eiectric bd^s are provided for restraining lever opera-
tion according to conditions remote from the machine when
these are adverse to their safe operation, such aa preventing
final movement of levers until the operated unit has responded
to the initial lever movement and preventing the initial mov^
ment of switch leveia 1^ train action where detectcnr tra^

TYPE "F" A. C. ELECTRIC INTERLOCKING. 371

circuits are used instead of mechanical detector bars.

It is the custom in the type '*F" system to operate from a
single switch lever all of the switches upon the ground which it
is permissible so to operate without restricting simultaneous
traffic movements, and irrespective of the loads thus produced
upon any lever. In the case of signal levers, it is the custom
to operate all signals which under all circumstances govern
routes conflicting with each other; thus many signals leading
from individual tracks to a common point and diverging from
the common point are handled from the same lever.

The form of lever used and the manner of its op>eration
were adopted years ago to obtain, etfectively, the concentra-
tion of many levers within the smallest space practicable. This
form was adopted to insure that the operation of many
switches and signals from a central point might be ejected
without frequent shifting of position by levermen during lever
manipulation and without extravagance in the dimensions
of the structure containing the machine. The general testi-
mony of levermen is that with side throw levers as used in the
T3rpe **F" machine, a less number of men are required per
trick than would be the case with a machine where the levers
must be pulled directly outward, for if cm attempt is made to
throw levers of this latter type from the side, binding due to
side friction results; hence the leverman must shift his posi-
tion each time so that he may be directly in front of the lever
to be pulled. T3rpe **F** levers on the contrary may be thrown
from any position within the leverman 's reach.

Due to this form of lever construction, a large machine may
often be operated by a single leverman while its location con-
veniendy within the track system involves no serious en-
croachment upon space usually much needed for track pur-
poses. The device is self-contained and suitably encased in
a wood or metal case provided with detachable panels, each
provided with means for locking the machine against access
by other than authorized persons.

The type "F" machine is a development of the well-known
electro-pneumatic machine, and few, if any, devices in ex-
istence to-day that were designed for the safe and reliable
control of a multiplicity of contacts embrace that degree of
concentration, security of construction, current carrying ca-
pacityf in^ulfktion and el^Qtrical sepe^ration of current carrying

372 ALTERNATING CURRENT SIGNALING.

Fif. 208. SkiidhI Kde View Type "F" InlerlccklnE Machine.

TYPE "F' A. C. ELECTRIC INTERLOCKING. 373

porta with that degree of acceaaibiUty and eaae of inapectum
that are conapicuoua features of the electrical equipment of
the type "F" machine. Thirty years of development have
not only permitted the embodiment within this machine of
these characteristics, but have also made possible the ma-
chine's application to the operation of track layouts of ex-
treme magnitude, and the direction of traffic of the most con-
gested nature, without the slightest modificBtione of its struc-
ture or resort to aubstitule appliances for meeting the intrica-
cies of special control and operation that such application*
frequently have to provide for.

6. Lever Movements. The complete operation and
locking of a switch (from either of its two positions) is effected
in this sjistem, as in all power
interlocking systems, by a par-
tial (preliminary) movement of
its lever, the complete (final)
movement of the lever being
impossible until the proper
response of the switch to the pre-
liminary lever movement occurs.
Two systems of circuits are em-
ployed for these purpoeesi one
for effecting switch operation,
and one for releasing the lever
thereafter for its final move-
ment, the latter involving what

is known as the Indicallan —b™-™..,

system. The complete opera- _ "■~-^*~ """""•----■
. , . 1 , Fit- 209. Dugrmm of Lock

tion of a signal from stop to Mogwl imd it* Sesmeot.

proceed is effected by a con-
tinuous complete lever movement, but its operation from
proceed to stop necessitates two movements of the lever; a
preliminary movement for interrupting the power sup|Jy to
the signal, and a final movement that can be made only
when the signal, so deprived of power, returns fully to the
stop position. The operation of switches and signals thus
involves the opening and closing of electric contacts during
lever movement and at definite points in the lever's throw.
IIm control of lever movement by switch and signal position

374 ALTERNATING CURRENT SIGNAUNG.

(which alio embraces this contact contnid) necessitates the
use of electric locks (Fig. 200) upon the machine which
permit or prereait lever operation! according to the ener-
gized or de-energized state of their magnets. Contrtd of
these locks is not restricted solely to switch and signal
operation, train acticoi being also at rimes a factor in it.

Fig. 2tOa represents the several posirions occupied by a
•witchleverAtimportant times during the operation of a switch

(»J

(a)

mtinc dw OpcrKtion of Switch L«v«n.

from Normal to Reverse and from Reverse to Normal. It
also shows the formation of the quadrant secured to the front
of the machine frame and that of the lever latch carried by
the lever, aa theiie are designed to restrict lever movements un-
der certain conditions. 1 1 also illustrates means for forcing the
kver-latch into engagcmoit with the quadrant at midstroke:
« meaiM provided that this quadrant and not the segm&t*

TYPE "F" A. C. ELECTRIC INTERLOCiqNa 375

of the «lectric locks will receive the impact of the lever't ar-
rested movement, thus insuring entire freedom of action of
ihe latches of the electric locks when these are to be elevated
to release the segment, for final lever movement after the in-
dication is received. Incorporated also in thia figure, but
only in a vague way shown, is a stud or pin which co-acts with
the latch to open and to maintain open a set of contacts under
certain positions of the latch and the lever; this circuit con-

Fif. 211. Ducnm Illuatntini ibc OpeiitiDn of ScmI Levsn.

troUer, and its operation jointly by the lever and the latch;
will be described in connection with the automatic locking
of switch levers by train action through the medium of the elec-
tric locks, employed primarily for switch indications. Fig. 2 lOb
represents one of the two segments and latches of a switch
lever that are employed Jointly for switch indication and d^
tector circuit locking. Hg. 210c shows diagrammatiolly thf

376 ALTERNATING CURRENT SIGNAUNG.

several positions occupied by a switch lever, as already re-
ferred to, and the angle of rotation that lever movements im-
part to the contact rollers of the machine during lever opera-
don. These rollers move at double the speed of the levers
and, hence, their total angular movement is double that of
the levers, or 120 degrees. Fig. 210d shows a section of the
hard rubber roller that, while mounted concentrically upon
aud operated by the roller shaft, is not continuously movable
with the shaft, but is restrsdned from following it during pre-
liminary lever movements by a spring actuated toggle and
until the final movement of the lever occurs after the indica-
tion has been received. This device is embraced in the in-
dicating system and is known as the "quick switch.*'

Fig. 21 1 shows like characteristics of the Type "P* signal
lever. Fig. 212 shows, in perspective, the actual design and
relations of the various features of the switch lever, while
Fig. 213 shows in like manner those of Type **F**
signal lever. Fig. 214 shows a frsigmental view of the in-
sulated plate which carries the contacting system of the ma-
chine. This drawing also illustrates certain features of con-
struction peculiar to the rubber rollers, quick switches, and
contacting devices that will be referred to elsewhere.

7. Checks on Lever Movements. In describing the
operation of the levers of the type "F" machine, the efiFects of
lever movements upon switch and signal position, and the
efiFect of switch, signal and train operation upon lever manipu-
lation, it is assumed that the function of the mechanical lock-
ing of the machine is fully understood to be: first, the release
of one lever for operation only after another has been fully
operated; and, second, the locking of one lever sigainst opera-
tion by movement of another lever before movements of the
other have advanced sufHciently to afiFect those conditions
which prevailed before an attempt to move it was made. No
detailed description of this feature of the machine will be
given, because the type of locking used is well understood and
its efHciency and durability are well known to everyone at all
familiar with mechanical interlocking practice. In die meth-
od of driving the bars of this locking from the levers in the
type "F" machine, a departure from the practice employed in
mechanical interlocking machines was made, however; this

TYPE "F" A. C. ELECTRIC INTERLOCKING. 377

Fl|. 212 '^enpKtive Diagiun of Switch Lever CompleM.

ALTERNATING CURRENT SIGNAUNG.

Fif' 213- Panpectivv DiAgrani ot Signal Lvvn ComplatB.

TYPE *T" A. C. ELECTRIC INTERLOCICING. 37^

embraced not only a much more direct and a simpler driving
mechanism than that there used, but it involved the opera-
tion of the locking during lever movements, and not prelim-
inary to lever movements, as in its operation from the catch
rods of mechanical machines. This method was employed
both because of its great simplicity and because in power in-
terlocking practice, levers are necessarily moved through a
considerable part of their stroke before their movement is in*
fluential in causing switch or signal action. This fact com-
pletely removes from all power interlocking machines that
need for a preliminary operation of the mechanical locking that
arose in mechanical interlocking through the fact that a
change of switch and of signal position is there simultaneous
and continuous with lever operation. There is, however, an-
other feature embracing the locking of levers (both electri-
cally and mechanically) that is involved in the concentration
6f this feature of the catch-rod's function within the lever
itself, which should be made clear before the foregoing state-
ment can be accepted as in all respects true. The movement
of the switch lever. Fig. 210a, to position D is the first act
necessary to operate the switch. This movement is possible
only when the switch lever is unrestrained by both the me-
chanical and the electric locking of the machine. Ordinarily,
the mechanical locking prevents any appreciable movement
of the lever from position N when restraining the lever's move-
ment. When the mechanical locking of one lever by another,
however, is dependent upon the positions assumed at the
time by memy other levers (as is often necessary) it is imprac-
ticable to lock the lever so securely as to prevent a slight
movement of it being made when mechanically locked. In
consequence of this, it is of impK>rtance that the electric locks
should be so designed as to engage the lever in any position
which it may occupy while restrained from effective move-
ments by the mechanical locking. To this end, the electric
lock, while preventing effective lever movements, still per-
mits of a partial movement of the lever from either of its ex-
treme positions (from N to A or from R to E). This partial
movement is without influence upon the system of contacts
dperated by the lever and hence may be totally ignored as an
element essential to switch operation — ^its function being sim-
ply to provide after the effective operation of each lever has

380 ALTERNATING CURRENT SIGNALING.

occurred, a further excess movement to permit, by that excess,
the mecheoiical and the electric locking of the lever in a
wholly safe manner and without resorting to the complica-
tion peculiar to preliminary locking.

Preliminary locking by lever catch-rods is indispensable to
safe lever operation and control only when the lever itself
is not given this excess of stroke, or when this excess of stroke
is not employed exclusively for the function assigned, in me-
chanical interlocking practice, to lever catch-rods. When
levers are given this extra throw, the catch-rod or lever-latch
becomes simply a means for restraining the lever in one or the
other of its extreme positions against inadvertent operation
at times when lever operation is unrestrained by the lock-
ing. Those positions of the switch lever represented by lines
A and E, Fig. 2 1 0, may, therefore, be regarded as correspond-
ing with what would be the extreme positions of the lever were
the catch-rods employed for preliminary locking purposes, as
in mechanical interlocking practice, and were the electric
locks applied to the catch-rods and not to the levers. The
line D represents the position to which the lever is moved
continuously from N, to effect the change of switch position.
Beyond this position the lever cannot be moved until the
switch, in response to the lever movement, completes its oper-
ation and thereby energizes that one of the indication magnets
which, through its depressed latch, restricted the lever's move-
ment at position D. Line B represents the indicating posi'
tion of the lever upon its return operation from R to restore
the switch to its original (normal) position, in which position
it is restrained by the other indication magnet until that mag-
net is energized by the responding switch.

8. Contact System. While it is customary to arrange
the switch levers so that these project upwards from their
shafts, and to arrange the signal levers so that they project
downwards, this is entirely an arbitrary matter. In practi-
cally all installations the number of switch levers required ex-
ceeds the number of signal levers required — ^largely by reason
of that dual capacity of signal levers just referred to — and it
not infrequently happens that switch levers are substituted
for signal levers in such cases. It, furthermore, sometimes
occurs that the requirements of certain levers in the way of

TYPE "F" A. C. ELECTRIC INTERLOCKING. Ml

contact equipment^ exceed the capacities of the two oectionaJ.'
ized rubber rollers ofeach lever that this equipment embraces.
1 1 invariably happens, also, in such cases that a single sectian
only of other levers is more than ample for meeting their needs
in this respect. To give to the former levers the desired ca'
pacities. the lower sections of the rollers of tlie latter are dis-
engaged from their upper sections and connected by links to
the overburdened rollers of the former levers so as to operate
with them. In this way, an almost unlimited capacity for
circuit control is assured each lever of the machine, and where
unusual conditions assign to the lever the control of many
circuits, DO complications of design or resort to special equip-
ment to meet its need is invcdved.

Fif. 2L4. Secdon of CombiutiDB Plate. RoIIen ud CunUcu.

The vertical arrangement of the rollers has two distinct ad'
vantages; first, in permitting of their operation through an
angle of 1 20 degrees— or double the angular throw of the
levers; and second, a concentration of the elements of the ma-
chine in the interest of the floor space occupied. TTie 120
degree operation of rollers is of especial value in obtaining, by
means of rollers of small diameter, a wide reparation of cmt-

3A2 ALTERNATING CURRENT SIGNALING.

tacts and a close definition of contact control with respect to
lever positions, thus insuring permanency of adjustments and
entire freedom from extreme care and delicacy in producing
it originally and maintaining it afterwards. The panels or
"plates" which support the contacting system of this machine
are of special moulded insulated material so formed and se-
cured to the machine frame as to prevent distortion due to
temperature or humidity changes. To these plates the con-
tacting springs are secured by substantial brass screws which
pass entirely through them and into square brass nuts of lib-
eral lengths by which the screw and spring are thoroughly se-
cured. These nuts, being square and set into vertical grooves,
cut in the rear of the plate, are non-turning, while the contact
springs lying in similar grooves cut in the front of the plate
are likewise held against tum»g by a single screw through
each. The nut by which the sci^^ew is secured is of extra
length where wire connection to a contact spring is to be made,
and that portion of the nut which extends beyond the screw
is equipped with a second screw i|nd washer for securing the
external wire connection. Over the terminal posts* thus
formed, a tube of insulating material is placed; the external
wire connection being in a notch cut in the outer end of this
tube, and when the wire is secured to the post by the screw
a very simple and effective means of retaining the tube is thus
obtained and a highly satisfactory protection afforded the ter-
minals of the machine against accidental crosses or grounds
during inspection, etc.; see Fig. 214.

The vertical mounting of the rubber roller might involve
some risk of badly fitted contact bands thereon slipping out
of position with serious consequences were means not em-
ployed for preventing it. To prevent this occurrence,
grooves are turned in the rollers, and the contact bands being
placed immediately over them are held against movement
longitudinally upon the roller by several lugs or projections
that are deflected into the groove after the band is applied.
The ends of the bands are turned at right angles and inserted
in two of the severally radially cut slots in the face of the
rollers to secure their rotation at all times with the roller.
These beoids vary in length and in their positions on the
rollers to meet the requirements of the circuit including them,

the matter of lever positions.*^ An electrical separation of

TYPE "F" A. C. ELECTRIC INTERLOCKING. 383

^£" is obtained between contacting members, terminal posts,
magnets, the frame of the machine throughout its con-
struction complying fully with R. S. A. specifications in this
respect and adapting the machine to safe operation with any
working e. m. f. from 12 to 250 volts. The 3000 volt A. C.
insulation test required by the R. S. A. is an important fea-
ture of the machine's construction, and a 5000 volt test is en-
tirely practicable where required, without mechanical modi-
fication of any sort. The electro-magnets used for locking
and indicating purposes are of the solenoid type and remain
upon open circuit practically 90 per cent, of the time.

9. Auxiliary Deviceft. The front plate of the machine is
constructed to recede from the place in which the levers operate
and thus to form a compartment under the levers for the housing
of the various lamps and contacting devices (see Fig. 208) that
are frequendy made a feature of lever manipulation in this
system. The lamps s^rve as indicators and inform the oper-
ator when a lever may or may not be used. The usual con-
tacting mechanism that is contained in this compartment has
several functions; first, the control of switch lever locks by the
catch-rods of the levers so as normally to retain the locks upon
open circuit, as a mattef of current economy solely; and, sec-
ond, the retention of these locks positively separated, during
lever movements between indicating positions from any pos-
sible supply of current energy to them save through the
proper channels of thd indicating system alone. Upon the
efficiency of this provision hinges to some extent the desir-
ability of the adaptation of the indicating magnets (alterna-
tively) to the duty of detector circuit locking. The
highly efficient and substantial manner of operating this con-
tacting device joindy by both the catch-rod and the lever, and
the joint control of the automatic lock circuit by this device,
and by certain roller contacts of the machine that, because
of the 1 20 degree angle 6f roller operation, are simple and cer-
tain of action, leaves no room for doubt as to the wisdom of
utilizing the indicating magnets for detector circuit locking
also. The third function of this equipment embraces, be-
hind each signal lever, when desired, a "latching" push-
button, the action of which, when depressed, is to operate
a "calUng-on" arm when the usual signal does not respond

384 ALTERNATING CURRENT SIGNALING.

to the lever's movement by reason of semi-automatic con-
trol of the signal and the presence of a train upon the track it
governs. The depression of the button, in such cases, me-
chanically latches it depressed, and, in consequence, the cir-
cuit of the calling-on arm is closed until the latch is released.
This release occurs by the partial restoration of the signal
lever to normal; i. e., its movement to interrupt the circuit of
the signal and thus to cause it to assume the stop position
and, thereby, the lever's release for final movement to nor-
mal, as in ordinary signal operation.

SWITCH OPERATION.

10. Operating Mechanism. Switches in the t3rpe "F"
interlocking, as in all well designed interlockings, are un-
locked, operated, and again locked by one continuous oper-
ation of the prime mover, in this case a motor housed in the
switch operating mechanism. This device is termed a SWitch
and Lock Movement, the general design of which is illustrated
in Figs. 215, 216 and 217.

Motor. The motor shown at the rear of the case in Fig.
216 works on exactly the same principle and has many of
the characteristics of the ordinary series motor used in D. C.
signal operation, which it will be remembered does not change
its direction of rotation when the current through both field
and armature is reversed simultaneously; hence, any D. C.
series motor will develop a unidirectional torque when con-
nected across A. C. mains. However, if a D. C. motor is to be
thus used, its field and armature coils must be well laminat^jed
in order to avoid heavy eddy current losses. Furthermore,
due to the cyclic variation of the alternating field Hux an
e. m. f. will be induced in each armature coil over and above
the counter e. m. f. of rotation, and. as the commutator seg-
ments connected to the terminals of the coil pass under the
brushes, a heavy short circuit current will flow and destruc-
tive sparking will result unless some provision is made in de-
sign to avoid it. The course followed in the present case is
to make the field magnetization weak so that only a very
small alternating e. m. f . is induced in the armature, the latter
being made of correspondingly stronger magnetization to se-
cure the necessary torque; As in the case of the D. C. series

TYPE "F- A. C. ELECTRIC ]NTERLOCKINC.

L C Electric Switch

ALTERNATING CURRENT SIGNAUNG.

Fi|.ZI6. Ma<Jcll3A.C.DKtricSwiichM<nn

. All Q>v«F> RBmovnl

TYPE "F" A. C. ELECTRIC INTERLOCKING. 3d7

^^^^— ^fc— » ■ ■ ■ ■ ■ ■■■ ■ ■ ■■■■-■ III. 1 ■>

motor, however, this armature flux exerts a demagnetizing
action on the main fldid flux, and as the latter has to be made
weak to avoid sparkling, it is necessary to employ a so-called
compensating winding to balance the armature reaction. This
compensating winding, clearly shown in Fig. 219 is distributed
in slots in the field core and is short-circuited on itself in such
a manner that the current induced in it by the main field sets
up a magnetization practically neutralizing that component
of the armature magnetization which opposes the main field.
Such a motor is known as a Compensated Series motor.

The armature is reversed to throw the switch points from
one position to the other by reversing the direction of the
current in the main field coil relative to that flowing in the
armature, this latter element remaining fixed. ' The motor is
designed to unlock, throw over and again lock the switch
points in 2.3 seconds. Furthermore, like the D. C. series
motor, the A. C. compensated series motor here described
has an enormous overload capacity since, as it slows down
as load increases as would occur if the switch points were
frozen or blocked with snow, the armature counter e. m. f.
falls off, more current flows, and the torque increases corres-
fK>ndingly.

Gear Train and Slide Bar. The motor carries at its
right hemd end in Fig. 216 a pinion, which, through the me-
dium of a simple cone friction clutch, drives the gear train
housed at the right of the motor in the above photograph.
The last pinion of the gear train engages with a heavy toothed
rack milled into the slide bar which, riding on substantial
anti-friction guides, carries a stud engaging an alligator jaw
or escapement crank connected direcdy to the switch oper-
ating rod projecting sidewise to the right of the case in Fig.
216. The operating rod is shown connected in Fig. 213, as
is also the lock rod, this being the rod nearest the observer;
the lock rod may be made adjustable or solid as may be re-
quired, but in all cases the whole locking arrangement may
be easily gotten at or inspected since the cover of the shallow
lock box can be removed in a few seconds. Where a detector
bar is required, an operating rod, projecting longitudinally
out of the case in Fig. 216, is provided.

366 ALTERNATING CURRENT SIGNALING.

Switch Circuit Controller. This device, illustrated at
the extreme lower left hand comer of Fig. 216. and in detail
in Fig. 218. is the polarized cimtrol relay, operated from the
machine in the tower, over whose contacts the direction of
current flowing in the main field of the switch motor is re-
versed to throw the switch points one way or the other as
required. The controller is very simple in construction, con-
sisting of a bipolar laminated field magnet carrying a cchI the
direction of current through wliich ia controlled from the

Fig. 2IS. PoUriied Switcb Circuit Cantrolleia.

switch lever in the interlocking machine. In the bore of the
fidd magnet swings a shuttle or armature whose extended
shaft carries the movable contacts sho^vn in Fig. 218; pro-
jecting out from the front of the motor frame to the left
are two blocks of moulded insulation to which are at-
tached flexible contact springs and their terminals. The
armature is permanently connected to the bus-mains and is
hence of constant polarity in relation to the field; when the
switch lever in the tower ia reversed, it reverses the polarity

TYPE "F" A. C. EL£CTRtC IMTERLOCKlINCi. ^M

of the field in relation to the armature, and the latter imme-
diately shifts, the contacts which it carries then reversing the
motor. The armature torque is made intentionally large to
insure good contact pressure and its shaft is provided with a
simple toggle spring device which latches the contacts
closed against train vibration, and they remain firmly closed
until the armature is again reversed. Both elements of the
switch circuit controller are thus continuously energized but
the actual power taken in watts is very small due to the highly
inductive character of the windings; in other words, the de-
vice operates on an extremely low power factor.

Indication Circuit Controller and Transformer. This
controller, whose terminals and contact springs are seen im-
mediately next the motor in Fig. 2 1 6, consists of a cast iron
frame carrying a contact operating shaft driven from a cam
connected direct to the main gear train. To the top of the
frame is attached a block of moulded insulation supporting
stationary contact springs and their terminals. One set of
these springs serves to open the motor circuit after the switch
has been thrown and locked, as will be evident from a study
of the circuits shown in Fig. 219.

The controller is, however, provided with a set of pole-
changer springs and between it and the switch circuit con-
troller previously described is a small transformer, whose pri-
mary is directly attached to the bus-mains. The secondary
of this transformer feeds current at 11 0 volts over the pole-
changer contacts of the indication circuit controller acting as
a pole-changer to a three-position relay of the polyphase type
(Fig. 221 ) as described in Chapter IV; one set of contacts of
this relay energize the normal indication magnet on the
switch lever and the other set control the reverse indication
magnet. The pole-changing contacts of the indication cir-
cuit controller are so designed that when the switch is in tran-
sit or is not fully locked at normal or reverse, the two wires
leading to the three-position indication relay in the tower
will be short-circuited and the relay will hence not only be
de-energized but will be absolutely short-circuited. The pro-
tection against crosses and false indications, secured not only
by this short circuiting feature, but more especially by the
polarized character of the indication system, and its entire

390 ALTERNATING CURRENT SlGNALrNG.

Rl. 219. Complete Op«ntinEUidln(lSctt!finCin;uit* for uSinile!

TYPE "F" A. C. ELECTRIC INTERLOCKING.

391

isolation from the bus-mains, will be more evident from a study
of the circuits in Fig. 219.

To
lAfO/CAr/OAf

■o ■■■•- I ■«

I r/fANSrOPM£/f — ^^ -^

Fig. 220. Indication Circuits for a Crossover and for a^Sst of Movable

Point Frogs.

11. Circuits for Switch Operation and Indication.
Referring to Fig. 219, the significance of whose lever contact
symbols is given on page 512, it will be noted that the switch
lever is shown in the full normal position at which time the
two lever contacts NB, serving as jjole-changers, are made,
thus energizing the field of the polarized switch circuit con-
troller for the normal position of the switch, the motor cir-
cuit having been opened on the contacts of the motor cir-
cuit controller following the normal movement of the
switch. To reverse the switch, the lever is moved slightly
to the right, thus closing the lever latch contact illus^
trated at the top, and if there is no train on the electric
detector circuit and the detector track relay is consequently
picked up, the normal indication magnet will be energized
over the points of the detector track relay and contact NX on
the lever, thus freeing the normal locking segment; it wi)^

9n ALTERNATING CURRENT SIGNALING.

therefore be seen in this case the indication magnet N acta aa
a track circiiit lock tor if the track is occupied, magnet N can-
not be picked up, with the result that the nonnal indication
latch shown in Fig. 210 engages the normal locking segment
and prevoits further movement of the lever. Assuming then
that the track is unoccupied and that indication magnet N
can be picked up, the lever is then free to be moved to dose
the contacts RD which, acting as pole-changing contacts, as
previously explained, reverse the current in the field of the

Fi«. 221. Potyphue Indication Relay*. TIk« Together with the Ma-
chine Shown In Fig. 206 Onutiluu tha Eatin Town Equipaient Foi
a Type "F" Intcrlockinf at Pawdickat. R. I., on tha Naw HaTea
Railroad.

switch circuit controller, thus feeding current into the switch
motor for the unlocking, reversing, and relocking of the switch
points; when the switch is fully reversed and relocked, the
motor circuit controller opens the motor circuit and the motor
•tops. It is here to be observed that the wirea leading from
tht kotr eontatii to the twlUh circuit controller are trUirely iao-

TYPE "F" A. C. ELECTRIC INTERLOCKINC. $9$

Uded from the bus-mains. No common return whaieoer is used
and hence a false movement of the switch could only result
through a double cross of the bus-mains with thd switch oper-
ating wires; furthermore, this double cross would have to be
of the required polarity.

It will be observed from Fig. 210 said 219 that the move-
ment of the switch lever to the right after 'dosing the pole
changer contacts RD is stopped by the reverse indication
segment and latch. After the switch is completely reversed
cuid relocked, however, the indication circuit controller re-
verses the indication relay in the tower, thus energizing the
reverse indication magnet R over contact D and lifting the
reverse indication latch away from the upward projecting
shoulder on the reverse indication segment. The lever may
then be moved to full reverse, releasing the mechanical lock-
ing and permitting the corresponding signal to he cleared
over its lever. When the lever is moved from the reverse to
normal, the same cycle of operation is gone through, the re-
verse indication magnet R being first energized over the lever
latch and contact RX (providing of course the detector track
relay is picked up), thus releasing the lever to close pole-
changer contacts NB to throw the switch circuit controller
to the corresponding normal position; after the switch points
are thrown normal and relocked, the indication circuit con-
troller reverses the indication relay to energize the normal in-
dication magnet N over lever contact B as shoWn in Fig. 219.

It will be noted that the lower periphery of the normal and
reverse magnet indication segments shown in Figs. 2 1 0 and 219
are provided with a projecting shoulder; the |>urpose of this
shoulder is to cause the armature of the corresponding indi-
cation magnet to be forced open mechanically after each lever
stroke, thus introducing a positive safeguard against the arma-
ture being stuck closed. The actual latching of each magnet
is accomplished through the medium of the shoulder project-
ing from the top periphery of the indication segment. When
detector bars are used instead of detector circuits the lever
latch contact is omitted and the indication segments are so
cut that the lever may be immediately moved as far as the
indication position, being restrained there of course until the
switch is thrown and locked and the indication received ovei:

394 ALTERNATING CURRENT SIGNALING.

the points of the polarized indication relay and the lever con-
tact B or D, jbls the case may be.

The complete operating and indication circuits for a single
switch, are covered by Fig. 219; for a cross-over, the lever
contacts, etc., in the tower are identical, the two switch
controllers for their respective switch mechanisms at the
points being simply connected in multiple to the two control
wires ordinarily used for a single switch. The indication
circuit controllers are wired as shown in Fig. 220, and feed
current to the signal indication relay in the tower exactly
as in the case of the single switch.

12. ''SS" Control of Signals. It will be observed from
Fig. 219 that normally a current flow is maintained through
two contacts of the switch indication circuit controller in
one direction, and through two of its other contacts in the
opposite direction when the switch is reversed. This
current, through two isolated conductors which extend
to the polarized indication relay at the interlocking
machine, maintains a normally active state of that relay
to retain closed certain contacts and to retain open cer-
tain other contacts. Upon full reversal of the switch and
lock movement, a reversal of the flow of current is produced
by reason of the changed relations then occurring between
the contacting members of the indication circuit controller.
The polarized relay is thus caused to reverse its influence
upon its contacts said hence close those contacts that former-
ly were open and open those that were formerly closed. The
contacts of the relay thus repeat the two positions of the
switch and lock movement, and are therefore employed for
controlling not only the normal and reverse indication mag-
net of switch levers during switch operation by simple local
circuits, but may also be used as shown in Fig. 219 as a means
wholly within the interlocking tower to obtain a very simple
and effective control of the current supply to every signal of
the system by actual positions of each and every switch over
which it governs. This method is designated as the "SS"
control, and is obtained without recourse to any facing point
circuit controllers or additional conductors or devices ex-
emal to the tower which are necessary to other methods.

TYPE "F" A. C. ELECTRIC INTERLOCKING. 395

Obviously, this joint control of the indication mcignets and
that of the current supply to signals is not to be supported
upon the grounds of this simplicity alone. Inherent in the
method are elements of safety that insure immunity from
faulty operations arising from any causes whatever that make
it superior to any methods heretofore embraced in any power
interlocking for like purposes. Naturally, the relay should
be energized only when the switch is in one or the other of
its two extreme positions and securely locked there. To in-
sure that during the unlocked condition of the switch (cmd
during its operation) the relay will be energized with cer-
tainty, the indication circuit controller interrupts the cur-
rent supply to both indicating wires, and it also forms a shunt
or short-circuit between them of very low resistance as an
added safeguard.

By this method both indicating wires are maintained at the
same (zero) potential until the switch is positively locked in
one position or the other — the direction of current flow in
them being distinctive for each switch position and hence
positive in its selection of the indication magnet or signal
released by it. Tlie method is equally positive in its applica-
tion to a single switch, crossover or to any number of switches
operated by a single lever.

[ It will be observed from Fig. 212, that upon the assumption
that a signal lever has been operated to permit a train to
move over the switch, the switch lever shown is mechanically
locked in the position it assumes, and this secures the lever,
the switch circuit controller, the switch, the indicating cir-
cuits and the polarized indicating relay in the following re-
spective conditions; the lever normal; the switch circuit con-
troller normally energized; the switch held and mechanically
locked in the normal position; the two indicating wires main-
tained at different potentials of a given polarity; the polar-
ized indicating relay energized to close its normal contact;
a circuit emplojang one of the closed normal "SS" contacts
on the indication relay over which is carried the current supply
to those contacts actuated by signal levers that primarily oper-
ate the one or more signals that govern train movements over
the switch. ^

'- Obviously, under these conditions the switch lever can-

396 ALTPINATING CURRENT SIGNALING.

not be moved until the signal lever is placed normal and the
signal is in the stop position. The operation of the switch
therefore by its lever compels a prior act of the signal lever
which withdrawa or withholds train rights over the switch.
The operation of the switch by other means than its lever, as
by the malicious or accidental manipulation of its operating
mechanism, will be first accompanied by an interruption of
the electric energy in the indicating wires and then a shunting
of these wires against influence from foreign sources. This
produces a de-energization of the indicating relay, the etfect
of which is to cause it immediately to icut off the electrical
energy, through its contacts, by which each signal governing
movements over the switch is controlled, and thereby to place
at stop any such signal as may at the time be in the proceed
position, or, should all of them be in the stop position at the
time, prevent the operation to proceed of any such signaL In
other words, the improper operation of a switch in this man-
ner establishes the same condition of the indicating relay, as
is established by failure of it to operate properly by its lever,
and maintains that condition until the lever and switch are
made again to coincide fully in position. When in ordinary
operation the switch assumes a reversed position by virtue
of a partial reversal of its lever, the indicating relay becomes
again energized, but by current of a reversed polarity from that
existing when the switch and lever were normal. The effect
of this is to shift the polar contacts of the relay to establish
current through the reverse indication magnet and the closed
contacts of the quick switch, and thus to release the lever for
final movement to its full reversed position. This final move-
ment causes action of the quick switch again to open the cir-
cuit of the reverse indication magnet, and so to connect the
normal indication magnet with the normal contacts of the in-
dicating relay as to prepare that magnet for its next indi-
cating function.

13. Detector Track Circuit Locking. The control of
the indication magnets by the quick switch in this manner
involves the use of but one magnet at a time for indicating
purposes, and hence, leaves at all times one of the magnets
free for other duties if desired. It is this fact that prompted
tb« iJtem«^tive use of each indication magnet for detector cii^

TYPE "F, A. C. ELECTRIC IMTERLOCKING. 397

■ ■ - ■ I I ■_ I IIB.. . I I ■! ■■*

cuit switch lever locking by trains, and to render this elective
two contacts, NX and RX, Fig. 2 1 9, operated by the switch lever
ai;e employed, (sometimes designated as "X" and "Y" con-
tacts), for the purpose of throwing, alternatively, the indi-
cating magnets into circuit with the contacts of a track relay
that embraces the switch rails in its control. In this way,
trains entering upon the switch cause that one of the indi-
cating magnets that was last used for switch indicating pur-
poses to remain upon open circuit and therefore to prevent
initial movements of the lever, until the train has passed dear
of the switch. The locking circuit thus formed also passes
through a contact that is acted upon jointly by both the
catch-rod and the lever — ^a contact closed as the catch-rod is
elevated to energize the lock, if the track is unoccupied, and
which is opened again by the lever during its movements be-
tween its positions of engagement by the locks. This is done
by the latch to economize in current energy when the lever is
at rest in either the normal or the reversed position, and by
the lever absolutely to disconnect both magnets from ariy pos-
sible current influence save that peculiar to the indicating
system, as soon as the lever moves beyond the influence of
the automatic track circuit control of levers and into that
entirely separate field of control that embraces only the
switch indicating system.

14. Cross Protection. Because of the vitally impor-
tant functions performed by the indication system in the type '
"F** electric interlocking, i. e., first, the coincidence in posi-
tion of switch and lever before final lever movement can be
made, and second the continuous and active control of sig-
nals by switch position thereafter, every precaution that
could be consistently taken to insure reliability of action under
all probable conditions has been taken in its arrangement.
The separation of the indication circuit bf each switch from
electric contact with any part of any other circuit between
the switch and the interlocking machine, was the first step;
the use of individual circuits so arranged for each switch or
set of switches operated by a single lever was the second step;
the use of a current of one polarity for indicating one position
of the switch, and the use of a current of an opposite polarity
for indicating the other position of the switch, and mestns for

398 ALTERNATING CURRENT SIGNALING.

shunting or short-circuiting the two indicating mains at the
switch until the switch is properly locked in one or the other
of its two positions, constitute the third provision ; the fourth
provision embraces the use of the polarized indicating relay
at the interlocking machine so adapted as to control jointly
the current supply to both the indicating magnets of a switch
lever and to each and all signals governing traffic over the
switch or switches operated by the lever.

15. Switch and Lock Movement Layouts. Model 13
switch and lock movements may be applied to the operation
of switches of every character and rail section. Variations
in chstracter are exemplified by four commonly encountered
tjrpes: Derails, Simple Turn-Outs, Slip-Switches, and Mov-
able Frogs. The first two of these tjrpes involve no special
consideration in their operation by switch and lock move-
ments, the mechanisn shown in Fig. 2 1 3 serving the purpose.
The operation of movable point frogs, however, involves condi-
tions analogous to the operation of two single switches, the
theoretical points of which coincide in position, and the leads
of which extend in opposite directions. Switch and lock
movements adapted to movable frog operation, hence, must
operate and lock two sets of points. The points of each set,
furthermore, must move simultaneously, and in opposite di-
rections by independent connections, and they must also be
equipped with independent lock rods for insuring the direct
and individual locking of each set. With M. P. frogs it is
, therefore customary to operate one set of points from a single
switch movement (Fig. 215) and the other set from an external
switch and lock movement driven from the above motor move-
ment and consisting of the usual crank, operating rod and lock
rod, carried on a base plate bolted to the single switch move-
ment and housed in a small cast iron box; this arrangement is
really equivalent to a single long slide bar equipped with two
switch driving cranks and rods and a double set of lock rods
with their locking blocks.

When movable frogs are a part of a slip switch layout the
frogs are operated simultaneously with one end of the slip
switch, one set of frog points and the slip end each being pro-
vided with a switch and lock movement driven in** tandem
from the motor mechanism Fig. 2 1 5 located at and operating

TYPE "F* A. C. ELECTRIC INTERLOCKING. i^

^^""•"^^■^ ■ ' ■■■ ■ ' ■' ^^•^^^^^^^— ^i^»*^^— ^i^^— ^■^■^^^■^i— ■— ■^^■■-* I ■liana, ■—^^■^bbb ■- ^^^^^^^^^^^^^^B^^Ba^^^BaM^^^H^^^

the other end of frog points. The remaining slip end must of
course be driven independently from a motor mechanism. Fig.
215; it is, therefore, the custom in type **F" interlocking to
adapt a single motor to the operation of three switch and lock
movements in tandem in the case of slip switches with M.
P. frogs. Such an arrangement calls for electric contacts only
on the slip end mechanism for controlling the switch indicating
system, since the mechanism (being the one most remote from
the driving motor) can assume correct positions in response to
lever movements only in case the frog mechanisms have also
assumed such positions.

In the operation of slip ends individually (independendy
of the frogs, as is sometimes done) and in the operations of
single switches and derailing devices, a single switch and lock
movement complete is employed.

16. Detector Bars. When detector bars are required
they are operated by the first part of the mechanisms move-
ment, which although employed primarily for unlocking the
switch is also employed for the elevation of the bar above
rail level.' A train standing upon or moving over a switch
obviously prevents the elevation of the bar, and hence the
unlocking and movement of the switch under trains. During
that part of the slide bar stroke that affects switch operation,
the detector bar remains motionless in its elevated position,
and during the final movement to lock the shifted switch the
bar is depressed to its former position below rail level. The
bar is operated from the rod extending lengthwise out of the
case in Fig. 216.

Since detector bars constitute the chief loads to be met by
the switch motors of power interlockings their elimination,
upon the score of power economy and operating speed is de-
sirable. Since modem practice embraces, in power interlock-
ing, the automatic locking and releasing of switches through
the medium of detector circuits and sectional route locking
by train action in a manner that precludes the possibility of
switch levers being operated while trains are approaching or
passing over interlocked switches, the value of the detector
bar in this service is confined solely to cases where improper
or irregular lever movements are resorted to — as during block-
ades* wrecks, or like derangements. For these reasons de-

400 ALTERNATING CURRENT SIGNALING.

ttetor bars are not regarded as an essential feature of power
interlocking and the cost of their application and maintC'
nance usually exceeds the value of the protection they atford
in this field.

SIGNAL OPERATION.

17. Signal Mechanism. All types of A. C. signal
mechsoiisms as described in Chapter VIII are equally well
adapted for use in type *'F'* interlocking. In the case of the
Style B signal a motor current contact is attached to the slot
armature and normally holds the motor circuit open as ex-
plained in connection with Figs. 154 and 161, Chapter Vlll;
the slot coils are directly energized from the signal lever con-
tact and when so energized draw the armature up to the
slot magnet poles, closing the motor circuit to drive the sig-
nals to one of the proceed positions. The slot and armature
thus perform the dual duty of holding the signal clear and act
as a line relay, thus economizing in first cost, power and
space The Style "S" three-position signal may likewise be
provided with a slot contact for its caution position but not
for its full proceed position, since there is but one slot arma-
ture and it remains closed with the signal in the caution posi-
tion; a vane type line relay (Chapter IV) is therefore gener-
ally used to control the 90^ or proceed position. The Style
T-2 signal cannot, of course, be provided with a slot contact
and in this case a two-position or a three-position line relay
as may be required, are employed, these relays being con-
trolled directly from the signal lever in the tower. In most
cases a two-position line relay will be sufficient, €M the pro-
ceed or 90° indicator is generally secured from the signal in ad-
vance. The reader is referred to the wiring diagrams. Figs.
161, 163 and 167 for further information.

18. Signal Control. Since no special devices are re-
quired for signals in Type "F" interlocking, the control cir-
cuits are extremely simple and are plainly shown in all their
phases in Figs. 222 and 223. It will be seen that they are
very similar to those used in the electro-pneumatic inter-
locking system except that the negative or return wire for a
signal or group of signals on one side of a signal lever is carried
back to the machine and over a contact on the signal lever
roller. This prooides a separoU reUarn» without connedion io

TYPE "F- A. C. ELECTRIC INTERLOCKING. Ml

402 ALTERMATINC CURRENT StCr4ALlNa

TYPE "F" A. C. ELECTRIC INTERLOCKING. 403

* ■ ... ^

either of the bus-mains. Just as in the case of the control for
switches; this arrangement renders harmless a cross on mtiter of
the signal control wires.

Where two or more signals sire operated from a single lever
in Type "F** interlocking, each signal is made to interrupt a
common circuit including the electric lock on the lever, so
that all of the signals must be returned to the stop position
before the signal lever may be put normal and another route
set up. Tlie perspective diagrams. Figs. 222 and 223, illus-
trate this control of the lock circuit and also the manner of
selecting a number of signals, by switch position, for opera-
tion by a single lever. The control of signals in this manner
is made of two-fold value because of the double function of
signal levers obtained by their operation to their right (from
the central position) for routes of a given direction over a
given point, and to the left for routes of a reverse direction
which conflict with the first mentioned routes. The semi-
automatic control of a group of signals thus operated is pos-
sible for a single track circuit, frequently, and by mi^ans of a
single contact relay. These features are important in Uieir
influence to concentrate the control of many functions within
comparatively simple and hence trustworthjl^ instruments,
and are of especial value in route locking and in the control
generally of signals and lever locks by train action. (

19. Route Locking. In order to illustrate the basic
principles upon which sectional route locking is arranged and,
at the same time, to show its relation to other prospective fea-
tures of Type **F** interlocking, the diagram. Fig. 224, is pre-
sented. The track- layout is of the simplest form necessary
to the purpose, the two switches therein serving quite as well
as a greater number of switches in a more complicated track
plan to illustrate the automatic locking of all switches in a
given route and the individual release of each after the passage
of the train beyond the fouling limits embraced in the two
track leads of each. These two switches serve also to illus-
trate the principle of selecting signals by switch position,
when a number of signals are operable from a single lever. * It
will be observed from the plan that the rails of each switch
are included within separate track circuits, and that these cir-
cuits embrace both leads as far as their fouling points, and

404 ALTERNATING CURRENT SIGNALING.

F«. 224. SwtiDMl Route Lwkint Circi

TYPE "F" A. C. ELECTRIC INTERLOCKING. 4C>

extend in each direction to the signals governing the move-
ments over these two switches. A track circuit also extends
from the signal which primarily governs the first switch to
the preceding signal, usually called the "distant" signal. A
fourth section also extends from this distant signal to a point
preceding it 3,000 feet or more. These sections are desig-
nated on the plan by the letters D, C, B and A. The switches
are designated by the numerals I and 3, corresponding with
the numbers of the ^o levers assigned to their operation.
The signals are all (H!»erated by lever No. 2; the three east-
bound signals being operated by the lever thrown to the right
and the two arms of the westbound signal by the lever thrown
to the left — this being possible because each of these signals
conflict with each other signal under all circumstances.

Tlie operation of signal 2L-a for a westbound train requires
that switches 1 and 3 be set and locked as shown, before lever
2 may be moved to operate the signal. The operation of
lever 2 to the left through the mechcuiical locking of the ma-
chine locks levers 1 and 3 normal, and hence the switches 1
and 3 for the route governed by the signal so long as lever 2
remains moved from its normal position.

It will be evident, therefore, that even though signal 2L-a
be restored to the stop position by the partial return of the
signal lever toward normal, the switches of the route still remain
mechanically locked. It is evident, too, that whether lever 2
is retained out of its normal (central) position by choice or by
compulsion, the switches remain locked with equal security.

20. Approach Locking. The return of signal 2L-a to
normal, ordinarily, releases the lever for its restoration to nor-
mal; where route locking is in vogue, this release of the lever
by the signal's return is made dependent upon an added con-
dition. This condition is that a train has not, previous to
the signal's return, entered upon the track circuits A or B. If
the train has so entered, its approach is automatically an-
nounced to the operator by annunciator A'-B', and the elec-
tric lock of lever 2 is retained upon open circuit during the
train's presence upon either of the sections. Before the an-
nunciator A'-B' can be re-energized to release the lock 2,
the train must have left sections A and B completely. If its
leaving was by pe^mi^sipQ of 9ignal 2L, the train naturally

406 ALTERNATING CURRENT SIGNALING.

entered upon section C before it left section B. This act
causes, through relay C, the indicator D'-C to become de-
energized before the annunciator A'-B' becomes re-ener-
gized and releases the lock of lever 2 whereby that lever be-
comes free to be i^ut normal and the mechanical release of
switches 1 and 3 becomes possible. The release of lever 2
by indicator D'-C when this indicator is de-energized has
another important function. If a second train enters sec-
tion A-B before lever 2 is restored (this lever having been
throwh to clear signal 2L for a previous train), indicator
ly-C' will not pick up, being a "stick" indicator. The re-
lease circuit, through a back contact of indicator D -C, will
remain closed and allow the leverman to restore lever 2 al-
though the lock circuit of lever 2 is open through indicator
A'-B'. The signed lever may also be restored while &■ train
is in section A-B by the use of a time release, the operation of
which is described in a subsequent paragraph. Should lever
2 be restored to normal after a train has accepted signal 2L,
the release mechanically, of levers 1 and 3 that follows is with-
out danger, because the entrance of the train upon section C
(that necessarily preceded this event) caused, through relay
C, the interruption of the electric lock circuit of lever 1 , and
through stick relay C, the interruption of the electric lock
circuit of lever 3, thus effectually retaining these levers still
locked against operation, but by direct electric means peculiar
to each.

21. Switch Locking. While switch levers are thus
locked automatically in groups by train action upon the first
switch of the group, their release must occur not in like man-
ner by the exit of the train from the last switch of the group,
but each lever must be released individually as the train
passes over its switch and clear of the fouling limits of the
switch leads. The movement of the train westward off of
section C and into section D causes relay C and stick relay C'
to become re-energized and the electric lock of lever 1 re-
leased. Before this occurs, however, relay D has been de-
energized, by the entrance of the train upon section D in its
movement from section C, and hence the circuit of lock 3 is
continued open at relay D, notwithstanding its closure at
rday Q\ and lever 3 still remains locked until the train passes

TYPE "F" A. C. ELECTRIC INTERLOCKINa 407

entirely clear of section D and until relay D becomes thereby
re-energized.

It will be observed that stick relay D' is not operated with
relay D» for were this done, the lock circuit of lever 1 would
be opened thereby and the release of switch 1, which is de-
sirable, would not follow the train's exit from section C. Tlie
action of the train on section D, and the consequent de-ener-
gization of relay D, would not open the circuit of relay D'
because of a "by-pass" formed by lever 2 when that lever is
not in a position for governing eastbound traffic. This by-
pass bridges the open contact of relay D and prevents the
action of relay D for westbound traffic; when lever 2 is thrown
to the right, however, for signaling eastbound traffic, the
train's action upon section D operates not only relay D, but
also the relay D', thereby opening the lock circuits of both
levers 1 and 3. Upon passing on to section C, relay C only
is de-energized and not relay C', as when the westbound train
entered section C from section B. Relay Qf is thus retained
in an energized state by virtue of a by-pass formed by lever 2
when that lever is in any position other than that employed
for eastbound traffic, cmd hence when the train moves from
section D intd section C, the re-energization of relay D closes
the lock circuit of lever 3 and releases switch 3 for possible
operation. This would not occur did not the relay C' re-
main energized, through the by-pass referred to. The lock
circuit of lever 1 is necessarily opened by relay C before the
eicit of ^he train from section D into section C fully occurs,
so that after the occurrence, when both relay D and relay ly
are energized, the circuit of lock 1 remains open at relay C
and until the train passes clear of section C, whereupon switch
1 may be moved if desired.

It will also be observed that when switch I is reversed, a
byrpass is established on stick relay D' which causes this re-
lay to remain energized regardless of the condition of track
rele^y D. The purpose of this by-F>ass is as follows: With
switch 1 reversed and a westbound train having not yet
cleared section D, if signal 2R-c were cleared for a second
train to move from siding CS to the main line, stick relay D
would open if it were not for thi^ by-pass said switch 1 would
be locked and remain locked as long as the first train stood on
section D, thus preventing all movements of traffic over

m ALTERNATING CURRENT SiCNALINC.

'>_ -■

switch 1 in its normal position. A similar by-pass acts on
stick relay C' and prevents switch 3 from being locked while
a train is passing into siding CS after having accrepted signal
2L-b« This latter feature is not very important with this
particular layout, but with a more complicated arrangement
of tracks and switches it is essential to prevent the tying up
of several parallel train movements under the conditions
cited.

22. Approach Detector and Section Locking. That
feature of automatic lever locking by trains, which is peculiar
to the action of trains prior to their entrance upon the switches
of the interlc)cking, is generally referred to as approach lock-
ing, and embraces also the automatic announcement of trains.
That feature which involves the action of lever locks by train
movement over the switches of the interlocking, is generally
termed detector locking and sectional route locking. The
latter feature embraces, besides the automatic locking and re-
leasing of switch levers, the semi-automatic control of sig-
nals by trains through the medium of track circuits conunon
to both.

23. Calling-on Arm. In the diagram. Fig. 224, the cir-
cuits peculiar to the operation and control of the two west-
bound signal arms only are shown in the interest of simplicity.
The top arm only is under automatic control by trains
(through the indicator D'-C), since the lower arm is here
assigned to movements into either one of the two sidings
whether these be occupied already or not, and also to the
main track D, only in case that track is already occupied, and
the top arm is hence restrained against operation by indicator
D -C', for such train movements. The use of the lower arm
in this capacity is as shown not (XMsible by lever action alone
but demands in addition the operation of a push button
which is mounted behind the signal lever so that its operation
is convenient only when the lever is moved from normal — a
movement that must necessarily precede the effective use of
the button for clearing the "calling-on" arm. This button,
when depressed, closes a pair of contacts in the signal circuits
that are effective to clear the calling-on arm providing the
high speed signal above it is in the stop position, and provid-
ing also that the signal lever 2 is moved to the left.

TYPE "F" A, C. ELECTRIC INTERUXKING. 409

Ml .11 II''- --- .-.. . ■

24. Time Releases. The current supply to both arms
is also drawn through contacts of a device known as a
"time release," Fig. 236, Chapter XII and already
referred to in in a general way. This is done in order
to insure that the first act of its operation will be to open
the signal circuit and thus prevent any possible operation of
the signals until the device has been again returned to its
original position. The operation of the time release to un-
lock electrically during emergencies a lever properly held
locked by train action, requires first, a distinct action by the
leverman, and second* that a sufficient period of time must
elapse, following this action, to insure that the train, which
is locking this lever, hits either stopped or is traveling at a re-
duced speed, before the lever is restored to its normal position.
It is also to compel the restoration of the time release to its
normal pos^on after each operation (before signals can be
again, operated for traffic movement under them) that sig-
nal circuits are thus controlled by contacts on the time re-
lease. The current supply to both signals is further drawn
through contacts of other devices than the indicator D'-C
and the time release. \ In order to insure that a misplaced
switch, wrongfully set from any cause out of coincidence with
the new position of its operating lever, and to insure also that
a lever which from any cause assumes a position at variance
with that of the switch it operated, may effectually prevent
the display at such times of any signed giving proceed rights
over the switch, this current supply is also drawn through the
contacts of the switch indicating relay and through corres-
ponding contacts operated by the switch levers.

25. Laying Out Plant. In adapting the Type "F" inter-
locking system to the requirements of any particular track
and signal lay out, the first step is to group the switches for
operation by the least number of levers possible, numbering
the switches to correspond with the levers assigned to their
operation. The second step is to group in like manner the
signals for operation by the least possible number of levers,
numbering the signals to correspond with the levers assigned
to their operation. The switches and signals being thus des-
ignated clearly by the number of their operating levers and
the size of the machine being thereby established^ the mechan-

410 ALTERNATING CURRENT SIGNALINO.

ical locking of one lever by another or t>y others is next worked
out, as in mechanical interlocking practice. This constitute;
the third step in the development of an interlocking. The
mechanical locking of Type "F" machines is greatly simplified,
as compared with that which would be required of a purely
mechanical machine adapted to the same track and signal
layout, by reason of the much greater capacity per lever of
the former and the consequent reduced number of levers it
requires.

26. Track Circuits and Electric Locking. The fourth
step consists in subdividing the track layout into track sections
in such a manner, that, as far as is practicable, the rails of each
pair of diverging, converging or intersecting tracks shall com-
prise a separate section throughout that portion of each
wherein each fouls the other. Track sections are also formed
of rails of tracks lying between the sections referred to, and
these track sections are primarily for the automatic locking
and releasing of switch levers by trains (in lieu of de-
tector bars), but are also utilized for the semi-automatic con-
trol of signals by trains, where this practice is employed.
The fifth step consists of laying out the detailed circuits for
the control of signals, approach locking of signals, detector
and sectional route locking of switches, etc., according to the
requirements as described in these paragraphs.

27. Locking Between Towers. The first requisite of a
safe method of preventing the simultaneous entrance of trains
from opixMite directions onto a piece of common track is the
interlocking of the two signal levers by which movements to
such a track are governed. When both levers are comprised
in a single machine (both signals embraced in the same inter-
locking) this interlocking is done mechanicedly and in a very
simple way well understood. When, however, the levers
constitute elements of two separate machines (the signals em-
braced in two different interlockings), the locking is not prac-
ticable by purely mechanical means and is accomplished elec-
trically. Usuedly, more than one signal governs train move-
ments for each interlocking over a "gauntlet" track. To
obtain the simplest circuits and the least number of instru-
ments, contacts, etc., for the protection sought in such cases,
an independent lever in each interlocking is employed as a

TYPE "F** A. C. ELECTRIC INTERLOCKING.

41!

«« . »»
msister

lever and it is to those levers that the electric lock-
ing is applied — these levers (through the mechanical locking
of the machine) being locked by each signal lever of the ma-
chine giving train rights over the gauntlet track. In the as-
sumed case, shown in the diagram. Fig. 225, Lever IL of
Tower "B" and lever IR of Tower "A" are the master levers
while 2L and 4L are the actual signal levers of Tower **B**
and 2R and 4R are those of Tower "A."

Fig. 225. Check I.ocking Between Towers.

Between the signals of the two towers a track circuit is
formed that controls directly an indicator in each tower. The
indicator informs the operator at each station of the entrance
and exit of trains from the track sections lying between them.
They also serve as means for the direct semi-automatic con-
trol of the signals of each tower by trains. Primarily, how-
ever, these indicators are employed foi the control of the elec-
tric locks of levers I R and 1 L by train action upon the gaunt-
let track. The direction of traffic over the track is establish-
ed by joint action of both towermen in placing their respec-
tive "mastet" levers in proper predetermined positions.
While both towermen must thus co-operate to establish con-
ditions essential to any given direction of traffic, each oper-
ator has full power to control the signal indications of his

412 ALTERNATING CURRENT SiGNALINa

* — — — — ■»

own apparatus— granting or prohibiting train movement to
the gauntlet track at will after consent of the opposing tower
has been obtained. In this control, however, he is restrained
from either intentionally or accidentally granting to his
neighbor the right to use the gauntlet track until it is wholly
unoccupied by trains, and until all signals governing move-
ments to it are at stop, and their operating levers are n the
normal position. With these conditions prevailing, that one
only of the master levers which granted permission for traffic
movements from the tower remains free to be operated at will.
Upon the reversal of this lever a similar lever in the opposing
tower is electrically unlocked and is then free to be shifted to
release mechanically those signals at that tower by which
a like unrestricted use of the gauntlet track is reserved to
train movements to and from it under the signals of that
lever exclusively.

Thus the gauntlet being unoccupied, and each towerman
being made aware of this by his indicator, A may desire to
move a train under signal 2R to B. This he can do under
the conditions prevailing, because signal lever 2R is free to
be moved when master lever !R is thrown to the right as
shown. This action of lever 2R, however, operates the sig-
nal only upon condition that the current supply to the signal
is not interrupted by either or both of the tower indicators.
A train acting upon the authority of signal 2R operates that
signal automatically to stop through the medium of the track
circuit and the tower indicators controlled therefrom, and
simultaneously retains the locks of levers 1R and 1L upon
open circuit until it passes completely from the track circuit.

While levers I R and 1 L may at any time be placed in thetr
central position, that one at A (l^ver 1 R) may be moved only
to the extreme left at all times, while that one at B (lever !L)
may be moved only to the extreme right at all times. The
application of the electric locks to these levers by train action
restrains but one of the master levers against full reversal.
For the direction of traffic shown in the diagram lever 1L,
Tower "B,** is so restrained, while for traffic in the opposite
direction lever IR, Tower "A,** is likewise restrained.

When the train has passed clear of the gauntlet track sec-
tion both indicators give evidence of the fact and the master
levers may then be operated to change the direction of tralBc

TYPE "F" A. C. ELECTRIC INTERLOCKING. 413

<■ ■ .

Reversal of 1 R locks mechanically signals 2R and 4R against
operation while reversal of 1L releases signals 2L and 4L for
operation. A westbound train now acting upon authority of
signal 2L or 4L de-energizes both indicators and retains both
electric locks upon open circuit as before. Now, however, it is
lever !R that is restricted against full operation in reverse
by the train until the latter has passed clear of the gauntlet
section — thus automatically holding traffic over the gauntlet
to conform with its own direction.

28. Complete Circuits for an Example Plant. Fig.
226 shows a complete small interlocking plant together with
track circuits for the control of the various features of the
system. Figs. 227 and 228 show the complete controlling
and electric locking circuits for this plant. These features
have already been described in detail and are typical of stand-
ard practice.

4H AI.TERNATINC CURRENT SIGNALING.

rsL^-rlf

-.■-=a»

TYPE "F" A. C ELECTRIC INTERLOCKING.

• F«. 2Z7. Signal CeoUvl Circ

416 ALTERNATING CURRENT SICNALINa

CHAPTER XII.

AUXILIARY APPARATUS USED
IN A. C. SIGNALING.

CHAPTER XI I.

AUXILIARY APPARATUS USED

IN A. C SIGNAL SYSTEMS.

A. C. SWITCH INDICATOR.

"Z" Armature Type.

Fn. 229.
POWER BEQUIRED.

^SSi 1 "»""'»

"v';&-

A.„.

Watte.

!!8 1 SS

0.24

3.0
2.0

ACCESSORIES. 419

A. C. SWITCH INDICATOR.
"Z" ARMATURE TYPE.

The operating movement of the switch indicator, illustrated
on the preceding page, consists of a laminated bi-polar field,
in the bore of which turns a laminated *'Z" armature 14, in
the right hand (back) view; when the field coils are ener-
gized, the magnetic lines of force tend to shorten their path,
and, in so doing, cause the "Z** to turn in a clockwise
direction, when viewed from the back of the case, until
its middle leg is in a horizontal position, when, of course,
the magnetic path for the lines of force is the shortest from
one pole of the field magnet to the other, and the turning
movement of the "Z** ceases. A large air gap is provided for
the Z to swing in, and the entire mechanism (blade and all) is
mounted on a quickly removable plate, painted white on the
front to form a background for the indicator Uade.

The case may be provided with either a plain glass front or
a wire shield may be provided to protect the glass against
breakage, as illustrated in the photograph. By the employ-
ment of the proper cranks, the "Z" armature can be made to
swing the indicator blade in the upper or lower quadrant
through any required angle. Space is provided in the case
above the operating movement for either two Spark Gap
lightning arresters, (Fig. 233) as shown, or for two front and
two back relay contacts, easily operable from the armature
through the addition of a connecting crank.

ALTERNATING CURRENT SICNALINC

A. C. TOWER INDICATOR.
"Z" ARMATURE TYPE.

F!«. 230.

The operating movement of the above indicator, it will be
noted, is of the"Z" type previously described in connection
with the "Z" type switch indicator; in the present case the
bar carrying the contact Cngera is operated from the "Z" by
a vertical Unk attached at its upper end to a crank on the
armature shaft, the semaphore blade, or disc, being operated
by a small up-and-down rod attached at its bottom end to a
finger carried by the contact bar. The instrument illustrated
above is built for four front and four back high voltage
CMitacts: a wider instrument of similar design cariying eight
front end nght back contacts, or any combination there^.
can also be furnished.

POWER REQUTBED.

Normal
Voltage

Contacts

p,«,u.„ 1mi;|»™ a„p.. m.-.

110

1:8

A. C. TOWER INDICATOR
VANE TYPE.

This indicator is provided with a movement niacdy similar
to that used in the well known vane relay, and is, thereEore,
inunune to direct current. The instrument can be supplied
with any number of contacts up to four front and four back,
and with either a semaphore or disc indication.

POWER REQUIBED.

Normal
Voltage

■Watts.

110

J [ iS ] S 1 8:;S

!2 ALTERNATING CURRENT SIGNALING.

UNIVERSAL SWITCH CIRCUIT CONTROLLER.

F«. 232.

IliiB controller may be equipped with two-position con-
tacts to suit it for controlling line circuits or shunting A. C.
Bteam road track circuits, or three-posidon contEicts may be
provided to adapt the box far selective purposes at turnouts.
With either attangement. five independent sets ol contacts
can be furnished.

The side o( the box is cut out in the above photograph to
illustrate how a very accurate and permanMit adjustment
may easily be made; the segments pinned to the shaft carry
pinions, each of which mesh in a rack cut on the inner face <d
its segment, the pinions themselves actuating cams which
operate the contacts. An accurate micrometer adjustment is
thus secured. The trunldng leeda into the cap, or cover,
shown bolted to the left side of the box. this cover being trans-
ferable from one nde of the box to the other, as the switch
layout may require. "^ . '

Hs- 233.. Model 12 Ei«l

ALTERNATING CURRENT SIGNALING.

MODEL l^.^
A. C. ELECTRIC LOCK.

Fig. 233b.

The nbove lock is applicable to mechanical interlocking
machines o( the horizontal or vertical locking types. Its oper-
ating movement consists of an armature actuated by a horse-
shoe electro-magnet, whoae poles are equipped with shading
bands exacdy similar to those used on tractive type slot mag-
nets described in connection with Fig. 153. Chapter VIll.
The lock is designed for six independent circuits.

The lock is energized only for an instant while the indica-
tion is being taken; the amount of power used is hence of
little consequence and it has not been consideaed advisable to
complicate the design to secure a more economical but less
simple mechanism.

POWER REQUIRED.

,™.™c.

Normal
Volta«B

Voltage

A„...

Watts.

!1S

IS:S

ACCESSORIES.

Fw, 234. Model 14 Kcritans Iiuulated Rail Job

K(. 2J4t Modd 14 Keyalou liuuloMd Rul Joint.

P«rt»

Number of part*
for one Joint

4 Hole

6 Hole

I
2

1
8
2
2
4
8

G Fibre end post

J Steel heat treated bolt with nut. . - .
K <:>».l w..l».-

426 ALTERNATING CURRENT SIGNALING.

KEYSTONE INSULATED RAIL JOINT.

!• Construction. The Keystone joint has come into
very general use where great mechanical and electrical strength ,
combined with durability, are required. Heavy rolled steel
splice bars and fillers, illustrated in the cross section in Fig.
234, provide as much resistance to both vertical and horizontal
stresses as is found in the best designs of non-insulated joints;
thus, the danger of failure under moving trains due to the
breakage of the rail through bolt holes is minimized to the
utmost and a smooth riding track is assured. The bolts fur--
nished with the joint are subjected to a special heat treat'
ment whereby their strength is increased 40 per cent, above
that of ordinary bolts. Due to this great increase in strength,
the bolts will not "draw** and, besides eliminating the neces-
sity of frequently tightening the nuts, the joint is alwajrs
held tight, this naturally preventing the insulations from be-
ing chafed and worn.

All insulations, except a strip under the rail head, are of the
best quality of fibre obtainable and, due to the conformation
of the fillers and angle bars, the load is evenly distributed
over the entire contact area of the fibre; the unit surface load
on the fibre is, therefore, comparatively small, so that the in-
sulations are long-lived. Under the raiL head, on the gauge
side of the joint, where the load is the greatest, is placed a
strip of insulation known as Bakalized Canvas; this material
consists of compressed built-up layers of close woven canvas
impregnated under heat with Bakalite, a heat and absolutely
moisture proof synthetic compound possessing great insulat-
ing value. Bakalized canvas will, therefore, not crack, as it
is built up from a more or less flexible fabric base, and, in
addition, it is moisture and heat proof. Keystone joints
equipped as above have, in many cases, stood up two years
under heavy traffic without requiring any insulation renewals
or other attention whatever.

2. Instructions for Applying Keystone Joints*

First: — ^The rail end should be square and free from fins or
projections. Rails with sawed ends only should be used with
insulated joints. Sharp projections should be carefully chipped
otf at all places where they come in contact with fibre parts.

ACCESSORIES. 427

- — - - - ■ ■ ""

Any ordinary tie plates which may be on the ties supporting the
rail ends must be removed. If a tie plate is required, the in-
sulating type of plate on U. S. & S. Catalogue Plate M-1 is
recommended.

Second: — Assemble outside half of joint with fillers, bolts,
bushings, and top fibre plate, put bottom fibre plate in pos-
ition on rail, and apply parts, care being taken to see that the
turned up portion of the bottom fibre plate is between filler
and splice bar.

Third: — Insert end posts between rail ends. Rail end
should press firmly against end post.

Fourth: — Put bottom fibre plate in position on gauge side of
rail, slide gauge side splice bar over projecting bolts, insert
bushings, put on steel washers and nuts, and pull joint up part
way. The bakalized fabric plate can then be either dropped in-
to place from top or slid in at end of joint to suit convenience*
and joint tightened up.

Final Adjustments.

1 St. ^ After assembling, tighten nuts uniformly beginning at
middle of joint.

2d. Sledge splice bars on both sides of rail, and tighten
nuts again.

3rd. Tap bolt heads lightly with spike maul and tighten
nuts again.

4th. Tamp the joint ties up to rails.

5th. Tighten nuts again in three or four days and again in
ten days.

The fibre washers and tubes should not be separated, but
should be applied as a unit. If separated, the ends of the
tubes will probably be battered to such an extent in driving
them over the bolts that the washers will not pass over them,
with the result that when the nuts are screwed up, the pressure
will come on the ends of the tubes instead of against the splice
bars. A short piece of pipe, used as a set to drive the bushings
into position will prevent damage to either tubes or washers.

Particular attention is called to the importance of bring-
ing the ties up to support the rail end at the insulated joint.
No rail joint, whether insulated or not, can be expected to
stand the strain of keeping the rail ends in surface indefinitely
if the ties underneath it give no support.

ALTERNATING CURRENT SIGNALINC.

SPARK-GAP LIGHTNING ARRESTERS.

FLg. 235.

Tlie working unit of this arreater, illiutrated in the bottom
view above, consists of a-short sheet mica plate, provided at
^ther end with terminal lugB and projecting ears, which sup-
port between them glasa tub«s. into «Bch of which are slipped
two ordinary pins spaced with a ■^" air gap between
them; the pins and tubes are carried in a clip which is
easily removed when it is necessary to renew the pins
after their points have been burned off by lightninK dis-
charges. The arrester, shown on its porcelain support
with terminals, in the top view, is thus provided with six
multiple air gaps, and is very sensitive, discharging to ground
at a voltage well below the potential which the insulation in
ordinary signal apparatus is built to withstand. Many thous-
ands of these arresters are in service, and it has been proved
that, while lightning discharges may bum the pin points com-
pletely off, the pins will never fuse together. The points may be
easily inspected for separation through the glass, and can be
quickly renewed at a few cents cost. On ordinary line cir-
cuits. one terminal of the arrester is connected to ground
and the other to the line to be protected. In the case
of track and line relays, it is. however, a customary practice
to connect the lightning arrester directly across the relay, the
idea bnng that, due to the enormous impedance of the latter
on a high frequency lightning discharge, the lightning is choked
out of the relay and is shunted across the spark-gap before the
potential can rise to a serious value.

CLOCK WORK TIME RELEASE.

Fir23&

The function of this instrument is dearly described on pass
409. The mnximum time interval which can be Mcured i*
four minutes, and the design is such that the interval cnn be
vnried to any time between that amount and zero by the ad-
justment of stops contained within the instrument-
As will be noted from the photographs, a graduated dial
and clock hand are provided So aa to indicate St all times the
length of time which has eUpaed since releasing the knob>
Provisicxi is made in the instrument for the cmtrol of four
independent circuits, two at the zero or extreme right hand
position of the pointer, and two at whatever time it may be
set for. The turning of the knob to the right winda up the
clock mechanism a sufficient amount to always bring the
pointer bock to the time deaired after the knob has been re-
leased.

The instrument is made in two forms; one in which the
pointer stands normally at whatever time interval it ia de-
sired to secure, and the other in which the knob and pointer
•re latched at zero. In the former type the operator merely
tuma the kitob to zero and releases it, permitting the clock
work to restore it to the time desired. In the second type, th*
operator, after turning the knob to zero, give* a small mov*-
ment to the left to rdeue the Utcb. whoi it will autoowticBlly

430 ALTERNATING CURRENT SIGNALING

return to the time desired. In neither type» however, is the
operator able, by turning the knob to the left, to vary the
time required to etfect the release.

It will be noticed from the foregoing, that the second type
of release equipped with a retaining pawl or latch can be used
for the same purposes as the type without such an attachment,
since the operator can, after turning his knob as far as it will
go to the right, give it the slight left hand turn necessary to
release the retaining pawl in practically one operation.

In addition to hand operation, this release can be operated
by the lever of any type of interlocking machine by substi-
tuting an attachment in place of the knob and omitting the
retaining latch entirely*

ACCESSORIES. 431

ELECTRICAL MEASURING INSTRUMENTS
USEFUL IN A. C. SIGNAL WORK.

1. Measurements to be Made. In order to obtain ac-
curate information as to whether the apparatus in an alter-
nating current signal system is receiving the proper ener-
gization, the following measurements often have to be made:

L Voltage Across —

1. Motor, slot, line relay, and primary of track trans-

former.

2. Local element of track relay.

3. Track element of track relay.

4. Rails opposite track transformer.

5. Track transformer secondary.

IL Current Fed
i 1 . Motor and slot.

;

2. Track from track transformer secondary.

2. Instruments Required. Considerable care should be
exercised in the selection of meters, particularly as regards
scale and resistance, as otherwise the deflections may not be
easily read, and, furthermore, may not indicate accurately
the quantities under measurement, if the meter is such as to
alter the circuit conditions when it is connected in. These
points have been given due attention in the preparation of the
following list, which covers meters having characteristics suit-
ing them to the measurements outlined in the preceding para-
graph. For lack of space, only three standard makes of instru-
ments are referred to, although there are, of course, many
others which will meet the requirements.

L Voltmeters.

Where very accurate readings are required, as in the case of
field investigations carried out directly from thie signal engi-
neer's or supervisor's office, a mejier of the Weston Model 341
type (Weston Ellectrical Instrument Co., Waverly Park, N.
J.), or the General EJectric P-3 type (General EJectric Co.,
Schenectady, N. Y.), will be found useful. These instru-
ments should be provided with a 7.5^-30^ double scale and a
five multiplier for the 30 volt scale, so that voltages of 0-7. 5^,
0-30'' and 0-1 SO'' can be measured. The 0-150 volt scale
serves for the measurement of the voltage across the motors

4)2 ALTERNATING CURRENT SIGNALING.

•lots. lin« rdays, snd track tranaformer primariea, the normal
potential across their terniinals being usually 1 10 volts. The
0-30* scale can be used to measure the voltage across the sec-
ondary of the track transfonnei' (when over 7.5 volts), the
voltage nt die rails opposite the tr«ck tnosformer, and,
finally, the voltage across the local cmI of the track relay in
those case* where this element is wound for low voltage oper-
ation; otherwise the 1 50 volt scale can be used (or this latter
measurement. The 7.5' scale can be used for measuring
the voltage nt the transformer end of the track circuit (when
under 7.5 volts)
and also the vcdt-
age across the track
terminals of the
track relay in all
cases except where
polyphase relay s are
used on steam or
electric roads; the
track element volt-
age of these rdays
is so small <0.6 vcAt
or less) that they
cannot be read ac-
curatdy cm the 7.5
•cale, the lowest

•caU marking thov- p^. 237. w««.r. Modd J30 Prntabl. Hi,b
M> being generally RwBtance A. C. Voltmster.

one vcJt. The pow-
er taken by the track dement is so small in comparison with
that taken by the meter that were the latter provided with a
low readingscale. the corresponding winding would have such
a low resistance that the insertion of the meter across the relay
would cause a relatively large drop in the rails of the track
circuit: thus the voltage indicated by the meter would be
considerably below that existing across the relay before
the meter was connected in circuit. For such work, a special
high resistance voltmeter is required, and oae of these, the
Weston Model 330, is shown in Fig. 237; it is provided with
four scales, reading 0-1, 0-5 0-10 volts, and 150 volts, and
baaa resistance of 20 «hnu per volt, whereaa the Weston

Model 34 1 and General Electric P-3 meters {Mevioudy men-
tioned liave reuBtanceB of about 1 2 ohms per volt.

For the use of mamtBiners. either the General Electric Type
P-8 (Fig. 236) voltmeter, or the Weston Model 155, will be
found satisfactory. Theae instruments are less expensive and
less accurate than the Model 341 previously described, but
should be provided with the samescales and multiplieri they
however cannot be
used for measuring
the voltage across
the track terminals
of polyphase track
relays, for when
provided with the
low reading scale,
their internal resist-
ance would be ao
low as to alter the
circuit conditions
imvnediEtel" the in-

nected in. For this
'I* service, only an in-
strument of the
Weston Model 330 type, or one of equal resistance, will give
satisfactory readings.

II. Ammeters.

The full set of voltage readings secured as described above
will generally give sufficient information as to whether proper
energy is being delivered to the signal apparatus, and. in
most CBBCB. current readings may be dispensed with. However,
it is occasionally necessary to measure the amount of current
flowing in a signal motor or slot, particularly if it is suspected
that some of their cinls are short-circuited, in which event an
ammeter would quickly indicate that they were talcing ex-
cesnve current. Occasionally, it is desired to measure the
current fed into the track from the track transformer seccmd-
ary. For steam road work, an ammeter fo the Weston Model
155 type, or the General Electric Type P, will be found sat-
isfectory. These instruments should be provided with a O-f

434 ALTERNATING CURRENT SIGNALING.

ampere scale, so that they will give a fair reading on the
motor current (2-3.5 amps.), the slot current (about 0.5 amp.)»
and the current fed into the track by the transformer* the
value of which may run from a very small current up to 10
amperes, depending on the length of track circuit, ballast
leakage, and tyi>e of relay. On electric roads with impedance
bonds, the above meters may require auxiliary current trans-
formers when the current fed into the track is to be measured,
as this may run as high as 50 amperes in the case of long track
circuits equipped with impedance bonds of heavy current
carrying capacity and relatively low impedance.

III. Combination Meters*

A convenient combination meter for field service is manu-
factured by the Roller Smith Co.. of Bethlehem, Pa., this
meter being provided with the following scales:
Amperes 0-3, 0-12. 0-60.
Volts 0-6. 0-30. 0-120, 0-240

This instrument is free to a very considerable degree from
the influence of direct current, and it thus becomes available
for use in making alternating current and voltcige measure-
ments on D. C. electric road track circuits, where direct cur-
rent and alternating current are flowing simultaneously through
the circuits to be measured.

All the instruments described above will indicate on both
direct and alternating currents; if these instruments were used
in making measurements on single rail electric road track cir-
cuits, in which there is a considerable D C. propulsion drop,
the reading will be higher than it ought to be, as it will be the
result of the steady direct current superimposed on the alter-
nating current wave.

As far as the writer knows the Roller Smith instrument here
referred to. is the only one which can be used for work of this
character; it will give approximately accurate results, al'
though it is not absolutely free from the influence of direct
current. Of course, the Weston and G. E. instruments will
give absolutely accurate results, provided the direct current
can be cut otf while the A. C. readings are being made.

IV. Phase Meters.

It will be remembered from the discussion given in Chapter
IV that the highest e£&ciency of track circuits equipped with

two-element relays results only when the currents in the track
and local coils of the track relay are in proper phase relation-
ship. In order to secure highest track circuit efficiency it
therefore becomes necessary to occasionally make phase read-
ings, and the instrument shown in Fig. 239 is designed for this
purpose. The instrument itself is provided with two windings
one of which ia to be connected to the track element of the re-
lay and the other to the local of the relay, the dial of the meter
being graduated to show the phase relationship of the track
and local voltages; knowing the power factor of each element
of the relay it is then a simple matter to determine the phase
relationship of the currents as it is the currents and not the
voltages which determine the efficiency of the relay. The in-
strument could be designed to indicate currents instead of
voltages, but it would not be of sufficiently high internal resist'
ance and might consequently eflect the track circuit condi-
tions immediately it were connected in. The phase meter
here shown can be utilized in connection with relays either of
the gavlanometer or of the polyphase 4*96. It is mantifac-
tured by the U. S. & S. Co.

CHAPTER XIII.

TRACK CIRCUIT CALCULATIONS-

CHAPTER XIIL

TRACK CIRCUIT CALCULATIONS.

1. GeneraL The proper calculation of the track circuit is
of prime importance in the design of an alternating currentsignal
system as it enables the engineer to select that t3rpe of track
circuit apparatus which will operate most economically under
the particular set of conditions in question. Furthermore,
aside from the matter of economy, maximum safety of the
track circuit can only be guaranteed by proper track circuit
adjustments as dictated by the calculations. The process of
calculation is not at all difficult and the simple formulae and
diagrams here presented should enable the reader to make a
full analysis of any t3rpe of circuit operating under any condi«-
tions he may encounter.

2. Resistance, Reactance and Impedance of Rails.
The track circuit is in reality a small single^^hase transmission
system whose two line wires are represented by the rails, and
^t^ose load is represented by the relay at the end of the track
circuit. Like the line wires of the transmission, the rails
possess impedance (Z) composed of resistance (R) and re-
actance (X); the effective resistance of a steel rail is, however,
from three to five times the actual resistance to direct cur-
rent, due to the fact that the flow of alternating current in the
magnetic material of which the rail is composed, sets up a
magnetic field producing a counter e. m. f. in the body of the
rail itself, forcing the current to the outer surface or skin of
the rail, rendering thereby but a fraction of the cross-section-
al area Available for conducting current. This is known as
the "skin effect," and is present in a greater or less degree in
all conductors carrying alternating currents.

A further increase in the apparent resistance of the rails is
introduced by their self-inductance, this depending on the
spacing of the rails and their size, just as in the case of the
two wires of a transmission. Since the rails are magnetic,
however, their respective fields will be considerably more
localized around each conductor than would be the case if
non-magnetic conductors were in question, and hence, as ex-
plained in Chapter IX, the reactance of the rail circuit Mrill

440

ALTERNATING CURRENT SIGNALING.

TABLE L

IMPEDANCE OF BONDED RAILS TO SIGNAL CURRENTS
IN OHMS PER 1000 FEET OF TRACK.

ar'S-ft. nils

30-ft.nUi

■

J^-ftfAlll

• 1

Boodisc*

as-^

60^

as^

<&9W

as-^

60^

M
9.XO

P.P.

0.40

o.as

PJ.

P.F.

0.25

PJ.

P.F.

0.40

To capacity..

0.40

O.XO

0.40

O.IO

0.40

0.25

2 No. 6 copper..*...

0.X3

0.73

0.28

0.^

0.13

0.70

0.28

0.56

0.13

0.6q

0.27

O.S4

I No.8iroa I

I No. 6 copper. . . >

100

0.17

0.83

0.30

0.65

0.16

0.82

0.30

0.63

0.15

0.79

0.29

0.6a

2 Nb. 6c.c.— 40%.

0.19

0.87

0.3a

0.69

0.X9

0.86

0.32

0.69

0.17

0.84

0.31

0.68

7 No.6c.c.— '30%.

0.3S

0.91

0.36

0.75

0.22

0.91

0.35

0.74

o.ao

0.88

0.34

0.73

3 No. Siroo

0,40

0.97

0.50

0.88

0.36

0.96

0.47

0.87

0.34

0.96

0.44

0.85

To capacity

O.IO

0.43

0.26

0.43

O.IO

0.43

0.26

0.43

O.IO

0.43

0.26

0.43

2 No* 6 copper

0.14

0.73

0.29

0.58

0.X3

0.73

0.28

0.58

0.13

0.70

0.27

0..S4

1 No. 8 iron...... I

X No. 6 copper. . . )

0.17

0.83

0.31

0.67

0.16

0.82

0.31

0 64

0.16

0.80

0.29

0.63

2N0. 6c.c.— 40%.

0.19

0.87

0.33

0.71

0.19

0.87

0.33

0.70

0.17

0.84

0.31

0.68

3 No. dec— 30%.

0.23

0.91

0.36

0.76

0.26

0.91

0.36

0.76

0.20

0.89

0.34

0.73

3 No. 8 iron

0.40

0.97

o.si

0.89

0.37

0.97

0 48

0.88

0.35

0.96

045

0.86

To capacity

o.xo

0.46

0.26

0.46

O.IO

0.46

0.26

0.46

O.IO

0.44

0.26

0.46

2 No. 6 copper

0.14

0.74

0.29

0.60

0.13

0.73

0.39

0.59

O.X3

0.71

0.38

0.58

I No. 8 iron J

1 No. 6 copper. . . )

0.X7

0.84

0.32

0.68

0.17

0.83

0.31

0,67

0.16

0.8k

0.30

0.65

2N6.6C.C.— 40%.

O.X9

0.88

0.33

0.72

0.19

0.87

0.33

0.69

0.18

0.8s

0.33

0.70

a No.4c.c.— 30%.

0.23

0.91

0.37

0.77

0.23

0.91

0.36

0.77

0.21

0.89

0.3S

0.76

a No. 8 iron

0.41

0.97

0.52

0.89

0.37

0.97

0.49

0.88

0.3s

0.96

0.46

0.84

To capacity

O.XI

0.48

0.26

0.48

O.IO

0.48

0.26

0.48

O.II

0.48

0.36

0.4B

a No. 6 copper

0.14

0.75

0.29

0.62

0.14

0.73

0.29

0.60

0.13

0.7a

0.29

0.60

1 No. 8 iron 1

t No. 6 copper. . . f

0.17

0.84

0.32

0.69

0.17

0.84

0.31

0.68

0.16

0.82

0.31

0.67

2 N0.6C.C.— 40%.

o.ao

0.88

0.34

0.73

0.20

0.88

0.34

0.73

0.18

0.85

0.33

0.71

2 N0.6C.C,— 30%.

0.23

0.91

0.38

0.78

0.23

0.91

0.37

0.78

0.21

0.89

O.J6

0.76

2 No. 8 iron

0.41

0.97

0.53

0.89

0.37

0.97

0.49

0.88

0.3S

0.96

0.47

0.87

To capacity

O.II

0.S2

0.27

0.52

O.II

0.52

0.27

0.52

O.IX

o.sa

0.37

0.5a

2 No. 6 copper

0.15

0.77

0.30

0.65

0.14

0.76

0.30

0.65

0.14

0.7S

0.30

0.64

I No. 8 iron 1

X No. 6 copper. . . '

o.x8

0.86

0.33

0.72

0.17

0.85

0.33

0.71

0.17

o.Sa

0.3a

0.70

aNo.6c.c.— 40%.

0.20

0.89

0.36

0.7s

0.30

0.89

0.35

075

0.18

0.86

0.34

0.74

2 N0.6C.C.— 30%.

0.24

0.92

0.39

0.80

0.24

0.92

0.38

0.81

0.22

0.90

0.37

0.78

2 No. 8 iron

0.42 0.97

0.54

0.90

0.38

0.97

0.51

0.89

0.36

0.96

0.48

0.87

1 •

1 ■

I !_ • _^

ex. ^cBfVBT dad.

TRACK CIRCUIT CALCULATIONS.

441

be much greater than would be indicated by the usyal jFonpulae
and tables for non-magnetic conductors. The "skin e^ect"
depends upon the permeability of the rails, which latter fac*
tor is a variable depending on the current density. Dye to
the presence of this variable, the magnitude of the 9)dn effect
is not susceptible to mathematical calculation. The per-
meability factor also obviously influences the magnitude of
the self-inductance and in turn the reactance of the circuit.
Actual measurements have, therefore, had to be resorted to
and Table No. I on the preceding page so detennined gives
the total impedance per 1000 feet of track (both rails includ-
ing bond wires) under various conditions of bondinji^ in com-
mon practice, and for values of current commonly used for
relay energization; these tables have been in use for six or
seven years and have been found to give results sufficiently
accurate for all practical purposes. While the values shown
apply especially to steam road conditions, they may al^ be
safely used on electric road track circuit calculations, since
the presence of propulsion current in the rails will only tend
to decrease the permeability of the rails and in t^ip their
effective resistance and impedance; hence the voltage at the
relay may increase slighdy with heavy propulsion currents
flowing in the rails and any error introduced wi}l be on the
safe side. Table II shows separately the resistance of vari-
ous kinds of bond wires as used in steam road wgrk; on elec-
tric roads the rail is bonded to capacity, or nearly so, fof pro-
pulsion current.

TABLE U.

RESISTANCE OF BONDS TO SIGNAL CURRENTS.
Ohms per 1000 feet of track.

Bonds per Joint

27.5 Ft.
Rails

30 Ft.
Rails

33 Ft.
Rails

2 No. 6 B&S Copper

1 No. 6 B&S Copper &

1 No. 8 BW> Iron

2 No. 6 Copper clad 40 %
2 No. 6 Copper dad 30 %
2 No. 8 BWG iron

0.057

0.098
0.124
0.166
0.348

0.052

0.089
0.112
0.150
0.315

0.048

0.082
0.103
0.138
0.291

Bonds 4 8
f^ches long :
BO allow-
;^ n c e is
rnade for
c o n 4 uct-
ance qf fish
P^a^tes

3* Ballast, Leakage Resistance and Conductance.

The resistance of the leakage path between rails in ohm^ per
1000 feet of track varies with the nature of the ballast, the

442 ALTERNATING CURRENT SIGNALING.

condition of the ties, and the weather ccmditiens. In connec- \

tion with the calculations involving rail impedance as given in |

Tables I and II, the following values for resistance of ballast I

and ties may be used; they are given for ballast cleared away

from the rails:

Ohms
per 1000 ft. of track
Wet Gravel 3 I

Dry Gravel 6

Wet Broken Stone 6

Dry Broken Stone 16

In making track circuit calculations, a leakage resistance
of 6.0 ohms per thousand feet is very commonly used as rep-
resenting the worst condition of well drained broken^ stone
or rock ballast; two ohms per 1000 feet is a low wet wieiather
value for track with gravel ballast. Poorly drained cinder
ballast with old water-soaked ties will generally run as khv as
one ohm per thousand feet. In making the calculationr the
wet weather ballast leakage figure should be used as^ if the
track transformer were designed and track circuit ^idjust-
ments were made on the d^ weather basis, the track telay
might fail to pick up in wet weather. It is, however, advis-
able to make a check calculation on the dry weather basis in
order to determine the variation in voltage on the track relay
from the wet to the dry condition, as in the case of extremely
long track circuits with poor ballast, the relay voltage in dry
weather may be so high that special means may have to be
employed to prevent the relay from being excessively ener-
gized. In track circuit calculations it is generally more con-
venient to represent the ballast leakage factor in terms of
conductance rather than resistance; conductance (expressed
in mhos) is the inverse of resistance (expressed in ohms), and
thus a ballast leakage resistance of 6.0 ohms per thousand feet
corresponds to a ballast conductance of ^ mho per thou-
sand feet.

4. Track Circuit Formulae and Their Derivation.
Given the voltage e and the current / requii*ed at the track
relay terminals, the length of the block, the rail impedance
with its power factor, and the ballast leakage resistance, the
problem which confronts us is the determination of the
power to be fed into the track at the transformer end.

To begin with, due to the impedance drop in the rails

TRACK CIRCUIT CALCULATIONS. 443

caused by the relay current, the ditference of potential be-
tween the rails increases from e at the relay end of the track
circuit to some higher value E at the transformer end; thus,
the ballast leakage current increases as we proceed from the
relay to. the transformer. The ballast leakage current itself
produces a drop in the rails which again increases the voltage
required at the transformer. The fact that the ballast con-
ductance is distributed uniformly throughout the length of
the track circuit rather complicates matters in that the current
in the rails arid the voltage across them from point to point
changes with the varying magnitude of the ballast leakage cur-
rent. I n order to simplify matters, it is sometimes assumed that
the ballast leak is concentrated at the center of the track circuit,
but this is not strictly accurate: evidendy the concentrated
ballast leak is located nearer the transformer end of the track
circuit than the relay end» for it is near the transformer end
that the voltage is highest and the ballast leakage greatest. The
correct determination of the ballast leak is therefore some-
what of an involved process. 1 1 can» however, be determined,
and in fact this method is quite extensively used in Ejigland;
the reader who is interested in this phase of the matter is re-
ferred to a very interesting and complete discussion given in
the January, 1915, issue of the Railway Elngineer of London.

It is evidendy more accurate to consider the ballast con-
ductance as uniformly distributed, and by means of the fol-
lowing simple formulae, originated by Mr. L. V. Lewis and
first presented in the July, 191 1, number of the Signal Engi-
neer, the voltage E and the current I at the transformer end
of the track circuit, as well as their phase relationship, can
easily be calculated. These general equations are:

E= ecosh VZG -}- i J|^ sinh VZG (I)

I = i cosh VZG +e.B sinh -v/ZG (2)

Vi^"

where e and i are the relay voltage and current respectively;
Z is the total impedance of the rails of the track secured by
multiplying the values in Table 1 by the length of the track
circuit in thousands of feet, and G is the total ballast leakage
conductance secured by multiplying the reciprocal of the

444 ALTERNATING CURRENT SIGNALING.

%■! ■ ■ — ■■-■ ■ »■ ■■ I I .1- II.. .I..— i.- ■■ fc ■■ .1 ■— ■^W^— ^^

baJlAst leakage resistance in ohms per thousand feet by the
lens^ of the track circuit in thousands of feet. The terms
cosh and sink (pronounced "cosh" and "shin") are the hyper-
bolic cosine and sine respectively of an imaginary or complex
angle l^presented in this case by the quantity VZG. These
formulae may be reduced to workable form by expanding the
functions into their corresponding infinite series beginning

X^ X* X®

cosh x=I + |_-hj-j+p^+ (3)

sinh x=x+-^+|-^+ py- -}-.... (4)

LL LI IL

wher^ X represents the hjrperbolic angle VZG and the sign |
represents'arithmetical multiplication; for example,! 3 js called
"factorial three" and is equal 1x2x3= 6; likewise,! ^ = I
X 2 X 3 X 4 = 24. Hence

eo.hV2e=1+^ + ^^'?- +^ +...(5)
V 2 24 720

_ -/^ . V(ZG)« ^ V(Z^

sinh V ZG = VZG ^vv^^ ^-v\^i_2^ + ... (6)
Substituting the above values in equations (1 ) and (2)

Reducing and rearreuiging the terms of equation (7) and (8)

E=e + Zi + yGe + -3 ^Zi+^^~Ge+ ... (9)

G G Z G Z G

l = i+Ge+2^Zi+3- Y Ge + -;^ y -^ Zi + . . . (10)

Th6 above equations may be carried out to any number of
termd by carrjdng out the above process, noting that the first
elemeAt of each term of equation (9) is Z, and of equation (1 0)
G, each divided by 1 , 2, 3. 4, etc.» according to the number of
the term in the infinite series, the remaining elements of the
term under consideration being identical with the next pre-
ceding term in the other equation. Sufficient accuracy for all

TRACK CIRCUIT CALCULATIONS. 445

— - - — -

practical purposes will in most cases be secured by calculating
only the first five terms of each series as above shown, the re-
maining terms being generally small enough in value to be
disregarded.

Equations (9) and (10) may also be developed direct from
Ohm's law, stating that E = 1 Z and I = E G, and consid-
eration of the matter on this basis will enable the reader to
grasp fully their physical meaning. To begin Math, the first
two terms e and / of equations (9) and (1 0) are the relay volt-
age and current respectively and as such are knovm. Relay
current / flowing through the rail impedance causes a drop
62= Zi and likewise the relay voltage e impressed acrosa the
rails throughout the length of the track circuit produces a
leakage current '2 ~ ^* ^' ^^^ ^ therefore constitute the
second terms of their respective series. Obviously e^ ^^ Zi
(where i is constant) increases uniformly from the relay to the

transformer and its average value is therefore "t An<i the

Cn G

corresponding baUast leakage current is i^ ^'^^"~J ^»

Z
likewise, it may be shown that «8 ^ 2~ ^' These last quan-
tities thus constitute the third term of the current and volt-
age series respectively.

The development of the next voltage term e^ from i^ pre-
sents some difficulty in that we have no reason for flftwiming

that the average value of /g is '^; as a matter of fact, it is not,

since i g contains the product of the two factors G and Z, vary-
ing with the length of the track circuit, and hence increases
with the square of the distance from the relay. It may be
demonstrated by the calculus that in any equation
of the form y = x° the average value of y between

.1
the limits of y, and o \s—, — ; — ;t of the maximum value of y

^n -f- 1;

Therefore, the average value of /g above is *~|*and the cor^Vls-

,. . . Zig Z G ^

ponding e. m. f. is e^ = -j^ =-^ "o^* •**^ likewise

446 ALTERNATING CURRENT SIGNALING.

G Z
^4^ ~^ ~2 ^^' ^^^ latter values form the fourth terms of the

voltage and current series respectively, and the process may be
carried out until equation (9) and (10) are entirely duplicated.
It should be noted that any term in the current series is de-
rived from the preceding term in the voltage series by multi-
pljring by the conductance G, divided by 1.2, 3, etc., depend-
ing on the number of the term, which is perfectly logical since
it is that preceding voltage which causes the current in question
to flow; conversely, any term in the voltage series is derived
from the preceding term in the current series by multiplying
it by Z, divided by 1,2, 3, etc.

5. Comparison of Center Leak and Distributed Leak
Methods. If the above terms are developed by the centre
leak method, in which the entire ballast conductance is con-
sidered as being concentrated at the centre of the block, we
find that

Z Z G

£=. e-hZi-h^Ge -hy yZi (II)

1 = i+Ge +yZi (12)

The first three tenns of the above formulae are identical with
the corresponding terms of equations {9) and (10) calculated
on the distributed leak basis. The fourth term of equation
(1 1 ) is however 50 per cent, greater in value than the corres-
ponding term of equation (9). The center leak method will
therefore, give sufficiendy accurate results where the track
circuit is short enough in length to permit all terms after the
third being disregarded.

6. Application of Track Circuit Formulae; Exam-
ples. Let us apply formulae (9) and (10) to two of the usual
track circuit arrangements, first, considering a galvanometer
relay on a steam road, and, second, a polyphase relay on an
electric road. Both of these relays are of the two-element'
type and one of them (the galvsinometer) works most eco-
nomically with the currents in its track and local elements in
phase or nearly so, while the other (the polyphase) works best
with its track and local currents in quadrature. These esxam-
ples may therefore be considered as representative; calcula-

TRACK CIRCUIT (lALCULATIONS.

447

II!

ffl-

!•■-.

If.

I r

?i < I I ! I

! I I >

I I I I I I I I

I . . I I

; I I I I I I I • I

Fig. 240. Vector Diagram For a Track Circuit Equipped with a Galvaa-

, ometer Relay.

448 ALTERNATING CURRENT 6IGNALING.

» M ■ I I I I I I II III ■ II ■ II I I I I II

tions for a track circuit employing a single element relay would
of course be made in exacdy the same manner, the calculation
and diagram as used in the case of a two-element relay bong
simply discontinued after the track volts, amperes and power
factor at the transformer are determined for the one winding
used in the case of the single element instrument.

(a) Galvanometer Relay: See vector diagram Fig. 240.
Steam road 100 lb. rails, 33 feet long, bonded with 2-40 per

cent, copper clad wires.
Track circuit 5,000 ft. long, end fed; ballast resistance 6.0 ohms

per 1 ,000 feet.
Relay: track 1 .7 V., 1 .0 A., 0.9 P. F., on 60 cycles;
local 110 V. 0.3 A., 0.4 P. F., on 60 cycles.
Rail impedance Z = 5 x 0.31 = 1.55 at 0.68 P. F. (See
Table 1).

Ballast conductance G= 5x-t^ = 0.83 at 1 .0 P. F.

Relay and transformer leads to track, 1 00 ft. No. 9 each set =

0.08 ohms.
Resistance drop in relay leads = 1 .0 x 0.08 = 0.08 volts.

E= 1.78 -}- 1.55 + 1.14 .+ 0.33 +0.12 +

I = 1.0 + 1.48 + 0.643 + 0.318 + 0.069 +

Volts at rails opposite relay = 1 .78 obtained from Fig.
240 ; it is the vectorial sum of the relay voltage e = 1 .7 cuid
the lead drop 0.08 volts, the latter being in phase with
and hence parallel with the current vector i = 1 .0 drawn
at an angle whose P. F. = 0.9 lagging behind the relay
volts e= 1 .7.
In plotting the various leakage currents and their correspond-
ing drops in Fig 240 it will be remembered that each term in the
voltage series is obtained by multiplication of the preceding
terms in the current series by Z; the power factor of Z is 0.68
and hence each term of the voltage series is laid off at a lead
angle whose P. F.=cos 8= 0.68 using the preceding term of
the current series as a base line. The ballast conductance G
is, of course, non-inductive and its P. F. = 1 ; hence each term
in the current series is parallel with the preceding term in
the voltage series which produces it. ^

Following the above method the final current at the trans-
former end of the track circuit will be found to be I == 3.22

TRACK CIRCUIT CALCULATIONS. 449

amps; it is simply the vectorial sum of the relay current and
the various ballast leakage currents laid off with due atten-
tion to phase relationship. Likewise the final voltage at the
rails at the transformer end of the track circuit is E = 4.3
volts, for it is again the vectorial sum of the relay voltage and
the various rail drops caused by the ballast leakage currents.

To prevent the flow of an injurious short circuit current
flowing through the transformer secondary with a train in
the block* it is necessary to insert some current limiting de-
vice between the transformer and the track and for this pur-
pose we will select the impedance coil shown in Fig, 137,
page 225, having a power factor of 0.2. The feed current
of 3.22 amps, flowing through the leads between the trans-
former and the track gives a drop of 3.22 x .08 = 0.26 volts»
laid otf parallel to the. current since the leads are non-in-
ductive. As will presently be explained, enough impedance
ought to be inserted between the transformer and the track to
make the v<^tage at the transformer secondary about twice
that at the rails. The impedance drop vector is laid oS at a
P. F. = 0.2 with the current and is made long enough so that
the transformer secondary voltage will meet the impedance
drop vector at a point where Ex = 2 x 4.5 = 9.0 volts.

The relay local current has a lag angle whose P. F. = 0.4,
and hence it is laid otf at a P. F. of 0.4 with the transformer
secondary vcJtage Ex* for while the transformer which supplies
Ex is not the same one as feeds the relay local, the transformer
feeding the local is connected to the same transmission and
hence its voltage is in phase with Ex*

The relay local current thus laid off will be found to be
nearly in phase with the track element current. From Chap-
ter IV it will be remembered that in the case of relays of the
galvanometer type, maximum power economy is secured with
the track and local elements in phase, and it was in order to
secure this ideal relationship that an impedance coil was used
between the transformer and the track; if a resistance having a
unity power factor had been employed instead, the entire drop
between the transformer and the track would have been in
phase with the current vector I = 3.22 and the vector Ex
would have been swung around in a clockwise direction
through a large angle; the local current vector laid otf thf

450 ALTERNATING CURRENT SIGNAUNa

from at a P. F. = 0.4 would then have been away out of

phase with the track current vector and hence the relay

would not have operated economically since the voltage for

, the track at the relay would have had to be increased until

that component of the track current in phase with the local

current were equal to 1 .0 ampere as we started otf with.

Scaling the cuigle between the transformer voltage E^ and

the current* we find it to be such that the cosine or P. F. =

0.62; hence, the total power with the block unoccupied is

Ex I cos 6=9x3.22x0.62= I8watts. With a train on the track

circuit opposite the transformer, the current flowing will be

equal to the transformer voltage £t divided by the vectorial

sum of the inserted impedance and the resistance of the

transformer track leads. The drop in this part of the circuit

as scaled from the diagrams is found to be 5.5 volts and this

is due to a current I = 3.22 amps.; hence the combined value

Et 5.5
of the impedcuice and leads is Z = ~jr = ITj^ ^^ ' -^ ' ohms.

With a train on the track circuit as above there will be only
1.71 ohms in series with the transformer secondary, and, neg-
lecting the resistance of the wheels and eudes of the train
which is negligible, the short circuit current flowing will be

9.0
r-=T = 5.26 amperes, th^ corresponding power factor being

0.26 as scaled from the diagram, this being simi^y the power
factor of the impedance and the resistance of the track leads
in series. The total power with the block occupied is. there-
fore, 9 X 5.26 X 0.26 = 12.3 watts. It is thus seen that the
power with the block occupied is less than when the block is
clear; this arises from the fact that the short circuit current
with the block occupied is almost in quadrature with the
transformer voltage due to the phase displacement produced
by the impedance coil.

Polyphase Relay; see vector diagram Fig. 241.
Electric road, 70 lb. rails, 33 ft. long, bonded to capacity.
Double rail end fed track circuit, 8.000 ft. long.
Relay, track 0.15 V., 0.25 A., 0.65 P. F. on 25 cycles:

local 12 V., 0.20 A.. 0.4 P. F. on 25 cycles.
Z on 25 cycles = 8 x 0.1 1 = 0.88 at 0.52 P. F.
G»= 8 y.}^^ 2mho8forbaUastleakageof 4per 1,000ft.

TRACK CIRCUIT CALCULATIONS.

451

_ . I < ' T I ~i ' i f I I • I ; ' i 1 '

e^ I I I I I , I I , I I I I I I I « I

J. I I t I I I * I • I I i • I I I

# t I I I I I I I I I I I I '. I I I '

1 flop J

fVW\

I I I
I • I
I I I

lEZ

R^u^^ilX

0.02 V. Leads

-0.021

Fig. 241. Vector Diagram For a Track Circuit Elquipped With a Poly^

phase Relay.

452 ALTERNATING CURRENT SIGNALING.

Impedance bonds, 500 amperes per rail with unbalancing ca-
pacity of 150 amp.» impedance 0.31 ohms at 0.15 P. F.
Relay and transformer leads 1 00 ft. No. 9 wire = 0.08 ohms.
Drop in relay leads = 0.25 x 0.08 = 0.02 volts.
Volts opposite relay = 0. 1 6 scsded from diagram.

Bond current at relay end = ^ ^. = 0.52 amps.

Total current at relay end = 0.75 amp. from diagram.
E = 0.16 + 0.66 + 0.14 4- 0.196 + 0.021 + 0.017
I = 0.75 + 0.32 + 0.66 + 0.093 + 0.095 + 0.008

Referring to Fig. 241 , the relay voltage 0. 1 5 V. and the cur-
rent 0.25 A. are laid off at a P. F. = 0.65 as before, and tak-
ing into account the drop in the leads of 0.02 V., laid oS paral-
lel to the relay current, the voltage at the relay end of the
track circuit is found to be e = 0.16. At 0.16 volt the bond
A takes 0.52 amps, and this current is laid off lagging at an
angle corresponding to 0.15 P. F. with the track voltage e.
The total current at the relay end of the track circuit is the
vectorial sum of the relay current and the bond current and
scales 0.75 amps. Applying equations (9) and (10) and lay-
ing oS the various ballast leakage currents and voltages list-
ed above in exactly the same way as in the case of the gal-
vanometer relay diagram. Fig, 240, the current I = 1 .5 A.
and the voltage E = 1 .0 V. is found at the transformer end
of the block. The bond B at the transformer end of the block

1.0
takes at 1 .0 vcJt zriri = 3.23 amps, and this current is laid

off at a P. F. = 0. 1 5 with the corresponding voltage E and
the total current fed into the track scales 4.45 A., being the
vectorial sum of the bond current 3.23 A. and the track cur-
rent I = 1.5 A.; employing a resistance between the trans-
former and the track, the corresponding drop is laid off in
phase with and parallel with the total current and with a
transformer voltage of twice the track voltage, the final volt-
age at the transformer secondary E^r = 2.0 is obtained. The

drop in the leads and resistance scales 1 .4 volts and the cor-

1.4
responding total resistance is , , - = 0.315 ohms.

On laying off the vector for the current in the local element
of the relay at a P. F. = 0.4 with the transformer voltage Bp

TRACK CIRCUIT CALCULATIONS. 453

it will be noted that the local current is considerably out of
phase with the track element current, though not a full 90^
for quadrature relationship as required for the most econom-
ical operation of the polyphase type as explained in Chapter
IV. In fact, if we lay off a line at right angles to the track
element current as ^own at the left of the diagram, and pro-

100
ject on it the local current, we find that only .y.' or 0.8 of

the local current is in quadrature with the track current so
that we must compensate for this imperfect phase displace-
ment by increasing the transformer voltage accordingly, the
current values for the two elements of the relay as given in
the list above being based on a pure quadrature relationship.
To make the quadrature component of the track current a
full 0.25 A. which we started out with in lajring out the dia-
gram, we increase the transformer voltage in the proportion of

track increases in corresponding ratio with the voltage, and;

125
thence, the final feed current I is ~77j^ x 4.45 = 5.56 ampfi.

The drop across the resistance and leads scaling 1 .4 is likewise

125
increased to -^ x 1 .4 = 1 .75, and the corresponding value

1.75
of the resistance is TTr" =.315 ohms.

J.JO

. With the block clear the total power is E<r Iq cos >:= 2.5 x
5.56 X 0.88 =>: 12.2 watts, the power factor of 0.88 being the
cosine of the angle between Iq and E<r as scaled from the dia-
gram. With a train on the circuit opposite the transformer,
the maximum current is equal to the transformer volts divided
by the total resistance between transformer and the track and

.2.5
is ~^Tc ^ T*^^ amps, at 1 .0 P. F. since the resistance is non-
inductive. The power with the block thus occupied is
2.5 X 7.94 X 1 .0 = 19.8 watts.

It will now be apparent why a resistance was employed be-
tween the transformer and the track, for if sin impedance had
been used instead, the local current vector would have been
nearly in phase with the track current vector and the relay

454 ALTERNATING CURRENT SIGNALING.

would hardly have picked up even with several times its nor-
mal current, simply due to the imperfect phase displacement;
7. The Train Shunt. In general, alternating current
track relays have a much lower internal impedance than the
ordinary track relays used in direct current practice; for ex-
ample, the galvanometer relay which we considered in con-

E 1.7
nection with Fig. 24G has an impedance of Z = "^ ~ Va ~

1.7 ohms, while the polyphase relay discussed in connection
with Fig. 241 has sin impedance of ^ ^- = 0.6 ohms as com-
pared to the resistance of 4.0 ohms of the standard direct cur-
rent instruments. Since, with two circuits in parallel, as in
the case of the track relay and the car wheels across the rails,
the current in each circuit is inversely proportional to the re-
sistance of that circuit, it follows that with a train shunt of
given resistance the alternating current track relay will take
a larger proportion of the current than would be the case with
a direct current relay; hence the train shunt is not so effective
in the former case.

The value of the train shunt in ohms is of course equal to
the impedance of the axles added vectorially to the ohmic
contact resistance between rails and car wheels. The im-
pedance of the wheel and axle part of the shunt circuit is negli-
gible, and hence the react€uice factor in the circuit may also be '
neglected. It is also true that in the case of the heavy rolling
stock employed in steam and electric trunk line service, the
wheel-rail contact resistance may likewise be considered as in-
significant. Table 111 below was compiled from a series of tests
made on rails with a clean bearing surface in which a single pair
of wheels and their axle was submitted to various loads. 1 1 will
be noted that the total resistance of the shunt thus formed
is practically independent of the loading; while the total
shunt resistance is extremely low in all cases, it is to be noted
that, as might be expected, the total apparent resistance in-
creases with the frequency. Compared to any of these shunt
resistances the impedance of the relays above given is so enor-
mously high that the shunt may be considered as practically
perfecL

TRACK CIRCUIT CALCULATIONS.

455

TABLE IlL

Contact Sitrface of Wheels and Rails Clean Metal.

Total

Apparent
Ohmic

Fre-

No.

Lbs.

Amps.
Axle

Volts

Res.

quency
Cycles

Weight

Across

Between

Test

on Track

Current

Bails

Rails via

Wheels
and^xle

18,700

185

0.133

.0007

23.052

175

0.13

.0007

27.404

180

0.134

.0007

36.108

180

0.14

.0008

18.700

112.5

0.12

.001*

27.404

112.5

0.114

.001

36,108

112.5

0.11

.00097

18.700

.022

.0004

d.c.

27,404

.021

.00037

36,108

.018

.00033

♦Note— 2' 9" of axle gave drop of .048 volts. From this point
(on either side) to rail average drop 0.35 volts.

It is only when rusty or dirty rail surfaces are encountered
that the resistance of the train shunt becomes significant and
this statement applies equally well to direct current track cir-
cuits; every signal man is familiar with the occasional dif-
ficulties experienced on heavily sanded track. Table IV indi-
cates what the surface contact resistance may amount to, the
tests having been made on a four wheel trudc loaded so that
th^ total weight on the rails was 40,900 lbs.

TABLE IV.

Clean Rails

Rusty Rails

25 Cycles

60 Cycles

25 Cycles

60 Cycles

Total amps, through

axles
Volts across rails
Train shunt in ohms
1

220
0.232
0.00105

180
0.1
0.00055

70
0.82
0.0117

126
0.37
0.003

On steam and electric trunk lines where the rolling stock is
generally heavy and the train movements are frequent enough
' to keep the rails clean, it may be safely assumed that the train
shunt resistance is so extremely low as to be negligible. On
some of the interurban trolley lines, however, where light
single car trains are operated and movements are not frequent

456 ALTERNATING CURRENT SIGNALING.

* IM MM. —L.^J-LJH 1»» I -■■-■■■■ I ■ IBJ I I I _ i I I

enough to keep the rails bright, the value of the train shunt
must be taken into consideration; in such cases, it has been
found to run much higher than the values in Table IV and since
the relay ought to be shunted out to a point at least 50 per
cent, below its minimum shunt point, it is often customary
to make electric road track circuit shunt calculations with a

train ^unt value of 0.064 ohms. In those cases on electric
roads where it is suspected that the train shunt may be of
comparatively high resistance due to light rolling stock and
rusty rails resulting from infrequent train service, it is there-
fore generally advisable to check the track circuit calculations
as described below in order to be certain that the relay will be

shunted open with a train in the block.

8. Methods of Controlling Track Circuit Sensitiveness.

In the first place, the train shunt is least effective when the
train is opposite the relay, for at that time the entire rail im-
pedance will be in circuit between the train shunt and the track
transformer with the result that the track feed current and
the consequent drop in the resistance or impedance between
the tran^ormer and the track will be less thai|<^)ttd^ the train
opposite the transformer; then, since the voi|(ige at the rails
opposite the transformer is the vectorial t^tference between
the transformer voltage and the drop in the f^sistanee or re-
actance inserted between the transformer and the track, it fol-
lows that with the train opposite the relay, the voltage at the
track opposite the transformer and in turn that opposite the
relay will be greatest when the train is at the rday end of the
track circuit. Since this latter is the worst condition en-
countered, calculations to improve the effectiveness of the
track circuit should be made on this basis.

What we desire to do is to reduce to the lowest point pos-
sible the voltage at the relay with a train in the block, and it
will be immediately apparent from the above discussion that
we have in the impedance or resistance (as the case may be)
inserted between the transformer and the track a very effec-
tive means of controlling the voltage at the raild opposite the
transformer, since, as this voltage decreases so also will the
voltage at the relay decrease. Hence, if we used an imped-
ance or resistance of high value the short circuit current with
a train on the block will cause a correspondingly heavy drop

TRACK CIRCUIT CALCULATIONS. 457

between the transfonner and the track ftnd as a result the
track voltage opposite both transformer and rday will be low.
It is customary to use sufficiently high impedance or resist-
ance so that with the block clear the voltage at the track op-
posite the transformer will be about one-half that at the trans-
former secondary, and it was with the train shunt in mind
that these values were employed in connection with Figs. 240
and 24 1 ; with such an adjustment the track voltage will general-
ly fall to a perfectly safe figure when a train comes on the track
cdrcuit. Inserting impedance or resistance to give a trans-
former voltage greater than twice the track voltage will rarely
be justified since after the relay is once shunted out with a large
margin of safety any further increase in inserted impedance or
resistance will only result in a useless waste of power.

' With the aid of the vector diagrams shown in Figs. 240 and
241, it is not a difficult matter to ascertain whether the in-
serted impedance or resistance, determined on the basis of
the transformer volts being twice the track volts with the
block occupied, will insure the track relay being open with a
train opposite it. It is assumed of course that all the track
circuit constants are known, including the shunting point as
"well as the normal operating point of the relay. With a train
shunt of given value across the rails at the relay, use the nor-
mal operating voltage of the relay plus the dropui the track
leads a« the first term e of equation (9), and considering the
train shunt as an impedance bond of unity power factor, con-
struct a diagram like Fig. 241, leaving the propulsion bonds
out if a steam road track circuit is being investigated; in the
case of an electric road circuit, the train shunt will simply
constitute an extra bond at the relay end in multiple with the
propulsion bond. The vector diagram thus obtained will of
course indicate a . transformer voltage considerably greater
than what is actually existent as determined from the calcu-
lation with the block clear. Calling this hypothetical trans-
former voltage Ets cind the actual existent transformer vent-
age Bxf the volts e at the relay end of the block must be re-

duced in the proportion of ^ — : in turn the relay voltage and
ciirxcat wriU be decreased in like ratio and if with this raduc*

458

ALTERNATING CURRENT SIGNALING.

tion it is found that the relay current is below the shunting
point of the instrument, the impedance or resistance chosen
for the *'bl6ck clear" condition may be considered as satisfac-
tory. If the reduction is not sufficient, the impedance or re-
sistance inserted between the transformer and the track will
have to be arbitrarily increased until the calculations prove
that the relay is effectively shunted.

9. Power Factor Triangle. In laying out vector track
circuit dis^rams such as those shown in Figs. 240 and 241 , the
value of the various angles are given by the calculations in
terms of their cosines, these being the power factors of the

corresponding
angles. The
phase spacing of
vectors is, there-
fore, much more
easily ejected
through the use
of a triangle
marked off in
cosines, such as
that shown in
Fig. 242; than
through the em-
ployment of a
protractor indi-
^ eating degrees.

Fig. t4Z.

Power Factor Triangle For Constructing
Track Circuit Vector Diagram*.

skicein the lat-
ter case the
angles corre- \.
sponding to the cosine would have to be locked up in a table.
A t]»n^>arent triangle should be used as it is often niecesitary -.
to uae^it upsidedown; the lines 0. 1 to 0.7, as drawn from vertex
A ace- laid oft with a protractor at angles with base line B- C •
corre^pnding to cosines of 0.1 to 0.7 as given in the tables at
the backof this book; theiines-O.d to 0.99 as drawn ^m •
verte?e; S^ are laid otf from base line B C likewise at- angles cor-
responding to cosines of 0.8 to 0.99. Considerable care
should-be exercised in using the triangle at 6rst, especially -
when reversing it, as otherwise one may be using the com-
plemeafr of the angle instead of tko angle itself. - - ^'

CHAPTER XIV.

TABLES AND DATA

CHAPTER XIV

TABLES AND DATA

WIRE AND SHEET METAL GAGES

1. Wire Gages; Kinds and Applications. Wires of a
diameter less than ^ inch are usually specified according to
certain arbitrary scales called gages; the gage number of a
solid wire refers to the cross section of the wire perpendicular
to its length: the gage number of a stranded wire or cable
refers to the total cross section of the wires composing it. re-
gardless of the pitch of the spiraling. Wires larger than \
inch in diameter are generally described in terjns of their
cross sectional area in circular mils (abbreviated c. m.) a cir-
cular mil being the area of a circle 1 mil (0.001 ") in diameter
and the circular mil area of any wire is equal to its diameter
in mils squared; thus a wire of 0.100" diameter has a circular
mil area of 1 0,000 c. m.

The principal gages and their uses are as follows:

Brown & Sharpe (B. & S.) or American Wire Gage
(A. W. G.)< Tliis gage is the standard in this country
for the designation of copper, aluminum and resistance
alloy wires. The diameters of wires having successive

numbers are in the ratio of ^V'92or 1 . 1 225 approxi-
mately.

A No. 10 B. & S. copper wire has the following ap-
proximate characteristics:

Ohms per 1000 feet 1

Area in cm 10,000

Weight in pounds per 1000 ft 32

A No. 1 0 B. & S. aluminum wire has the following ap-
proximate characteristics:

Ohms per 1000 feet 1.6

Area in cm 1 0.000

Weight in pounds per 1000 ft 9.5

Birmingham (B. W. G.) or Stubs Wire Gage.
This gage is generally used for the designation of galvan-
ized iron and steel wire; it is sometimes referred to as the
Stubs' Gage, but must not be confused with Stubs' Steel
Wire Gage.

462 ALTERNATING CURRENT SIGNALING.

- ■ ■ - '

United States Steel Wire Gage. This gage is ire-
quently employed in this country for the designation of
steel and iron wire — telephone and telegraph wires for
example. It is also sometimes known as the ''Washburn
and Moen," "Roebling" and "American Steel & Wire
Co." Gage.

British Standard Wire Gage. Tliis gage» usually
called the Standard Wire Gage (S. W. G.) also is known
as the "New British Standard*' (N. B. S.)» the English
Lfgal Standard, or Imperial Wire Gage; it is the legal
standard in Great Britain for all wires.

London Gage. Tliis gage is also sometimes known as
the "Old" Elnglish Wire Gage and is frequently used in
connection with brass wires.

Stubs Steel Wire Gage. Tliis gage is sometimes used
for designating drill rod sizes; the Brown and Sharp Twist
Drill gage is however in most general use for. this purpose.
See Page 480.

Old English Wire Gage. This is occasionally used
for designating brass wire.
2. Sheet Metal Gages.

Brown & Sharpe Gage. This gage, the same as the
wire gage of the same name, is generally used in specify-
ing the thickness of sheet copper, brass and German
silver.

United States Standard Gage. This gage, stand-
ardized in this country by act of Congress, is quite gen-
erally used for the designation of sheet iron and steel.

Decimal Gage. This gsige designates the thickness
of sheet iron or steel in mils or thousandths of an inch.
It has been adopted by the Association of American Steel
Manufacturers, The American Railway Master Mechan-
ics Association, and by the principal railroads in this
country and Canada. It obviously has much to recom-
mend it and is coming into general use for the designa-
tion of all iron and steel sheets and plates.

ENAMELED COPPER WIRE. *

This is a wire insulated with a hard, tough and elastic coat-
ing of special varnish laid and baked on in a series of layers.

TABLES AND DATA.

463

The insulation is moisture proof and will successfully with-
stand temperatures that would completely ruin silk or cotton
insulations. The insulatibn thickness is about one-fourth of
that of single silk in very small wires while for No. 22 B. & S.
or larger the thickness is about the same as that of single silk;
furthermore the dielectric strength of the enamel is about four
times that of an equal thickness of silk or cotton. For these
reasons enameled wire is being used to an even increasing
extent. The table below applies to wire made by the
General Electric Co., and meeting R. S. A. specifications:
it will be i^ted that in many cases decimal sizes, lying be-
tween standard B. & S. gage numbers, are available.

ENAMELED WIRE.

Bare

B. &S.

Gage

Diam.

Wire

G. E. Std.

Max.

diam.

ins. wire

Turns

per

sq. inch

Ohms per
cubic inch

Pounds

per
cu. inch

14
15

.064
.061
.057

.067
.064
.060

223
244
278

.0485
.0578
.0753

.235

.2294

.2275

.054
.051
.049

.057

.0535

.0515

308
349
376

.0934
.1181
.1382

.2274
.2284
.2276

17
18

.045
.042
.040

..0475
.0445
.0425

443
505
552

.1936
.2523
.3046

.2272
.2247
.2231

19
20

.038
.036
.032

.040
.038
.034

625
692
864

.3816
.4982
.7452

.2267
.2258
.2232

21
22

.030

.0285

.0255

.032

.0305

.0275

975
1075
1320

.9569
1 . 1690
1 . 7930

.2211
.2204
.2167

23
24
25

.0226

.020

.018

.024
.022
.020

1753
2066
2500

2 . 9243
4 . 5563
6.8114

.2106
.2081
.2046

26
27
28

.016
.014
.0126

.0175
.0155
.0140

3264
4160
5102

11.258
18.759
28.365

.2111
.2061
.2044

29
30
31

.011
.010
.009

.0123
.0112
.0102

6612
7832
9612

48.251

69.186

104.771

.2022
.1978
.1962

32
33
34

.008
.007
.0063

.0092
.0082
.0072

11815
14872
17768

163.050
267 . 937
395.345

.1920
.1847
.1777

35
36

.00560
.0050

.0063
.0056

25195
31887

709.454
1126.037

.1995
.2019

464

ALTERNATING CURRENT SIGNALING.

WIRE AND SHEET METAL GAGES COMPARED.
DIAMETERS IN DECIMALS OF AN INCH.

"«&

g^ .

§ i

i§

•

i.s

S B V

III

6 is

•22 y^
•St 52

- 2

000000

46875

000000

00000

.45

4.375

00000

0000

.46

.454

..39.38

.40625

0000

000

.40904

.425

..3625

.36

.37S

000

.3648

.38

.3.310

..33

34375

.32486

.34

..3065

.305

3125

.2893

.2830

.285

.227

.28125

.2J^763

.284

.2625

.265

.219

.265625

.22942

.259

.2437

.245

.212

.25

.20431

.238

.2253

.225

.207

.234375

.18194

.22

.2070

.205

.204

.21875

.16202

.203

.1920

.19.

.201

.203125

.14428

.18

.1770

.175

.199

.1875

.12849

.165

.1620

.16

.197

.171875

.11443

.148

-.1483

.145

.194

.15625

.10189

.134

.1.350

.13

.191

.140625

.090742

.12

.1205

.1175

.188

.125

.080808

.109

.10.55

.105

J85

.109375

.071061

.095

.0915

.0925

.182

.09375

.064084

.083

.0800

.08

.180

.078125

.057068

.072

.0720

.07

.178

.0703125

.05082

.065

.0625

.061

.175

.0625

.045257

.058

.0.540

.0.525

.172

.0.5625

.040303

.049

.0475

.045

.168

.05

.03589

.042

.0410

.04

.164

.0457.5.

.031901

.035

.0348

.035

.161

.0375

.028402

.032

.03175

.031 .

.1.57

.0.34375

.02.5347

.028

.0286

.028

.155

.03125

.022571

.025

.0258

.025

.153

.028125-

.0201

.022

.0230

.0225

.1.51

.025

.0179

.02

.0204

.02

.148

.021875

.01594

.018

.0181

.018

.146

.01875

.014195

.016

.0173

.017

.1^3

.0171875

.012641

.014

.0162

.016

.139

.015625

.011257

.013

.0150

.015

.134

.0140625

.010025

.012

.0140

.014

.127

.0125*

TABLES AND DATA.

465

U. S. STANDARD GAGE.
FOR SHEET AND PLATE, IRON AND

No. of

ApprozunAte

thickness, in

decimal parts

of an inch

Approximate
thickness in
millimeters

Weight per

square foot

in pounds

avoirdupois

Weight per .
square meter
in kilograms

0.5000
0.4687
^4375

12.7000
11.9062
IX.X125

20.00

X8.75
X7.50

97.6s
91 SS
85.44

000000-
00000

0000

000

0.4062-
0.3750
0.3437

10.3187
9 5250
8.7312

16.25
15.00

13. 75

79.33
73.24
67.13

0.312s

0.2812
0.2656

79375
7.1437
6.7469

12.50
11.25
10. 62

61.03
S4.93
51.88

4
5

0.2500
0.2344
0.2187

6.3500

5 9531
5. 5562

10.00
9-37S
8.750

48.82

45.77
42.72

7
8

0.2031
0.1875
0.1719

5.1594
4.7625
4.3656

8. 125
7.S00
6.87s

39.67
36.62
3357

0. 1562
0.1406.
0.1250

39687
3.5719
3. 1750

6.250

5.6^5
5.000

30.52
27.46
24.41

12
13
k4

0.1094

0.0937
0.07812

2.7781
2.3812
1.9844

4375
3.750
3.125

21.36
18.31
15.26

IS
X6

0.07031
0.06250
0.05625

1.7859
1.5875
1.4287

2.8X2

2.500
2.250

13.73
12.21

10.99

19
ao

0.05000

0.0437s
0.03750

1.2700

I.III2
0.9525

2.000
1.750
1.500

9.76s
8.544
7.324'

31
22
83

0.03437
0.0312s
0; 02812

0.8731
0.7937
0.7144

I.37S
X.250
X.X25

6.7X3
6.103

S.490

24
2S

0.02500
0.02187
0.0187s

0.6350
0.5556
0.4762

r.ooo
0.87s
0.750

4.882
4.272
3.662

27
28

O.01719
0.01562
0^01406

0.4366

.0.3969
0.3572

0.687
0.625
0.5625

3.357
3.052
2.746

30
31
32

0.01250
0.01094
0.01016

6.317s
0.2778
0.2580

0.5000

0.4375
0.4062

2.441
2.136
X.983

3^
34

0.00937s
0.008594

0.2381
0.2183

0.3750
0.3437

X.83X
1.678

0.007031

O.X786
O.IS87

o.2axa
A^asoo

1.373

i.nt

466

ALTERNATING CURRENT SIGNALINa

STANDARD DECIMAL GAGE.
FOR SHEET AND PLATE, IRON AND STEEL.

(ige in indies

Approximates
' millimeten

Weights per square foot in pounds
avoirdupois

Iron,

Basis: 48c

pounds per cubic

foot

Steel,

Basis: 489.6

pounds per cubic

foot

o.ooi
0.004
0.006

0.0508
0.1016
0.1524

0.08
0.16
0.24

0.081^
0.1632
0.2448

0.008

o.oiov

o.oif

0.2032
0.2540
0.3048

0.32
0.40
0.48

0.3264
0.40B0

0.4896

0.014
0.016 •
0.018

0:3556
0.4064
0.4S72

0.56
0.64
0.72

0.5712
0.6538
0.7344

0.020

e.<D22

0.025

0.5080
0.5588
0.6350

0.80
0.88
1. 00

0.8160
0.8976
Z.0200

0.028
0.032
0.036.

0.7112
0.8128
0.9144

1. 12
1.28
1.44

1.1424
1.3056
1.4688

0.040^

0.04s;

0.050

I. 0160
X.I430
1.2700

1.60
1.80
2.00

Z.632O.

1.8360

2.0400

o.osi
0.060
O.P65

1.3970
1.5240
1.6510

2.20
2.40
2.60

2.2440
2.4480
2.6520

0.070

0.07s

' 0.080

1.7780
1.9050
2.0320

2.80
3.00
3.20

2.8560
3.0600
3.2640

0.085
0.090

0.09s

2.1590
2.2860
2.4130

3.40
3.60
3.80.

3.4680
3.6720
3.8760

O.IOO
O.IIO

0.125

2.5400
2.7940
3.1750

4.00
4.40
5.00

4.0800
4.4880
5.1000

0.X3S
ojso
0.165

3.4290
^.8100
4.1910

S.40
6.00
6.60

5.5080
6.1200

6.7320

0.180

0.200
0.220

4.5720
5.0800
S.5880

7.20
8.00
8.80

7.3440
8.1600

8.9760

0.240

0.2SO

6.0960
6.«soo

9.60
10.00

9.7920

lo.aooo

TABLES AND DATA.

467

FOR

BROWN & SHARP GAGE.
SHEET COPPER AND BRASS.

B.ftS.
Gage No.

inchet

Weight, pounds per sq. ft. 1

Copper

Bran

000
00

0.4600
0.4096
0.3648

20.84
18,56
16.53

19.69
17.53
15. 6z

0.3249
0.2893
0.2576

14.72
13. IX
■11.67

13.90
J2.38
XI. 03

3
4

0.2294

0.2043
0.1819

10.39
9.26
8:24

9.82

'8.74

7.7?

7
8

0.1620

O.I443
0.1285

7.34
6.54
5. 82

6.93
6.Z8'
5*50

10
IZ

0.1144
0. IO19

0.09074

5.18
4.62
4- II

4.90
4.36
3.88

12
13
14

0.08081
0.O7i9(S
0.06408

3.66

'3.26

2.90

3.46
3.08
.2.74

IS
i6

0.05707
0.05082
0.04526

2.59
2.30

2.05

2.44
2.18

1.94

19
30

0.04030 •

0.03589

o!o3Z96

1.83
1.63
Z.45

1.73
1.54
1.38

21
22
23

0.02846

0.02S3S

0.02257

1.29
1.15
Z.02

i.22
1.08
0.966

0.020ZO
0.01790
0.01594

0.911
0.811
0.722

o.8(5o
0.766
0.682

27
28

0.01420
0.01264
0.01Z26

0.643
0.573
0.510

0.608
0.541
0.482

30
31 '
32

0»0Z003

0.008928
0.007950

0.454
0.404
0.360

0.429
0.382
0.340

33
34
36

0.007080
0.006304
0.005000

0.32Z

0.286
0.226

•

0.303
0.270
0.214

38
40

0.003965
0.003145

0.180
0.142

0.170
0.I3S

468

ALTERNATING CURRENT SIGNALING.

RESISTANCE OF COPPER WIRE
B. & S. GAGE— SOFT DRAWN— 100% CONDUCTIVITY

The resistance of hard drawn copper line wire is about 1 .026 times the
values shown below; see table page 336 for hard drawn wire.

•

0000

000

Diam-
eter in
mils,

Crosis-sectioa

Resistance at
20** C. or 68* F.*

Weight in
pounds

Feet per
pmmd

•

Circular
mils

Square
inches

Ohms per
1000 feet

Ohms
per mile

per
1000 feet

per
mile

460.0
409.6
364.8

211,600
167,800
133.100

0.16G2
0.1318
0.1045

0.04901
0.06180
0.07793

0.2S9

0.326
0.411

640.5
S07.9
402.8

3380
2680
2130

X.561
X.968
3.482

o
I

324-9
289.3
2S7.6

105,500
83.690
66,370

0.08289

0.06573
0.05213

0.09827

0.1239

0.1563

0.519
0.654
0.825

319.S
253.3
200.9

1680
1340
1060

3x30
3.947
4.977

229.4
204.3
181. 9

52,640
41.740
33,100

0.04134
0.03278
0.02600

0.1970
0.2485
0.3133

1.04

1. 31
1.65

•

159.3
126.4

100.2-

841
667
529

6.276

7.9M
99«6

7
8

162.0

144.3;

128.5.

26.250
20.820
16.S10

0.02062
0.01635
0.01297

0.39SI
0.4982
0.6282

2.09
2.63

3.32

79.46
63.02
45,.9«

420

333
264

X2.58

xs.a?

20.01

10
12
14

toi.9
80.81
64.08

10,380
6.SJ0
4.107

0.00615s
0.005129
0.003225

0.9989
X.588

2.525

S.28
8.38
13.3

31.43
19.77
12.43

166
104
63.3

31.82

SO. 59
80.44

IS
IC

S7.07
50.82
45.26

3.257
2,583
2,048

0.002558
0.002028
0.001609

3.184
4.015
5. 064

x6.8
21.2
26.7

9.858
7.818
6.200

52.0
41.3
32.7

10X.4
127.9
16X.3

40.30
35.89
31.96

1,624
1.288
1,022

0.001276
0.001012
0.0008023

6.385
8. 051
10.15

33.7
42.5
53.6

4.917
3.899
3.092

26.0.
20.6
x6.3

aoi.4
323.4

21
22
23

28.46
25.35

22TS7

810.1
O42.4
S09S-

0.0006363
0.0005046
0.0004002

12.80

16.14
20.36

67.6
85.2
108

2.452
1.94s
1.542

12.9
X0.3
8.X4

407.8
514.2
648.4

24
25
26

20.10

17.90

15 94

404.0
320.4
254. 1

0.0003173

0.0002517
0.0001996

25.67
32.37
40.82

.135
171
216

1.223

0.9699

0.7692

6.46
5.12
4.06

817.7
1,031
1,300

27
28

14.20
12.64
XI. 26

201.5
159.8
126.7

0.0001583
0. 0001255
0.000099S3

SI. 46
64.90
81.84

272
343
432

0.6100

"0.4837
0.3836

3.22
2.55
2.03

1.639
2,067
2,607

30
31

10.03
8.928
7 950

100.5
79.70
63.21

0.00007894
0.000062O0
0.00004964

103.2
130. 1
164. 1

545
687
866

0.3042
0.2413
0.1913

X.61
•X.27
X.OI

3.287
4.14s
5,227

33
34
3S

7.080
6.J05
5. 615

50.13
39-75
31.52

O.000039J7
0.00003122
0.00002476

206.9
260.9
329.0

1090
1380
1740

0.IS17
0.1203

0.09542

0.814
0.63s
0.504

6.591

8.310

10,480

36
38

S.ooo
3.965
3 145

25.00
IS. 72
9.888

0.00001964

0.00001235

0.000007766

414.8
659-6
1049

2190
3480
S540

0.07568
0.04759
0.02993

0.460
0.251
0.158

13:210
21,010
33,410

*Let C ■> per cent conductivity, R» » resistance of zoo per cent conductivity wire at
*o' C (from Ubic), Rt - resistance of wire of conductivity C at any temperatoije C C.
then

A -Jf-iy + 0.00393 (/-;ro)j

TABLES AND DATA.

469

COPPER CABLES CONCENTRIC LAY.
B. & S. GAGEr-100% CONDUCTIVITY.

Circular

mils

and
A.W.G.

Resistance at
25" C. or 77* F.*

Weight in
pounds, bare

Standard strands

Flexible strands

Ohms

perxooo

feet

Ohms

per

mile

per

xooo

feet

per
mile

Num-
ber of

wires

Diam-
eter of
wires

Out-
side
diam-
eter,
in mils

Num-
ber of
wires

Diam-
eter of
wires,
in mils

Out-
side

diam-
eter,

in mils

2,000,000

O.OOSJ9

0.0285

«i8o

32O00

127

125 5

1631

169

103.8

1632

1.900.000

0.00568

0.0300

5870

[31000

127

122.3

ISOO

169

106,0

1590

1,800.000

O.0OS99

0.0316

5566

29300

127

119. z

1548

169

103.2

1548

-1.700,000

0.00634

0.033S

5250

27700

•127

"5 7

1504

169

100.3

1504

1.600.000

0.00674

0.0356

4940

26100

127

112. 2

1459

169

97.3

1460

1. 500.000

0.00719

0.0380

4630

24500

128.4

1412

127

108.7

1413

1.400,000

0.00770

0.0407

4320

22800

124.0

1364

127

105.0

136s

I,JOO,000

0.008J0

0.0438

4010

21200

9«

119 5

131S

127

101.2

1315

1.200^000

0.00699

0.0475

3710

19600

114-8

X263

127

97.2

1264

I.ICC.OOO

0.00981

0.0518

3400

1790C

109.9

1209

127

93-1

1210

1. 000.000

0.0108

0.0570

3090

16300

128.0

1152

.104.8

"53

9SOfioo

0.0x14

0.0600

2930

15490

124.8

1123

102.2

1124

900.000

0.0120

0.0633

2780

14670

121. 5

1093

994

1094

850.000

0.0127

0.0670

26^

13860

118. 0

X062

96.6

1063

800,000

0.0135

0.0712

3470

13040

114. 5

1031

93.8

1031

750,000

0.0144

0.0759

2320

12230

no. 9

998

90u8

999

700,000

0.0154

0.0814

2160

I1410

107. X

964

87.7

965

630/ioo

0.0166

0.^876

2QI0

10600

103.2

929

84.S

93c

630,UUU

0.0180

0.0949

1850

9780

99.2

893

81.2

893

550.000

o.oi(j6

0.1036

1700

■8970

95. 0

855

77.7

85s

500,000

0.0216

O.I 139

1546

8150

116.2

•

814

.90.5

815

4$o,ooo

0.0240

0.1266

1390

7340

37.

IIO.3

772

85.9

773

400,000

0.027O

0.1424

1240

6520

104.0

728

81.0

729

150,000

0.0308

0.1627

1080

S7I0

97 3

681,

75.7

682

JOOjOOO

0,6.160

0.1899

926

4890

90.0

630

70.x

631

250.000

0.0431

0.228

772

4080.

82.2

575

64.0

576

0000

0.0509

0.269

653

3450

105.5

528

.37

75.6

533

000

0.0642

0.339

Si8

273s

94.0

470 ■

67.3

471

0.081X

0.428

2170

83.7

418

60.0

420

0.i02

0.540

326

1720

745

373

S3; 4

374

0.129

0.681

2SS

1364

66.4

332

47.6

333

0.162

0.858

205

1082

97.4

292.

•19

59.1

296

0.205

1.082

163

858

86.7

260

• 19

52.6

263

0.259

1.36s

129

680

77.2

232

469

134 •

0:326

1. 721

102

540

68.8

206

41.7

209

0:410

2.170

81.0

428

61.2

184

37.2

Z86

0.519

4.74

64.3

339

54 .5

164

33.1

166

0.654

3 45

51.0

269

48.6

146

295

147

*Let C •■ per cent conductivity, Rtt ■* resistance of 100 per cent conductivity cable at
.25* C* ^r^qi \9\M)r Kf ~ resistance of cable of conductivity C at any temperature t C.«

***** " - ^« ["-^ + 0.0038s tf- 25)].

470

ALTERNATING CURRENT SIGNALING.

SOLID COPPER WIRE SOFT DRAWN
BRITISH STANDARD WIRE GAGEn-100% CONDUCTIVITY

0«f«
Ro.

Dkmeter
in mils

Crots-sectioii

Ohms per
leoofeeC,

15-6* C. or
60* F.*

Ponads per
xooo feet

CircttUr

Square
iflches ,

7-0

500
4«4
433

3SO.00O

318.30O,
186.600

0.1964
0.1691
0.1466

0.04077
«.04734
0.05461

756.8
65X.7
564.9

4-0
3-0

»-0

400
373
34S

160.000
138.400

131,100

0.1257
0.1087
0.09513

0.06370
0.07365
0,064x6

484.3
4x8.9
3G6.6

334

300

376

XO5.OOO
90,000
76.180

0.06345
0.07069

0.05983

0.(9709
O.U33

0.1338

3x7.8
373.4
330.6

3
4
5

353

333
3Z3

63*500

53320

44.940

0.04988
0.04337
0.03530

o.x6q5
0.1894
.0.3366

X93.3
X63.9
X36.0

7
S

t93.

176
i6o

36.860

30.980

«.6oo

0.02895
ip.03433

0.0301)

o.af765
0.3290
0.3981

ixx.6
93.76
77.49

10
IX

144

128

116

30.740

I6J80

.13.460

0.01629
0.01287

0.0IQS7

0.4915
0.6331

0.7574

63.77
49-59
40.7^

19 <

104
8o

10.830

8.464
6400

0.006495
0.006648
0.005037

0.9423

•x.aQ4

1.593

33.74
35.63

1937

64
56

5.IS4
4.096

3.136

0.004073
0.003317
O.P034Q3

1.966
3.488
3.350

15.69
13.40

9.493

19
90

40
36

3J04

l.6co

O.OOI8IO
0,00X257
0.001018

4.424
6.37Q
7.864

6.974
4.843
3923

32
34
36

38
33

7«4.o
484.0
324.0

0.0006158
0.0003801
0.0003545

X3.00
31. 06
31.46

3.373
1.465
0.9807

38
30
32

14:8
13.4
10.8

319.0
IS3.8
X16.6

0.0001720
0.0001208
O.OOC09I6I

46.54
66.28

87.3B

0.6630
0.46S4
0.3531

3«

9.3
7.6
6.0

84.64
57.76
J6.00

0.00006648
0.00004536

X20.4
X76.5

^.x

0.3563
0.1748
0.1090

40
43
44

4.S

4.0
33

33.04
16.00
10. 34

0.00001810
0.00001357

443.4
637.0

995 3

0.06974-
0.04843 ,
0.03100

0.003037

0.000000043

1.0

1. 000

10.190

•Let C- per cent conductivity, Rm - resisUncc of xoo per cent conductivity wire tt
60* F. (from tsble), Rt - rcsi»taace o( wire ol conductivity C at any temperat^le f* F^

* •'^•[^t 0.00323 (I -60)]

TABLES AND DATA.

471

SOLID ALUMINUM WIRE
* S. GAGE— <1% CONDUCTIVITY

For Stranded Cablee See Page 336.

•

. o

oooo
ooo

Diam-
eter in

Cross-tectioa

Reeistance at
30« C. or 68* ?.•

Wtifht la pooads

Feet

poaad

Circular
mill

square
iachet

Ohmi

per.xooo

feet

Ohmi
mUe

1000 feet

adto

460.0
409.6
3^4.8

311,600
167,800
133.100.

0.1663
0.1318
0.1045

0.Q604

0.101
0.138

0.424
0.535
o.«75

19$
154

133

1027
81S

S.t4
•.17

324-9
289.3
2$7.6

105^600
83,690
66^70

0.08389

0.0657?
0.05313

0.161

0.303

. 0.356

o.lsi

1.073
1.353

97.Q

76.9

61.0

40$

ko.-3i

1300
16.39

4
5

229.4

304.3
181. 9

52.630
41.740
33.100

0.04134
0.03278
0.02600

tf.323

0.406
0.514

X.^06

3.15

a.71

48.4

38.4

30.4

255

303
160.' 7

26.1

32.9

" 7
8

l63.0

144.3

13B.S

26.350

30,830

16.510^

0.03Q63
0.01635
0.01397

0.648
0.817

1.03

3.42
4.31
5.44

«4.l
19. i

. i5.a

127.4

let.o
80.3

41.4

sa.3

6S.9

* 10
13
14

161.9
80.81

64.08

10J80
6,530

4,107

0.008155
0.005129

0.003235

1,64

3.61
4.14

8.65
13.76
31.9

9.55
6.0Q

3.7&

S0.4
31.7
1993

X04.8

966.6

15
l6

57.07

50.83
45.a6

3.257'

2.583

2.048

0.002558
0.0030^9

0.001609

5,22

6.59
8,31

27.6

34.8

1 43.8

^9$

a.37

1.88

.IS.81

U.54

9.94

334
421
S3X

40.30
3589
31.96

1.634
1,388
1.033

0.001276

0.001013
0.0008023

10.5
13.2
16.7

55.3
69.7
87.9

1.49
K.1&

9.939

♦ 89
6.35
4.96

670

844

X.065

31
33
23

38.46
35.35
33.57

810.1
.642.4
509.5

0.0006363
0.0005046
0.0004002

31.6

26.5
33.4

110.9
139.8
176.3

0.^45.

0.591

0.468

3.93
3.12

tJ43
tj693
t.130

34
35

30.10

17.90

15-94

404.0

.320.4

2S4.I

0.0003173

0.0003517
0.0001996

42.1
53.x
67.0

333
380
353

0,371
0,395
0,334

X.961
X.556
^.233

a,69o

3.390
4.280

27
29

14.20
■ 13.64

11.36

301.5
159.8
126.7

0.0001583
0.0001355
0.00009953

84:4
X06

134
i69

313

269

446

563
709

•894

1137
1421

0.185
"0.147
0.XI7

0.978
0.776
0.615
0.488
0.387
0.307

5400
6310
8,580

•

to.830
13.650

17,310

30
31
32

10.03

8.928
7.950

100.5
79.70
63.21

0.00007894
0.00006260

0.00004964

0.0934

0.0733

o,058t

33
34
35

7.p?o
6.305
5.^5

.50.13
39.75

0.00003937
0.00003123
O.OQOO3476

.339
438

540

1792
3260

2850

0.0461
0.0365
0.0390

. 0.343
0.1929
O.IS30

21.700
27400
34410

36
38

. S.opo
3.96s
3 145

25.00

15.72
9.888

0.00001964
0.00001235

681
1080
1720

3590

5710
9080

;O.0a3O

0.0145
0.0091

0.12X4
0.0763
0.0480

4)iSP0

69,300
110.060

O.OOOOO77OD

*Let C » per cent oonductivity, R» • resistance of 6t per cent ooaductivity wire at
20* C. (Crom table), Rt^ resistance of wire of conductivity C at nay tempoatvie tCn

"*^ JI,* 5^(1+0.004 tt-toJl.

472

ALTERNATING CURRENT SIGNALINa

BARE GALVANIZED IRON AND STEEL WIRE
B. W. G.— EXTRA BEST BEST— BEST BEST— STEEL

Wcighia.
Pound*:

BrMJiing
. Pouada.

9 w^^^^wl^P^^W*^^^^» M 9m

OhttM per mile.

LOOO

FMt.

fia

Iran.

8M.

E. 0. B.

B.B.

steel

340

304.

1607

4821

9079

2.93

3.42

4.05

300

237.

1251

3753

7068

8.76

4.4

5,2

284

212,

1121

3363

6335

4.19

4.^1

5.8

269

177.

932

2796

5268

5.04

5.9

!».97

238

149.

787

2361

4449

5.97

■

6.99

8.20

220

127.

673

2019

3801

6.99

8.18

f :o6

203

109.

573

1719

3237

8.21

9.6

11.35

180

85,

450

1350

■

2545

10.44

12.21

14.43

165

72.

378

J 134

2138

12.42

14.53

17.18

148

58.

305

915

1720

15.44

18.06

21.39

134

47.

250

750

1410

18.83

22.04

26.04

120

38.

.200

600

1131

23.48

27,48

32.47

109

31.

165

495

933

28.46

33.3

30.36

•

24.

125

375

709

37.47

43.85

51.83

18.

288

541

49.08

67.44

67.88

13.7

216

407

65.23

76.33

90.21

11.1

177

339

80.03

93.66

IIO.T

8.9

141

264

100.5

.120.4

139.

6.3

189 '

140.8

164.8

194.8^

TABLES AND DATA.

433

COPPER CLAD STEEL WIRE
Standard Underirround Cable Co.

Tliie wire conmts of a steel core to which is pennanentl^ welded a concen-
tric coat of cc^pcr. It is inade in several grades ditfenngi.in the relative
thpekwipse of the copper coating, the grades being designated by the oorree*
ponding con<9uctivi^ expressed an per cents of Matthiesseii's Mandard: for
eittLmple 40 J( cc^per clad has a conductivity of 40 J( of that of a solid cop-
per wire of the same gauge.

Due to the use of the steel core, an appreciable "skin effect'* is encoun-
tered when copper-clad wire is used f or transmittii^ alternating currents
and the reader is referred to page 517 for impedance date at the commercial
the table below gives the ohmic resistance only.

Croca-Mction

Resistance at
33^** Costs'*^

Weight in

DiAm-
eCer in

0U|S

Feet
P«t

pound

Gage
No.

Ciroilar

Squere

Ohms
per

Ohms

mils

inches

1000
feet

peTj
mile

1000
feet .

mile

0000

460.0

311,600

0.1663

0.133

0.649

59S

3x40

X.66

coo

409.6

i67*»

p. 1318

0.154

0.813

471

2490

3. 13

00«

364.8

133.100

♦.1045

0.195

1.03

374

1970

a.67

324.9

105.500

0.06389

0.346

X.30

297

1570

* 3.37

289.3

83.690

0.06573

0.310

l.<l«

335

X240

4.26

257.6

66.370

0.05313

0.390

186

9te

S.38

239-4

52,630

0.04134

0.492

3.60

148

781

6.76

ao4.3

41,740

0.03378

0.633

3.28

1x7

6x8

B.5S

181 .9

33,100

0.03600

0.783

4.13

93.9

•491

X0.76

x62.o<

36.350

0.03063

0.987

5.31

73.7

389

1357

144.3

S0320

0.01635

1.35

6.60

58.5

309

17.09

X28.5

16,510

0.01397

1.57

8.29

46.4

245

8X.6

114. 4-

13.090

O.OI038

1.98

10.5

36.8

194

27.2

X01.9

IOJ80 .

0.008155

3.50

X3.2

39.3

X54

34.2.

90.74

8.334

0.006467

3.15

16.6

23.x

X33

43.3

80.81

6,530

O.P05I29

3 97

*3I.O

18.3

96.6

54.6

71.96

5.178

0.004067

5.00

36.4

X4.6

77.1

68.5
87.0

64.08

4.107

0.003235

^.31

33.3

XI. 5 60.7

• Ut c
then

per cent conductivity,

resistance of 40 per cent conductivity wire at 23.9* C. (frooi table),

resistance of wire of conductivity C "St temperature <* C,

£t

^2^ li + 0.00433 «- 33.9)1.

474

ALTERNATING CURRENT SIGNALING.

TENSILE STRENGTH OF COPPER Wlflfi

Siseorwira.

*
BrMUucWMchtoC

i-a- -y^^

^ Br«iJcii>cW«i;ht of

0000

9971

565a ,

. 000

7907

4480-

♦ » *

=■■.;■...■ 00-^

£271

3653

..:. 1 ..

: ... V' 0

4973

2818

3943

2234

. ■'. '.

•■ 2 '

3127

1772

•

2480

1405

■

1967

U14

1559

883

1237

700

980

555

778

440

617

349

489

277

388

219

307

174

244

138

193

109

153

. il6

J33

(55

Copper Wire.
98% PURE. SPEC. GRAVITY 8.89.

or,

d»

.or.

• 330.353
d»

30.811

or.

or»

62.667

10180.694

d»

10507.4

Weight per 1000 feet- «003027Xd*
Weight per mile- .015983Xd>

Resistance per 1000 feet ® W> ^^--y^,^, ^ooOfeet
Resistance per 1000 feet @ 75* F.-^^^L^^^...-^^^

Specific conductivity of Pure Copper is 100 (100 inches pure copper weighing 100
grains @ 60° F.— 0.1516 ohms), of oommeroial copper from 96 to 102 per cent, of
standard.

The percentage of conductivity of copper is found by measuring the resistance of a

■ample of the same length and weight as. the standard and at the same temperature.

lOOxR
R— resistance of standard, r— the risistanoe of sample. —per cent, con*

ductivity.,

TABLES AND DATA.

475

CARRYING CAPACITY OF INSULATED COPPER WIRES

The qneslion .of dfop iis not t&keft fiAo oofisidemtton in these tables.

Concealed

Exposed

1 Il.ubber-Cov«r«l

WeatbM-prool

Copper B. A S. Cause.

Wires.

Wires,

Amperes.

32'

110,

131

ao7

156

127

185

00'

150

220

000

177

262

0000

210

312

arciilar Mils.

200,000

■:> . 200

300

' 300,000
400,000

270

400

330

500

500,000

390

590

600,000

450

680

700,000

500

.760

, '

(800,000

550

840

* - ^

900,000

600

920

". . '^•

i, 000,000

650

1,000

1^100,000

^90

1,080

• '-;

1,200,000

730

1,150

■

1,300,000

770

1,220

1,400,000

«10

1,290

1,500,000

850

1,360

i,6po;ooo

SdO

1,430

1,700,000

•930

! 1,490

1,800,000

970

1,550

1,900,000

' 1,610

1,610

2,000,000

1,050

lf670

The above table shows the allowable canying^ capacity of wires and cables of 98
per cent» (conductivity.

The lower limit is specified for rubber-covered wires to prevent gradual deterioration
of the iimtlation by the heat of the wires, but not from fear oj igniting the insulation.

"N, B.O/F. U"

476

ALTERNATING CURRENT SIGNALINC;.

COPPER MAGNET WIRE— SINGLE COTTON COVERED

Bare
B. &S.

Wire
Dia..

Max.

diam.

ins. wire

Turns

per

sq. inch

Ohms per
Cu. inch
26*»C.

Pounds

per cu.

inch.

10
11
12

.102
.091
.081

.108
.097
.087

85!56
106.29
132.02

.00726
.01134
.0177

.2260
.2223
.2189

13
14
16

.072
.064
.057

.078
.070
.063

164.36
203.91
251.86

.0280

.04395

.06845

.2150
.2106
.2068

16
17
18

.051
.045
.040

.057
.051
.046

307.05
384.16
472.19

.1044
.1675
.2606

.2096
.2046
.1996

19
20
21

.036
.032
.0285

.041

.0376

.034

695.36
710.75
864.94

.4291
.6130
.9399

.2032
.1994
.1941

22
23
24

.0265
.0226
.0200

.031
.028
.025

1037.0
1274 . 0
1600.0

1.408
2.126
3.531

.1887
.1829
.1761

25
26
27

.0180
.0160
.0140

.023
.021
.0196

1889.0
2266.0
2629.0

5.146

7.814
11.84

.1690
.1617
.1628

28
29
30

.0126
.0110
.0100

.018
.016
.015

3086.0
3906.0
4443.0

17.16
28.61
39.24

.1465
.1369
.1288

31
32

.0090
.0080

.014
.013

6100 .,0
6932 .0

55.69
81.86

.1208
.1128

TABLES AND DATA.

477

COPPER MAGNET WIREr— DOUBLE COTTON COVERED

Bare

Wire

B. &S.

Gage

Dlam.
Bare
Wire

Max.

diam.

Ins. wire

Turns

per
sq. inch

Ohms per

cu. inch

® 25*» C.

Pounds

per cu.

inch.

0
1
2

.325
.289
.258

.346
.310
.278

8.352
10.400
12.93

.0000698
.0001098
.0001714

.2308
. 22972
.2276

4
5

.229
.204
.182

.250

.224
.202

16.00

19.926

24.50

.0002692
.0004226
.0006525

.2262

'.2251

.2215

6
7

.162
.144
.129

.180
.162
.144

30.855

38.08
48.23

.001037
.001619
.002559

.2188
.2150
.2112

9
10
11

.114
.102
.091

.127
.113
.102

61.98
78.32
96.09

.004206
.006644
.010248

.2068
.2093
.2047

12
13
14

.081
.072
.064

.092
.083
.075

118.156

145.15

177.76

.015901
.024711
.038313

.2003
.1946
.1887

15
16
17

.057
.051
.045

.0675

.061

.055

219.48
268 . 63
330.51

.059643
.091176
.14411

.1826
.1886
.1826

18
19
20

.040
.036
.032

.050
.045
.041

400.00
493 . 73
594.87

.2i2P71
.35586
.51304

.1754
.1673
.1614

21
22
23

.0285
.0255
.0226

.037
.034
.031

730.00

864 . 89

1040.06

.79283
1 . 1747
1.7345

.1539
.1462
.1387

24
25
26

.0200

.018

.016

.029
.027
.025

1188.87
1371.96
1600.0

2 . 6246
3.7376
5.5172

.1286
.1210
.1123

27
28
29

.014

.0126

.011

.023
.021
.020

1889 . 8
2267.6
2500.0

8.5198
12.6071
18.2408

.1023

.09442

.08470

30
31
32

.010
.009
.008

.019
.018
.017

2769.9
3086.2
3459.8

24.4648
33.6417
47.7424

.07793
.07063
.06347

476

ALTERNATING CURRENT SIGNALING.

COPPER MAGNET WIRE— SINGLE SILK COVERED

Bare

Wire

B. & S.

Oage

Diam.
Bare
Wire

Max.

diam.

ins. wire

Turns

per
sq. inch

Ohms per
cu. inch
@ 20 *•€.

Pounds

per cu.

inch.

24
25
26

.02010
.01790
.01594

.2023
.0201
.0181

2010
2475
3055

4.29

6.66

10.37

.2027
.2023
.1976

27
8 ,
G

.01420
.01264
.01126

.0163
.0148
.0134

3765
4565
5580

16.1
24.7
38.0

.1865
.1830
.1707

30
31
32

.01003
.00893
.00795

.0121

.Olio

.0100

6830

8265

10000

58.6

89.5

136.5

.1724
.1688
.1624

33
34
35

.00708
.00631
.00562

.0091
.0083
.0076

12075
14515
17245

207.8

315

473

.1499
.1462
.1369

.00500

.0070

20400

704

.1292

COPPER MAGNET WIRE— DOUBLE SILK COVERED

Bare
Wire
B&S
Gage

Diam.
Bare
Wire

Total
Thickness

of Ins.
(nominal)

Max. Ins
dia.
wire

Turns

per
sq. in.

Ohms

per cu.

inch

20" C.

Pounds

per cu.

inch

24
25
26

.02010
.01790
.01594

.004
.004
.004

.0243
.0221
.0201

1695
2050
2475

3.62
5.52
8.40

.1708
.1677
.1600

27
28
29

.01420
.01264
.01126

.004
.004
.004

.0184
.0168
.0154

2955
3545
4215

12.7
19.1
28.7

.1462
.1421
.1288

30
31
32

.01003
. 008928
.00795

.004
.004
.0035

.0142
.0131
.0116

4960
5825
7420

42.6

63.1

101.3

.1252
.1189
.1205

33
34
35

.00708
. 006305
.005615

.0035
.0035
.0035

.0107
.0100
.0093

8735
10000
11565

150.4

217

317

.1084

.0990 :

.0915

.00500

.0035

.0087

13210

456

.0837 ;

TABLES AND DATA.

479

RESISTANCE OF GERMAN SILVER WIRE

B. & S. GAUGEr-70» F

18%

ALLOT.

30%

ALLOY.

ReBii(tanee>Taries .08 et oae |kf r

ResisUnce variei .023 of «iie ^r

cent, for one

«ent. for one

dcgre« Centignd*.

Ohms per

Ohms

Ohlns per

Ohms

SIZE.

1000 feet.

per pound.

1000 feet.

per pound.

No. 8 1

11.772

.24702

17.658

37054

'' 9

14.83

.39249

22.22

.58873

*^ 10

18.72

62443

28.08

.93666

44 11

23.598

.99281

35.397

1.4927

»* 12

29.754

1.5785

44.631

2.3676

" 13

37.512

2.5101

56.268

3.7660

44 14

47.304

3.9911

70.956

5.9862

'' 15

59.652

6.3462

89.478

9.5192

" 16

75.222

10.090

112.833

16.135

^ *' 17

94.842

16.045

142.263

24.066

** 18

119.61

25.511

179.41

38,266

*^ 19

155.106

42.909

232.659

64.3^

** 20

190.188

64.498

285.282

96.5^

*c 21

239.814

102.56

359.721

153.84

*v 22

302.382

163.06

453.573

244.60

" 23

381.33

259.33

571. 99

388.99

u 24

480.834

412.37

721.251

618.55

'' 25

606.312

665.61

909.468

983.43

** 26

764.586

1042.7

1146.879

1563.8

" 27

964.134

1657.7

1446.201

2486.6

*' 28

1215.756

2636.0

1823.634

3953.9

" 29

1533.06

4191.5

2299.59

. 6287.2

•* 30

1933.038

6666.5

2899.557

9999.6

" 31

2437.236

10594.

3655.854

15890.

** 32

3073.77

16850.

4610.65

26275.

•' 33

3875.616

26788.

5813.424

40181.

'^ 34

4888.494

42618.

7332.741

63927.

" 35

6163.974

67759.

9245.961

101640.

** 36

7770.816

107700.

11656.224

161540.

** 37

9797.166

171170.

14695.749

256770.

" 38

12357.198

269820.

18535.797

404740.

" 39

15570.828

428720.

23356.242

643070.

** 40

19653.57

682540. r.

29480.35

1023800.

480

ALTERNATING CURRENT SIGNAUNG.

TWIST DRILL AND DRILL ROD GAGE
(Brown dc Sharp Mf y. Co.)

»-'

No.

Sice in
Deci.

mals.

No.
15

Size in

Deci.

mals.

No.
29

Size in

Deci.

mals.

No.
42

Size

Deci.

mals.

No.
55

Size
•in

Deci-
mals.

No.
68

Size in
Deci-
mals.

.2280

.1800

.1360

.0935

.0520

.0310

.2210

.1770

.1285

.0890

.0465

.02925

.2130

.1730

.1200

.0860

.0430

.0280

.2090

.1695

.1160

.0820

.0420

.0260

.2055

.1660

.1130

.0810

.0410

.0250

.2040

.1610

.1110

.0785

.0400

.0240

.2010

.1590

.1100

.0760

.0390

.0225

.1990

.1570

.1065

.0730

.0380

.0210

.1960

.1540

.1040

.0700

.0370

.0200

.1935

.1520

.1015

.0670

.0360

.0180

.1910

.1495

.0995

.0635

.0350

.0160

.1890

.1470

.0980

.0595

.0330

.0145

.1850

.1440

.0960

.0550

.0320

.0135

.1820

.1405

MISCELLANEOUS FORMULAE FOR COPPER WIRES

Diameter in 0.00 1

Circular Mils X

0.000003027 X

0.003027 X

0.015983 X

0.003854 X

330.353 -^

0.0%585 X

10.353568 -5-

inches Squared
0.7854
Circular Mils
Circular Mils
Circular Mils
Square Mils
Circular Mils
Circular Mils
Circular Mils
Brefiking weight of Wire -i- Area

sq. men.
Breaking weight per sq. in. X Area = Breaking weight of

wire.
Weight of copper = H times weight of iron wire of
same diaineter.

Circular Mils.
Square Mils.
Pounds per foot.
Pounds per 1000 ft.
Pounds per mile
Pounds per 1000 ft.
Feet per pound
Feet per ohm.
Ohms per foot
Breaking weight per
sq. inch.

TABLES AND DATA.

481

STANDARD WROUGHT IRON PIPE
BLACK OR GALVANIZED

Diameters

Weight

per foot

^Cotiplings

Size

(-1

g 1

3 1

•s 1

H 8

.40s

.269

.068

.244

.245

27 '

.562

.029

.540

.364

.088

.424

.425

.685

X .

.043

.675

.493

.091

.567

.568

848

iVfe

.070

.840

.622

.109

.850

.852

1.024

.xx6

x.oso

.824

.113

I.X30

1. 134

X.281

.209

1.31S

1.049

.133

1.678

X.684

11%

X.576

.343

H/4

X.660

X.380

.140

2.272

2.281

ii¥i

1.950

.535

iy3

1.900

1. 610

.I4S

2.717

2-731

11%

2.218

.743

2.375

2.067

.154

3.652

3.678

IIV2

2.760

2^^

1.208

2V2

2.87s

2.469

.203

5. 793

5.819

3.376

X.720

3 Soo

3.068

.216

7-575

7.616

3 948

2.498

4000

3S48

.226

9.109

9.202

4.59X

4.241

4. Soo

4.026

.237

•

10.790

10.889

'5. 091

4.741

4V3

5000

4.S06

.247

12.538

12.642

5.591

5. 241

S.S63

S.047

.258

14. 617

14.810

6.296

8.091

6.62s

6.065

.280

18.974

19.185

7 358

9-554

7.62s

7.023

.301

23.544

23 769

8.358

10.932

8.62s

8.071

.277

24,696

2S.OOO

9.358

13 90s

8.62s

7.981

.322

28.554

28.809

9.358

13.905

9.62s

8.941

.342

33.907

34.188

10.358

17.236

xo.^50

10.X92

.279

31.201

32.000

II. 721

29.877

X0.750

10.136

• 307

34.240

35 000

II. 721

29.877

I0.7S0

10.020

.365

40.483

41.132

II. 721

6V8

29.877

XI.7SO

11. 000

375

45.557

46.247

12.721

32.550

X2.7SO

12,090

.330

43.773

45.000

13.958

43.098

I2.7SO

12.000

.375

49 562

50.706

13.958

43098

X4.000

I3.2SO

.375

54.568

55.824

15.208

47.152

X5.000

I4.2SO

.375

58.573

60.37s

16.446

6^i

59.493

16.000

IS.2S0

.375

62.579

64. sop

X7.446

6Vb

63.294

The permissible variation in weight is 5 per cent above and 5 per cent l)elow,'

Furnished with threads *and couplings and in random lengths unless, otherwise
ordered.

Taper of threads is % inch diameter per foot length for all sizes.

The weight per foot of pipe with threads and couplings is based on a length 0I
30 feet, including the coupling, but shipping lengths of small sizes will usually
average less than 20 feet.

All weights given in pounds. All dimensions given in inches^

482

ALTERNATING CURRENT SIGNALING.

TRIGONMETRIC SINES AND COSINES

a 00 1* «D to ^ CO C9 Vh QCdoorocok0^eoc9^od>oor«
•D«OoOoOoooooooooooOt*t*^-^-^*t*t*t*•^•^-co;ocD

•

•^*cor-*-<iOOOi-i'^coooooao&oo<oeoo»oococoi-^

*-'<*C^Oir<-"*rTH05C0090t-'««**«-iOOiOWCS»OC^30'«*0

t-iC0»0«00OC^e0»0t-.0:OW'*»0r*c:OC^'^»0t^0>
00000»-i»-i»-t^'-«rHC^M««lMC^cococoeoec»

OOOOOOOOOOOOClOOOpOOOQOO

•^oseo»c?0"«*oooi«oooot-wo*-«'<*o&»ocao&iOi-^»o

^0)^0DC4CD0»S^»0r~OO-<rHQ00tOC>l00esiO0dO

''1'.— Oi«0^»-ioocoeoOr'»oc«aOi«d5^»o»coc^Ci»o*-«oo

<-iCO-^<OOOOi~ieO«Ot«>ODOC«CCi4^^000C4000r-00

ooooOt-i — '-•i-ii-iT^wc^ci?5c^cMcc«ooooeoeo

»*

oodoooo.oooooooooooooooo

^aaC0x0«0'^0ii-l0&C!IOC«00b-O'«*'O00C0»0«-Ht^

«O»00iC0i^O^?00S^CilCVI(N(MO00'n>Ou»0iC4C0

2i.

rH0»«0'?0i->C0?0CCOt^»0CN«0iC0«0O?0C0O«DC^CSi0

»-lC^'^CCXOi»-ieO»OCOOOO«-HCCkOl--000'M«OCOOO

000000-^-'»-i^»-iOC<IC^CMCMC«CCCO«COCCCO

o o d d o o do ddddddddddddddd

t^rH<DO'^OOC^^^OOOO(NCOT»^'«^ 55. (N O r- CO 00 CJ O «©

00<0ei0^00v0C0Or-O(NC»5C)CCOt-'^Ot-C0OCDei

000000«-H — i-Hi-ii-iT-ic^cacjCMCMcoeocccococo

dddddddddodoodddddd d.d d d

Cat^i-^OCDxOi-i'^eOOOOONOCMO'WCOCOiOOOOOSO

00 CJ r- »-i »c o>«oooi'^coto<o«o»0'<ij<c^c; oo-^r-si

kOCCOOO»OC»Of^"^C^Ci®COOi'^"^»-«r>-'«j< — t-cocs

Oc^'^ot-cSf-iCMTt'Or-Oi'-ico-^ccoooi-Heo'^cOi-'

OOOOOO^r-^T-lT-iT-irHCMCMC^CMOlCSJCOOOOOOiW

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ooooooooooooooooooooooo

•-HcOf-^-^ffcotocacoiOf-ii-tcocoooT^eoeokOcoc^xoooo

0SC000C^«0Q'^r>-O«»0Ot^X^t^C0<^i-Ht>.C0t^OC0

C10r'iO(MOt^'^<N06«OCCOi^'<J<-'OOxO»-'OCTj< •-!•»-

OdCO»or-CiOC^"^iOt^c»'^(M'«r<:ot*-os>-HC^'«f cor-

T-H

OOOOOO'-i'-''-^'-''-'— «CMCJC^<NC^CJCOCC«CCCO

»o

OTi»occ»r'»-iicco»-<->«t<cDooo5a><r-oococco»ooeoco

o^-"^c^^O^^'^-^occccoJ^- 'si'-^ccoc^ooc^oOti*

O■^-^CC»0O0C?O(MC0l0^-OOCN•rJ^^0^^05OC^'^^0l^

000000'-''-<'-<»-«'— ''-•I^^NCVICIC^CMCCCOCOCOCO

dddddddddddddddddddddpd .

O r^.w C0'^>o«t*«ci0^c^je0'«*»occ>r-oooso*-«c«

r-l«-4f-it-it-i«-4r-«r<ir-«i-4C9e>«e«

TABLES AND DATA.

483

TRIGONMETRIC SINES AND COSINES

OC^rSiOCOOOO'-^CVI'^tOt^OOO-^C^'^kOOaOAO

dodcJddocJoodoodocJddo'doo'.

o.ooooooooooooooooooooo

•*'».i-icocor-o>OOs^-coooo^Or»««ooot*'*ot
OOOOOOOOOOOOOOOOOOOOOO

oooooooooooooooooooooo

go»oooosr-ooj«e^'*j<i-«i-i«oo»0'*coeo^'«i<'*c5
OOoovOi-4coooooooooeO'<r'^c^ooc>»i"^oig5

o:i-«c«'«*iot«-oooc»cOTr«oi>oo<NcO'**<cc*^coo

oooooooooooooooooooooo

<-Hea)O0000<^kOC4eC0000QCO^'^tO00«-l»OAC9iO

■^ooC40i00eokOkOeoocoa)— •i-iOkOOoi'M'-ir*

eOOiiOOCOC^t^'Mt^C^H— »-iiOO'*t— '-»0«0^'««»'«0
O5Off«'^»Ot«-00O'-«C0'^C0t^0tO'-«C0'*»Ot<-C00a

OOOOOOOOOOOOOOOOOOOOOO

eO"»*oJt^oat^i-i0^c«'*05ooo50»«cioaowo«»

t»t^OCOCiTrOOOOCiO«-^»OI->'QO;OCOr>-0-^0«0
O«0C«00C0O'^O»0C5"^CiC0r-i-iiO0i<N«00JC^^T
OOC^eOU3COOOO'-<CMrfuOt^O&Or-iCI'i9-»0?0000>

oooooooooooooooooooooo

•

€0'*iOOt*0000'-iC^eO'«r»0<Dt-000>0»-iWO*"^

c^c«CMff^c«CiJC»cocoeocoeococoeoco«'<"i»'i»'<i'^

«4

ALTERNATING CURRENT SIGNALING.

TRIGONMETRIC SINES AND COSINES

'^'V^'weoeoooeoooooeoeoooeQC!ic«C9e9C«c«C49«

w
Q

e^eoi-ir^O«-<OcoO — OC0O'-«Occ>CJOt-e0i0»0»-*

0-^CO"VCOt^000005»05QOOOt-«DTrCSI-<OOCOCOOr^

^c3'««*udor«oooiO<->c^eo'viOcoroGOCdadQ<-*cac4

t^l>t-r^i«-t*Jt't>-0O000000000O0000000O00^O»OiO»

c«r-o©*--<oaooooo*^ooo*-t**^QOooc«ooco«ooi
coeoc^oO'^eoc^ooco'*'^o»orD»ooao«»ooeocoo

-^C'l-vocot^ooo&O'-'e^W'^ocDi'-ooaooiO — '-•c«

ddddddddddddddddddddddd

o&r«'^GOOdt^C4e^aoor*Od»ocooooO)Oeidmcoc90»
Oi^0ioc^co'^»o»o»0i0»0"^'^eo^0aocoeo^-Q0'^

r-iMCC»OC0t*000iO'-'CMC0"^»OCDt*00000iO'-»'-<0«
I-'t-l^r^t-r-t-t-OOOOOOOOQOOOOOOOOOOOOOOSO&OiO*

OOOOOOOOOOOOOOOOOOOOOOO

tor«oocD«H9»«MtacDC9eea»o&^eo«oc9i-ieidO»cocooo
C0k0i^oo0'-ic«wco"<«»<'^eo«c^»-i0oot-"«!rc«»t*ec

t^ t» t— t» t» t^-fc" t^OOOOOOOOOOOOOOOOOOOOOOO&OS^Oi

oooooooo.ooooooooooooooo

*-ijr-»-ieoi-Nr-o:>coc«csiooooeoc«iOC«w««co»oo«

»-iCCOt-000iO^CMCSI0^CMi-i*-4O00t^»0C0»-00OC<l
•HC^C0"rf»0CD00 0iOT-i0»C0-^x0c0C0r-000aOO»-«C«
t^t^t^t-ot^t-ot^t^OOaOQOOOOOOOQOoOQOOOaOOdOdO^O^

oo ooooooooooooooooooooo

«0eOC0O»e4«-^t^Q00CSlC4cOiOO)CDG0eO>^CMr«eoeid«<i}«

^cocoocooiOdaoeot«aococM>o«o^oeoeootOt<-co
05'-«co»ocDr'CCosoooooosoor-?0'^c^ot-'^»-^

t«j^-t^t^t^t«t«t«ooaoQoaoouaooc^aoaoaoaoo)0»o»Od
OOOOOOOOOOOOOOOOOOOOOOO

•

i-ieOeC^t-Oi-iOCOO'-OCOOT-i05CO&Ot^CO»00
r-c:^HcoTrcot^ooooo:ooiooooj^-eO'«Tca—<OOcoeoo
0'^CO'^»OCD^-00050»-incO'^»050l^OOOiOiO»-«0«

t^i>t^t^i-^jt><;t^i>t<-ooooooaoooQqGOoqaooooooa»A
ddddddddddddddddddddddd

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'<«<^'^'^'^kOkOtO«0«OKOkeiOkO»OCOCOCOCOQD«0«0<0

TABLES AND DATA.

485

TRIGONMETRIC SINES AND COSINES

aOO:>C4CDi-H«eoor^kOeOi-io:>r*kOe^OCDC90»»o

DtCO'«t<OUdCO<01>t^l^OOOOaOOC)OiO)000^0

• ##• ##• «»• • »• • •••■• •• ••

OOOOOOOOOOOOOOOOOOOOOf-^

cceoM'kOOco^oor't^QOoboooociCtc^OiOiOiOiOa

O^ Ci C& O 0> Od O^ O) O) Od 0& 0> O O^OOiOO^OOdO^ 0&

oooooooooooooooooooooo

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O^ Ot 0) O^O^OdOOdOdO^OOO) O A O Oi d Od 0^ Od o>

• ••••••••##«•• * • • • • » • •

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O CO C<l 00 CO

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b O Od Oi O^ Od A O^ O) O) O^ Od O O^ Od d Oi O O) Od Od

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s ^^ ^ ^^ <^ ^* r*k <^ r^k*"^ <•»«"*<•»<— ^/—\<'^*'^<*»*'^^•^<»k,

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t* C« 00 CO »fl> »0 CO 00 O M »o CO *^ -^n r* o w

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v«D^*t<•t«t<•^*^*^*^<*^*^*ooaoooaoaoaoaooo

486 ALTERNATING CURRENT SIGNALING.

■•'1 «• «■

TRIGONMETRIC TANGENTS AND COTANGENTS

C00O000000000000fl000t^t^t-l>t^t-t't-t-t^«OcD«O

•

cDCM«-^eid0300^oocooocor^cc>kOiOeoc4e<tr«cDeooo
o d do ddddddddddddodddd'dd

>Oi-i050<0«OCCOOOWCOC«^'^eOO»OwOOOO€0»OxO
»00'<1<OOt-ioO«0 "^CO CO »0 00<MOO«OiOt>-0«D»0«00
^c>J03i^"^c^ost-iOco-'0>r-cO"^cocj-H^O©0«-^
'-•CO'^'COOO'-HCOiOt-OSOC^TrCOOOOCM^CCCOOC^
00000'-H»-if— -^i-i^C^clclc^c^C0CCCO«W'«if"«J'

ddddddoddddddddddoddo o d

■^O0000C0C000-<C0CCiO00»O«OI?0C0©«O©00e0

«-iC5«'^^05«o-*'C<iooo<r>-^coi-HOOtoot-t>-r-t^t-

000000'^.'^r-ii-ii-iCMC^C^C^C^C««eOCOCCeOCO'*

dddddddddddddddd do d d d d d

'(e«o«o«oos"«*«u5iO'*"^»ooooc^w»^ooe«0'-ii-«

00CO«i^00«OCO — Cir-»OCO^OOOt^?OiO"r'*COCO"^
OCM-^COt-O — W'*«OOOOCl'»J«iOt-0-^eO»Ol^05»-»

oooo©Or-""T-i,-Hr-.c«c»o»c«ic^wcocoeoeocoTf
ddddddddddddddddddddddd

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C9aOkO''^aotOOoaoioeoeoiOOC903tooco>et^)0*-)

Q0Clt^C«r-e00JC0"^CC«'*«DOiOi^O«-'«'00U5iC>00
iOC0O00iOC0O00<0'*C<lO00t^»0'*C0CS|»-^O©OO

OC^^iOr-.»i-'CM'^?ooo©T-ico«or'05'-cc>oi^^»-<

1-4

o»eooocooO'^ot-»occco-*«Da>^©ooa)^«eo»c!i"*
ci©t^oc««©oovoco»-*c5t>-»o«)C^^oocooi^t-r^^-

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00©0000©©©©©00©©0 0 000©0

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Ov-^e^eo^tocot^tb o©t-icieo<^»OQOt^Q090<-ic^

TABLES AND DATA.

487

TRIGONMETRIC TANGENTS AND COTANGENTS

c5«"»ot-ecw«oo2:»2Si2 5«^ 5;: ;:;: S ?; jS fS

Ig-g oc o « S P O w ^ t- O <N O 00 o cc « o eo c6

o o' o d d do © oo © o © © ©©©©©©©^

t2E!SS©»o'««*oi»ooc^<Noo — oco<f»:--r;r:io©c2

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S S i§ C^ c3 " S 0> OO.-i © O CO ^ © 2J C^ -J © t- v£^

S§Jocj'^€0©c*j©»-<coi^t-'^'-<©a>©©— "^oo

eo§Soc55Jcbo— «'«**©© — '*t-O<N»<5 00<N»A00
^I5»'*SJbkCvO»CCO©COCOt-t-t^000O00QOO»©©

d d d d d d d d d d © d d © d d © © d © d d

— noooob-©t^»ci©t^©co©eoco^^oococ5t*«©

«^ri-S»r%iOO5t-©00©00'MS^I©e*?vW©*^C0©t—

5SSgS^co«-w«OQO-co©©cvj|5oo-^;5;oo
^iJf;t5j«^OiOicto«ococo©t>-t>-^-t-C30gooo©©©

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•^»OiO*^iC©cococot-^i>;i^t— , oqoqoq©©©*

d d © d © © d d d d d d © © d d d © ©>

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ClCOCOCl«0CviC0eO.90COCOCOCOCOC0CQC0^^'T'^'«l'

488

ALTERNATING CURRENT SIGNALING.

TRIGONMETRIC TANGENTS AND COTANGENTS

^ -^ <^ -^^-^ eoo»«»coode9eoei»eo.eSoic4e4C9C48^C4C9

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03553
07237
11061
.15037
19175
.23490
.27994
32705
.87638
.42815
.48256
.53981
.60034
.66428
.73205
.80405
.88073
.96261
05030
14451
.24604
.35585
.47509

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)0^0'^r^99t-i«-^ao«He^eo^<o«^»oc900»'^e4coc9

iO0£t^Odt^eot^t-i<o<o^'«<«ooioOkO<Pt^coeoeociC9

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O CO « Od 00 CO Od «-^'co «OOOCO(PiOeOCO<Pe^CO<<^Odt^0»
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rHi^-^cocoiOO>"Oeoeo«c«-»^»-<eo»doat-^©r-i-i"^

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a0i0C0'-i-i00CSICDi-iG0O0>t«roCQt«^OQ0i0^t^O

.tO<— ■oot^i^aoc4t^kO'^i>«--*CdOoeocD^coiOQeoio

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,i.H^,^tii4i-<li^«-i«-4r^rHrHi-ii-^rHr-if-4rHr-lf-i09C9C9C4

OkOco«oot«AO»oeoi-ikoaooooioor«cooOkOO^

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S eO J- ^lOOiCOt-Cit^C^OOCOO^COOGOO*©"**^!©

,^r^r^^rHrHf-ii-i«-^«-if-4i-<l^^.f-if-4f-4«-i^rHC9C«C999

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^^^^^kOiO>O»OiOiOiOiOtOtO««OQ0CO«CO««O

TABLES AND DATA.

TRIGONMETRIC TANGENTS AND COTANGENTS

^p0»00l«CD«O^«9e<«-*OC>a0^«Di0^MC«*4O

CH 09 ^4 ^4 ^^ 1^ 1-H r^ r^ 1-4 ^4 tH.

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Q'^6<9CDoo-^Ot^'««o»oc««t<«eoeoeoocOv^C40.
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^ »» 0» 0 C« -^ t^ 0 00 t« 1-4 CD eO ifH 1-4 0 -^ CO 0 «D C4 ,
C4C9C«090O0Oe0'<«>^'«iO»OCD^00O»i-i'<«< 0)001^ T

' r4 1-H 1-4 C4 lO .

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<ocoo^i^*oo<Dr^e<4aoeooc4OeO'«jt«o«0aot^
C4C4t«»^»^o»$*H^aoiOcD^<-ooeooa;)CD«owooeo.

ooc4t^'«*>eO'<>acoi>-eo«Di>-ocOkOOioe^t^eoor-

k0t*00OCM'<«<cD0»C9CDOi0i-^0»0»e^OI^O'<«*«-ir«

C9 Ca CI 00 CO 00 CO CO 'V ^ «0 lO CO <0 t« 0» 1-1 CO 00«O6CO

f^ ^ i-> C« '^ <♦

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kO<0oooe^'<«*cDoe^iook'<<<ooOi»ot^i-i«-i »6.o> 00

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eo^-e^<oot«^<-OcocD1-4«-40ar«o»o^^*ooO'<f■OoOoo
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^ »0 OiCOCO<«*COC4*-i'*»«-^^Ot-«OC^»Ot-»OOt^<OeO

kOcot«o»i-4eokOoo — -^ooeoooio^udoc^co'^ooo)

C^CIWC«C0C0C0C0^'<*"«««»0i0C0t*«OC^»0-^^»P

•-•. ri »-« C<l CO 00

l^i-i»O<»M^a)Or-CiC0t^b-."^C0C0t-b-C^O000»

0S0&»O00"«*C^O0iOC000C0C000t^0a — •-^'«*OiOO

Ot-Mi-i00«i0C0»0-H0iCl»00i'*00'*00C0'**<»0»-*O

OiG^^t^<wooc>^t-cooo^-c^«©«ocO"*ooc^c^^O'*»o.

"* 0 r-; 05 r-< CO vO t^ 0 CO t- W Jf- "^ 5^ eo i* 00 OS C^ C^» l>

. oiMcioieococo'cO'^^ViOiOtfJt^oocii-J'v'o'^'oo

) — 1-IM CO CO

»»<»i-ioo»fli^40ooooco»ooou5r-»bcoioi^"^*oo
00'5»«c^coa5'^or^'«i'CO»fl>c^Ji«-eoeocoocOi-4C^O
to kO f "^-i^ ot>c^»0'-t"^'^-<eo\r5"^Tj40Q-4coo

t^Or»«Ot«-t-00e0 — COO"*!--— «-4'^'-<COOOOCOOa

•^<Ot-050C«'««»«t5-0 COt^ 1-1 CO .00 ^^O'«*C0OC0CM

woie»wcococoeo^"*'^»o»o»i-coo&»-H'n«osoot-

ri *-4 ^ Ol kO

QO^O*-4es]eO'<4«ocor-ao»o<-Ac^co^iOcor*opo»
cDcDt<-t*t*t«c*t«t<-t*t«t*oooooo 00 ao «.« 00 00 00

490

ALTERNATING CURRENT SIGNALING.

THE METRIC SYSTEM
TOGETHER WITH THE CUSTOMARY EQUIVALENTS

LCNEAR.

SQUAma.

MetTM (o F«et.

Kilometres
to Miles.

Square Metres
to Sq. Feet.

Hectares
to Acres.

2-
3-

4-
6-

(

7-
8-
9-

3.28083

6.56167

9.84250

13.12333

16.40417

19.68500
22.96583
26.24667
29.52750

0.62137
1.24274
1.86411
2.48548
3.10685

3.72822
4.34959
4.97096
5.59233

10.764
21.528
32.292
43.055
63.819

64.583
75.347
86.111
96.874

2.471
4.942
7.413
9.884
12.355

14.826
17.297
19.768
22.239

CVBIC.

Capacitt.

Wbiobt.

Cu. DecimetrM
to Cubic Inches.

Co. Metres
toCu. Yards.

Litres to
Quarts.

Kilocrammes U»
Pounds Avoirdupoia.

2-
3-
4-
5-

6-
7-
8-
9-

61.023
122.047
183.070
244.093
305.117

366.140
427.163
488.187
549.210

1.308
2.616
3.924
5.232
6.540

7.848

9.156

10.464

11.771

1.0567
2.1134
3.1700
4.2267
5.2834

6.3401
7.3968
8.4534
9.5101

2.20462
4.40924
6.61386
8.81849
11.02311

13.22773
15.43235
17.63697
19.84159

Customafy to Metric.

LiNBAB.

Square.

Feet to Metres.

Miles to
Kilometres

Sq. Feet to
Sq. Decimetres.

Acres to
Hectares.

3-
4-

«-
7-
8-
9-

0.304801
0.609601
0.914402
1.219202
1.524003

' 1.828804
2.133604
2.438405
2.743205

1.60935
3.21869
4.82804
6.43739
8.04674

9.65608
11.26543
12.87478
14.48412

9.290
18.581
27.871
37.161
46.452

55.742
65.032
74.323
83.613

0.4047
0.8094
1.2141
1.6187
2.0234

2.4281

,2.8328

3.2375

3.6422

CVBIC.

Capacity. '

Wbiobt.

Cu. Feet to
Cu. Metres.

Bushels to
Hectolitres;

Quarts to
Litres.

Avoirdupois Pounds
to Kilocrammea.

•i2- .
3-

7- '
8-

0.02832
0.05663
0.08495
0.11327
0.14158

0.16990
0.19822
0.22694
0.26485

0.35242
0.70485
1 .05727
1.40909
1.78211

2.11454
2.46096
2.81938
3.17181

0.94636
1.89272
2.83908
3.78544
4.73180

6,67816*
6.62452
7.67088
8.61724

0.45359
0.90719
1.36078
1.81437
2.26796

2.72160
3.17615
3.62874
4.08233

TABLES AND DATA.

491

TABLE OF DECIMAL EQUIVALENTS

Sths

16
ths

32
nds

64
ths

Decimal

•

sths

16
ths

•

nds

64
ths

Decimal

.015625

.515625

2
3

.03125
.046875

34
35

.53125
. 546825

4
5

.0625
.078125

36
37

.5625
. 578125

.09375
.109375

.59375
. 609375

8
9

.125
. 146325

40
41

,625
. 640625

10
11

. 15625
. 171875

42
43

. 65625
.671875

.1875

.6875

.203125

.703125

14
15

.21875
. 234375

46
47

.71875
. 734275

16
17

.25i
. 265625

48
49

.75}
. 765625

18
19

. 28125
. 296875

50
51

. 78125
. 796875

20
21

.3125
.328125

52
53

.8125
.828125

22
23

. 34375
. 359375

54
55

.84375
.859375

24
25

.375
.390625

56
57

.875
. 890625

26
27

.40625
.421875

58
59

,90325
.921875

28
29

.4375
.453125

60
61

.9375
.953925

.46875

.96875

. 484375

.984375

.5)

492

ALTERNATING CURRENT SIGNALING.

TRUNKING— SIZES AND CAPACITY

No.

Inside
Dimensions
of Groove

Outside

Dim.

Tr unking

Alone

Capping
Alone

Capacity

U.S.

&s.

No. 9
Single
Cond.

Wire
Cable

lH"x IH"

2J^ "X 3 K"

J^ "X 3 >i"

lH"x 2"

2J^"x 4K"

M "X 4 Ji"

2" X 3"

3Jg"x 6K"

1 H"x 6 >i"

2" X 6"

35i"x 7Ji"

15i"x 7%"

2>i"x 7"

5H"x 9H"

lj^"xl0^"

3>i"x 7"

6H"x 9M"

IH^'xlOH"

4>i"x 7"

75i"x 95i"

m"xlOH"

3Ji"xl2"

7%"xl5H"

IH"^IQH"

160

3 5i"xl6"

7Ji"xl9 5i"

lK"x20 5i"

210

4^"xl5H"

9>i"xl9M"

lH"x20H"

240

5H"xl9H"

9^"x23K"

1*A"^24H"

338

Note — The wire capacities given in the above table allow 25
per cent, spare space. The capacity for wires smaller than No.
9 as used in signal work, is considered to be the same as that
given for No. 9, there being no great difference in the wire diam-
eters; a No. 6 wire will take up about the same space as two No.
9 wires. Tnmking Nos. 4 and 16 are standard R. S. A. sizes.
Nos. 4, 20 and 16 cover grooved trunking, while the remaining
sizes are built up.

TABLES AND DATA.

R. S. A. GROOVED TRUNKtNC

^^f\

t'fa*i'<

fimOVED TRUNKING

Irsa

494

ALTERNATING CURRENT SIGNALING.

SQUARE

HEAD LAG SCREWS

Diameter

m
Ine&ee

%«

•%

Length.

■ —

Average Weight per Hundred |

m
Inehea

Lbs.

Lbe.

LbiL

4.2

6.5

9.2

13.0

• • • •

« • • •

4.7

7.1

10.0

13.8

• • « •*

• • '• •

• • • •

6.2

7.7

10.9

14.9

23.0

24.8

■ • « •

• I • •

6.7

8.4

11.8

16.1

24.5

27.3

• • • •

6.2

9.2

12.7

17.4

26.0

29.0

43.0

• • • -•

7.2

10.6

14.6

19.0

29.2

32.9

48.3

75.0

3V&

8.2

12.0

16.6

21.5

32.5

36.9

53 8

78.5

9.2

13.5

18.8

24.0

35.9

41.0

59.6

82.0

10.2

16.0

20.7

26.5

39.3

44 9

65.6

86.0

108

11.3

16.5

22.8

29.0

42.7

48.8

71.5

90.0

118.

6Mi

12.4

18.0

24.9

31.5

46.1

52.7

77.6

98.0

128

13.5

19.5

27.0

34.0

49.5

56.6

83.5

106.0

138

COMMON WIRE

NAILS

Size

Length

in
Inches

Diameter

Inches

Approx.

Number to

Lb.

Approx.

Lbs. per

1000

.072

876

1.14

.080

568

1.76

.100

316

3.16

.100

271

a.60

.113

181

5.53

2y4

.113

161

6.21

.131

106

9.43

.131

10.4

lOD

.148

14.5

12D

3V4

.148

15.9

16D

.162

20.4

20D

.192

32.3

30D

.207

41.7

40D

.225

65.6

50D

.244

71.4

60D

.263

90.9

TABLES AND DATA.

495

TABLE OF TURNOUTS FROM STRAIGHT TRACK
Gauob, 4 Fbbt, 8H Inches. Tbrow of Switch* 5 Irgbm

Lead-Dist.

Frog
Num-
ber

Frog

Angle

FPB

Length

Point

of Frog

to Toe

Length

Point

of Frog

to Heel

Length

of
Switch

RaU

Switch

Angle

BAC=:

TOO

Radius

Center

Line

OC-iga

of
Lead
Curve

Actual

Point of

Switch

RaU to

Actual

Point of

Frog AB

a i

W M

i d

§1 1

9-31-38

4- 0

7- 0

11-0

2-36-19

265.39

21-43-04

47.98

8-10-16

4- 5

8- 1

16-6

1-44-11

362.08

15-52-29

62.10

7-09-10

4- 9

8- 9

16-6

1-44-11

487.48

11-46-27

67.98

S-21-35

6-0

10- 0

16-6

1-44-11

605.18

9-28-42

72.28

6-01-32

6- 0

10- 0

16-6

1-44-11

695.45

8-14-45

76.71

5-43-29

6-^

10- 6

16-6

1-44-11

790.25

7-15-18

77.93

5-12-18

6-0

11-6

22-0

1-18- 8

922.65

6-12-47

04.31

4-46-19

6-6

12- 1

22-0

L-18- 8

1098.73

5-12-69

100.80

3-49-06

7- 8

14-10

33-0

0-52- 5

1744.38

3-174)1

133.28

3-34-47

8-0

16- 0

33-0

0-52- 5

1993.24

2-52-50

137.57

3-10-56

8-10

17- 8

33-0

0-52- 5

2546.31

2-14-31

146.51

2-51-51

9-8

19- 4

33-0

0-52- 5

3257.26

1-45-32

157.42

2-23-13

11-4

23- 2

33-0

0-52- 5

4886.16

1-10-21

177.22

496

ALTERNATING CURRENT SIGNALING.

¥ablb 09 onosdovERs

QAWn, 4 FuDf, 8V6 Inchxs. Throw of Switch, 5 Inches

- Total Lena

<^— U«d-

r^ 1 A^#l

-r—

Tuck Cttntets^^*"**-*^

Frog
/Number,

L9AD

dlstancib ca) between frog points for track
Centers Below

11'

12*

13'

14'

15'

16'

Feet

47.98

9.5

15.5

21.5

27.5

33.5

39.5

62.10

11.1

18.1

25.1

32.1

39.1

46.1

67.98

12.7

20.7

28.7

36.7

44.7

52.7

72.28

14.2

23.2

32.2

41.2

50.2

59.2

75.71

15.0

24.5

34.0

43.5

53.0

62.5

77.93

15.8

25.8

35.8

45.8

55.8

65.8

94.31

17.4

28.4

39.4

50.4

61.4

72.4

100.80

19.0

31.0

43.0

55.0

67.0

79.0

. 15

133.28

23.8

38.8

53.8

68.8

83.8

08.8

137.67

25.3

41.3

57.3

73.3

89.3

105.3

146.51

28.4

46.4

64.4

82.4

100.4

118.4

■ 20

157.42

31.6

51.6

71.6

91.6

111.6

131.0

177.22

38.0

62.0

86.0

110.0

134.0

158.0

^Frog
Number

TOTAL LbNOTH of

Crossover for Track Cbntebs Below

12'

13'

14'

15'

16'

Feet

105.5

111.5

117.5

123.5

129.5

135.5

. 7

135.8

142.3

149.8

156.3

163.3

170.3

148.7

156.7

164.7

172. t

180.7

188.7

158.8

167.8

176.8

185.8

194.8

203.8

9M^

166.4

175.9

185.4

194.9

204.4

213.9

171.7

181.7

191.7

201.7

211.7

221.7

. 11

206.0

217.0

228.0

239.0

250.0

261.0

220.6

232.6

244.6

256.6

268.6

280.6

290.4

305.4

320.4

335.4

360.4

365.4

300.4

316.4

332.4

348.4

364.4

380.4

321.4

339.4

357.4

375.4

393.4

411.4

346.4

366.4

386.4

406.4

426.4

446.4

.24

392.4

416.4

440.4

464.4

488.4

512.4

Nora. — JMstaniDe (A) beiwMn frog points
|>vtaoato=(trRok otntflf* ^ 2 zgauge) x (ng

based on f onnuls i
numbar.

TABLES AND DATA.

497

RAIL SECTIONS

A. R. A. RAILS— TYPE "A'

Weight

per

' D

Yard

•.

Lbs.

In.

in.

In.

23^,4

i%e

11%4

2y4

»%2

«%2

ini2

22f&2

«%2

i%6

•2%

*%4

3%9

11%2

2%o

5Vs

100

IMe

•^«

A. R. A. RAILS— TYPE "B"

Weight

per

B •

Yard

Lbs,

In.

4%e

2^6

8%4

S^He

4«6'a4

2iyo4

6%4

12%*

«%4

4%4

416,i6

21%2

U%2

2546

•^M

4%o

517/64

1«%4

2%o

4*%4

100

54V04

25%4

1%4

1*%4

22^2

%«

5%4

A: S. C. E. RAILS

Weight

per

Yard

In. ,

Lbs.

In.
4M6

In.

21VC4

In.

2y82

In.

4M6

UV64

2V4

1%2

. CO

4y4

21%4

*%4

ITb

«yo4

4y4

4T4o

2%2

1%2

21%2

4H6

21^82

i%o

ll%o

2%o

8VC4

: 75

41^0

28^04

2%2

li!%4

21%2

lt&2'

4l%e

.jBO

8%i

5?io.

2y4

,8-/64

,i?ro4

2%e

%«

2'^^4

80/^1

11%2

6%e

2«%4

' «;4e

*^v«..

2Hie

5%6

100

3%4.

•H2

.1*564

2%.

110

6^ 3i^is

'|a%2

.2%.

»%4

496 ALTERNATING CURRENT SIGNALING.

LOGARITHMS.

!• Theory. The power n to whith a fixed number, say
B. called the Base, must be raised in order to equal a given
number A is called the logarithm of A to the base B; thus if
B*^ = A, then n is the logarithm of A to the base B. When
10 is the base, as in the common or Briggs system, the logar-
ithm of 100 is 2. for 10^ = 100 and likewise the logarithm of
1000 = 3. In general

logxy= logx + log y- (0

log— ^ =a log X -- log y. (2)

log x** = n log X. (3)

For example.

logio 376.42 = log (100 X 3.7642)
= log 100 + log 3.7642
= 2 -H log 3.7642

The integral part of a logarithm is (Sailed the Charaderistic;
the fraction or decimal part is the Mantissa. The character-
istic of the log of a number greater tkan 1 is positive and 1 less
than the number of digits in its int^ral part; thus log 4580 =
3.6609. The characteristic of the logarithm of a decimal is
negative and numerically cyie greater than the number of
C3rpher8 immediately following the decimal point, but to avoid
writing a negative characteristic before a positive mantissa,
it is customary to add 10 to the characteristic and to indicate
that this added number is to be subtracted from the whole
logarithm; thus log 0.0045a = 3.6609 = 7.6609—10. The
standard log tables on the foUpwing pages give the mantissa
only, the characteristic of the nfimber-being easily determined
by the above rules.

2. Examples. Equations (I)^ (2^ and (3) respectively,
are used as the basis of multiplication, division and raising a
given number to a given power; for example.

Multiply 376.2 by 0.587

log 376.2 = 2 + 0.57541
log 0.587 = — 1 + 0.76863

= 1+1 .34404 by addition

= 2.34404

^nd from the tables the number whose log is 2.34404 = 220.8

TABLES AND DATA. 499

Divide 37.62 by 587

log 37.62 = I + 0.57541 = 1.57541

log 587 = 2 + 0.76863 = 2 + 076863

= — 2 + 0.80678 by sub-

tracticm and from the tables the number whose log is — 2 +
0.80678 = 0.06409.

500

ALTERNATING CURRENT SIGNALING.

COMMON LOGARITHMS

No.

00432.

00860

01283

*oi703

02H9

02531

02938

03342

03743

04139

04S32

04922

05308

05690

06070

06446

06819

07188

07555

07918

08379

08636

08991

09342

09691

10037

10380

10721

11059

II394

II737

12057

12385

12710

13033

13354

13672

13988

14301

X46I3

14921

15229

15534

15836

16x37

16435

16732

17026

17319

17609

17897

18x84

18469

18752

19033

19312

19590

X9866

20140

20412

20683

20952

21218

21484

. 21748

220x0

22271

22530

22788

2304s

23299

23552

23804

24054

24303

24551

24797

25042

25285

35537

25767

26007

26245

2648X

267x7

26951

27x84

27415

27646

27875

28103

28330

28SSS

28780

29003

29225

29446

296G6

29885

30103

30319

3053s

30749

30963

31X75

31386

31597

31806

32014

. 21

32222

32438

32633

32838

33041

33243

33445

33646

33845

•lAOAA

34243

34439

34635

34830

35024

352x8

354x0

35602

35793

35983

36173

36361

3^S48

3673s

36921

37106

37291

37474

37657

37839

38021

38201

38381

38560

38739

389x6

39093

39269

39445

396x9

39794

39967

40x40

4031a

40483

40654

408W

40993

4ri62

4x330

41497

41664

41830

4x99s

42160

42324

42488

42651

428x3

42975

43136

43296

.43456

436x6

43775

43933

44090

44248

44404

44560

44716

44870

4502^

45x78

45331

45484

45636

45788

45939

46089

46240

46389

46538

46686

46834

46982

47129

47275

47421

47567

47712

47856

48000

48x44

48287

48430

48572

48713

48855

48995

49136

49276

49415

49554

49693

49831

49968

50x05

50242

50379

SOSiS

50650

50785

50920

51054

51188

51321

51454

51587

•5I7I9

5x851

51982

52113

52244

52374

52504

52633

52763

52891

53020

53148

53275

53402

53529

53655

53781

53907

54033

54157

54282

54407

54530

54654

54777

54900

5S022

55145

55266

55388

55S09

55630

.5S750

55870

5S990

56XXO

56229

56348

56466

56584

56702

56820

56937

57054

S7»70

57287

57403

57518

57634

57749

57863

57978

S8092

58206

58319

58433

58546

58658

5877X

58883

58995

59106

59217

59328

59439

59549

59659

59769

59879

59988

60097

60206

60314

60422

60530

60638

60745

60853

60959

61066

61172

61278

61384

61489

6X595

61700

61804

61909

62013

62118

62221

6232s

62428

62531

62634

62736

62838

62941

63042

63x44

63245

63347

63447

63548

63648

63749

63848

63948

64048

64147

64246

6434s

64443

64542

64640

64738

64836

64933

65030

65x27

65224

65321

65417

65513

65609.

65705

65801

65896

65991

66086

66181

66276

66370

66464

66558

66651

66745

6683&

66931

67024

671x7

67210

67302

67394

67486

67577

67669

67760

67851

67942

68033

68124

68214

68304

68394

68484

68574

68663

68752

68843

68930

69020

69108

69196

69284

69372

69460

69548

6963s

69722

69810

69897

69983

70070

70156

70243

70329

7041S

70500

70586

70671

70757

70842

70927

71011

71096

71180

71265

71349

71433

7x516

71600

71683

7176;^

71850

71933

72015

72098

72181

72263

73345

72428

72509.

72501

72672

72754

7283s

72916

72997

73078

73158

73239

73319

73399 73480

73SS9

73639

73719

73798

73878

73957

TABLES AND DATA.

501

COMMON

LOGARITHMS

Ho.
55

9
74741

74036

741 15

74193

74272

74.1^1

74429

,74507

74585

74663

74818

74896

74973

75050

75127

7S204

' 7$28x

75358

7S434

75SII

7SS87

75663

75739

75815

75891

75966

76042

76117

7619a

76267

7634a

76417

76492

76566

76641

767IS

76789

76863

76937

77011

77085

77158

77232

77305

77378

77451

77524

77597

77670

77742

77«IS

77887

77959

78031

78103

7817s

78247

78318

78J90

78461

78533

78604

7867s

78746

78816

78887

78958

79028

79098

79169

79*39

79309

79379

79448

79518

79S88

79657

79726

79796

7986s

79934

80002

80071

80140

80308

80377

80345

80413

80482

80550

KnfiiS

80685

80753

.80821

8088R

80956

81023

81090

81157

81224

81391

81358

81424

81491

81557

81624

81690

81756

81823

81888

81954

8302O

82085

82151

82216

82282

82347

83412

83477

8>S42

82607

62672

82736

828CI

83866

82930

82994

83058

83123

83187

83250

83314

83378

83442

83505

83569

83632

83695

83758

83821

83884

83947

84010

84073

84136

84198

84260

84323

8438s

84447

84509

84571

84633

84695

84757

84818

84880

84941

85003

85064

8S"5

85187

85248

85309

85369

85430

85491

85551

85613

8S672

8S733

85793

85853

85913

85973

86033

86093

86153

86213

86272

86332

86391

86451

86510

86569

86628

86687

86746

86805

8G864

86923

86981

87040

87098

87157

87215

87273

87333

87390

8T448

87506

87564

87621

87679

87737

87794

87853

87909

87966

88021

88n8i

88138

88195

88352

88309

88366

88433

88479

88536

88502

88649

88705

88761

88818

88874

88930

88986

89042

89098

89153

89209

89265

89320

89376

89431

89487

89S42

89597

89652

89707

89762

89817

89872

89927

80983

90036

90091

90145

'90200

90254

90309

90363

90417

90471

90535

90579

90633

90687

90741

90794

90848

90902

90955

91009

91062

9111S

91169

91233

91275

91328

91381

91434

91487

91540

91592

91645

91698

91750

91803

9185s

91907

91960

92012

93064

92116

92168

93330

92272

92324

92376

92427

92479

92531

93582

92634

92685

92737

93788

92839

92890

92941

92993

93044

93095

93146

93196

93247

93298

93348

93399

93449

93SOO

93S50

93601

93651

9370I

93751

93802

93852

93902

939SI

94001

94051

94101

94151

94200

94250

94300

94349

94398

94448

94497

94546

94596

94645

94694

94743

94792

04841

94800

94939

94987

95036

95085

9S133

95182

95230

95279

95327

95376

9S424

95472

95S20

95568

95616

95664

95712

95760

95808

95856

95904

9S95I

95999

96047

96094

96142

96189

06336

96284

96331

9»

96378

96426

96473

96520

96567

96614

96661

96708

96754

96801

96848

9689s

96941

96988

97034

97081

97127

97174

97220

97266

97312

97359

97405

97451

97497

97543

97589

97635

97680

97726

97772

97818

97863

97909

97954

98000

98045

98091

98136

98181

98227

98272

98317

93363

98407

98452

98497

98542

98587

98633

98677

98721

98766

98811

9885s

98900

98945

98989

99033

9^78

99122

99166

99211

9925s 99299

99343

99387

99431

99475

99519

99563 99607 996SI 99694 99738

99782

99825 1 99869

99913

999S6

502

ALTERNATING CURRENT SIGNALING.

THERMOMETERS

CENTRIGADE AND FAHRENHEIT

Rises in temperature in electrical apparatus, such fdr example as trans-
formers and generators, are specified in Centigrade degrees and in (act all sci- .
entific heat measurements are carried out on this basis. The fundamental
•cale readings of the Centigrade thermometer as compared to the Fahren-
heit thermometer are as follows: —

Boiling Point Freezing Point

Centigrade 100° 0°

Fahrenheit 212° 32°

Hence to transpose from one scale to the other

po = /9 X CO \ + 32° and C° = 5 /F°— 32°>

COMPARISON BETWEEN

CENTIGRADE AND FAHRENHEIT
SCALES

Pahr.

Cent.

Fahr.

Cent.

Pahr.

Cent.

Fahr.

Cent.

Pahr.

Cent.

-5

-ao.55

-11.66

-2.77

6. II

15.00

-4

— ao.oo

—II. II

—2.22

6.66

1555

-3

-IQ.44

-I0.5S

-1.66

7.22

16.11

—2

-18.88

—10.00

—1. 11

7.77

16.66

—I

-18.33

- 9.44

- -55

8.33

17.22

Z«ro

-17.77

- 8.88

Zero

8.88

17.77

—17.22

- 8.33

+ .55

9.44

18.33

-16.66

- 7.77

I. II

10.00

18.88

—16.1i

— 7.22

1.66

10.55

19.44

-15. 55

- 6.66

2.22

11. II

20.00

—15.00

- 6.H

2.77

11.66

20.55

-14.44

- 5. 55

3.33

12.22

21. II

-13.88

— s.oo

3.88

12.77

21.66

-13.33

- 4.44

4.44

13.33

22.22

-12.77

- 3.88

5.00

13.88

22.77

—12.22

- 3.33

555

14.44

^.33

TABLES AND DATA.

503

COMPARISON BETWEEN CENTIGRADES AND FAHRENHEIT

SCALES.— Continued.

Pahr. Cent.

75
76
77
78

79
80
8x
82

83
84
85
86

87
88

89
90

91
92

93
94

95
96
97
98

99
zoo

lOI
102

103
104

IQS

106

107
108

109

no
ixi

ZZ2

U3
"4

"5
iz6
117
118

119
120

23.88

24.44
25.00

35-55

26.IX
26.66

27*22

27-77

28.33
28.88

29.44
30.00

30-55
3I-IX
31.66
32.22

33.77
33.33
33.88
34.44

35.00

35.55
36.11
36.66

37.22
37.77
38.33
38.88

39.44
40.00

40.55
41. iz

41.66
42.22
42.77
43.33

43.88

44.44
45.00

45.55

46. IX

46.66

47.22
47.77

48.33
48.88

Pahr.

I2X

122
123
124

X2S
126

127
128

129
130

131
132

133
134
135
136

137
138

139

140

141
142

143
144

145
146

147
148

149
ISO
X5I
152

153
154
X55
156

157
158

159
160

161
163
163
164

X6S
166

Ceot. Pahr.

49.44
50.00

50.5s
5X.XI

51.66
52.22
52.77
53.33

53.88

54. 44
55-00

55-55

56.11
56.66
57.22

57.77

58.33
58.88

59 44
60.00

60.55
6x.zi
61.66
62.22

62.77
63.33
63.88

64.44

65.00

65. 55
66.11
66.66

67.22

67.77
68.33
68.88

69.44
70.00

70.5s
71. XX

71.66
72.22
72.77
73.33

7388
74.44

67
68

69
70

71
72
73
74

75
76
77
78

79
80
81
82

84
8S
86

87
88

89
90

9X
92

93
94

95
96
97
98

199
200
201
202

203
204
205
206

207
208
209
2ZO

2IX
212

Cent. Pahr.

75.00

75.55
76. XX
76.66

77.22
77.77
78.33
78.88

79.44
80.00

80.5s
81.XX

81.66
82.23
82.77
83.33

83.88

84.44
85.00

85. 55

86.11
86.66
87.22
87.77

88.33
88.88

89.44
90.00

90.55
91. II
91.66
92.22

92.77
93.33
93.88

94.44

95.00

95.55
96.11
96.66

97.22
97.77
98.33
98.88

99.44
xoo.oo

213
214

2X5
2X6

217
218
219
220

221
222
223
224

325
326
227
328

229
330
331
333

333
334
23s
336

337
338
339
240

241
242

343
344

345
346

347
348

349

3S0

35X
353

353
354

355

356

as7

358

Cent.

00.55
01. II
01.66

03.22

02.77
03.33
03.88

04.44

05.00

0S.S5
06. XX

06.66

:o7.22

07.77
08.33
08.88

09.44

10.00

10.55

IX. XX

11.66

12.32
12.77
13.33

13.88

14.44
15 00

15.55

V^.U
16.66
17.22

X7.77

18.33
18.88

19-44
20.00

30.55

21. XI

21.66

22.23

22.77
33.33
23.88

34.44
3S.00

25-55

Pahr. Cent

359
260
261
363

363
364
36s
366

367
368
369

370

37X

373

374

375
376

377
378

379
360
28X
283

383
384
285
286

287
388
389
390

391
393
393
394

395
396

399

300
400

600

800

1000

X36.XI

136.66
137.33
137.77

X38.33
128.88

129.44
130.00

130.55
131. XI
131.66
133.33

X33.77
133*33
133-88

X34-44

135.00

135.55
136. II
136.66

X37.33
X37.77
138.33
X38.88

X39..44
140.00

140-55
I4I.IX

X4X.66
143.33
X43.77
X43.33

X43-88

144.44
X45.00

145.55

X46.XX
146.66

147.33
X47.77

X48.33
X48.M
304.44
3X555

436.66
537.77

TABLES AND DATA.

505

R. S. A. SIGNAL SYMBOLS.

Ground
Mast.

7^^

Ground Mast with
Bracket Attachment.

r- — - I- '

Offstt
Bracket Post.

V ' 'r '

I I

■ I

BftACKCT

Post.

suspcnoco
Mast.

Ring eWolosed
characteristics
mean u6ht signal

ONLY.

Smash Swnal,

Pot Signal,

Disc Sishals.

<S) @ © ®

Home Home Distant Distant Double

Proceed. Stop. Proceed. Caution. Functioned.

J-—-,

L...J
I

Present Signal to be Removed.

Present Signal to Remain.

Relation OFTMESKNALTOTHE'niACKANOTICDfRCCnON OFTklAPFiC

"I Right Hand Locations.

Right Hano Signal.

Left Hand Sisnal.

Left Hand Locations.

■i

Ri€HT Hand Signal

Left Hano Signal.

506

ALTERNATING CURRENT SIGNALING.

R. S. A. LOCATION SYMBOLS.

Insulating Rail Joints.

■♦■

■f-

Track Cipcuits in.
Both Dircctions.

Track Circuit on
Left , None on Right.

Track Circuit on
Right, None on Left.

Impeoance Bond.
CD

Traffic Direction.

Station. Grossing Gate.

Track Pan.

Signal Signal SuB-Statkm .

Power Station. ^

4:::t4

Tunnel. Bridge or Vuouct. Draw Bridge. Lift Bridge.

NOTE: State wnitmii Decic. HAtr-THMutH w Tmowm Bmocc.

Mile Post.

OvMHEAO

Bridge.

Signal
Baipce .

Highway Railway Prorosco Railwmy

CR0SSIM« CR0SSIN6. CROSSING.

NOTC:SKarr «nctmu Stiam m Clcctm; RvCwssmo.

o— ^

Mail Crane. Water Tank. Water Column. Track Instrument. Torpedo Machine.

Train Stops.

4 6 ^

Stop.

Clear.

NON -Automatic Slotted. Semi- Automatk.

Mechanical. Power. Automatic

Power Switch
Machine.

Insulated
Switch Rod.

Torn-Out
AND Switch Stand.

Electric
Switch Lock.

TABLES AND DATA.

507

R. S. A. LOCATION SYMBOLS.

[13-

CAPACITY

Relay Box. Junction Box. Terminal Box. Lightning Arrester

Box.

(D-

CapaCitv

Battery Chute .

CAPACITY -

RCLAV BOK CAPACiTV
CHUTt CAPACiTt

RELAY Box AND Post. Battcay Chute, Rf lay

Box ANO Post Combined.

NOTE : Type of inoicato«

TO BE covered BY

general note

Switch Box Location. Switch Indicator.

■ ?

Switch Indicator
ANO Switch Box.

A
6

Cable Post With One
Only. Indicator.

With Two With Relay With Relay With Relay
Indicators. Box. Box and One Box and Two

Indicator . Indicators .

M
S
M

ABOVE Surface .

Half Above Surface.

Highway Crossing Bell.

> Battery Shelter.

Below Surface.

(FMucs MotCKre CAMcmr)

"B"

Track Battery

508

ALTERNATING CURRENT SIGNALING.

R. S. A. TRACK SYMBOLS, ETC.

Interlocked Switches and Derails.

dwrrcH-Scr for TuRN-Ovf«

Derail- Point TVpe-Deraiung .

Switch- Set for Straisht Track.

Derail- Poimt Type-Nom-Derailimg .

Derail «-LiFTm6 Rail Type -Derailing.

Derail- Lifting RailTypc-Non-Derailino.

Derail - Lifting BlockTypc -Derailing . Derail- Lifting BlockType-Non-Derailing..

NOTE: NoN-uiTERLOCKeo smitcmes mo kvmls Tt ec Shown

SAMC AS VtOtt CXCf PT ShMMM M T1|iAN6L» OMlTrCO.

Runs

6F CONNECTlON$.

Pipe-Wire (Mecn),

Wire Duct.

•

COMPRcssEO Air.

p*Mariia«*iw • «

PiPE-WiHE AND Duct.

Pipe -'Wire and Air.

Duct ano Air.

Pipe -Wire, Duct and Air ,

Man-hole.

ViBdJUBSAaa

Detector Bar.

ai.

Bolt LOCKS.

I-Way.

r^^^ ^

60LT locked Switch.

S.L.M.-SllVlTCtt AiLOCK MOVEMENT.

RP.L.*Facin6 Point Lock,

HiAyV

Compensator.

Arrow Indicates Direction
OF Movement of Pipe Line-
Normal to Reverse.

EEh

CRANKS.

I-Way,

2-Wor.

Oil ENaosED Pipe Line , 3-Ww._

TRACK

"^1 Interlocking OR Block Statkm. ksia

rfM SMWMOnCUriVEmiTNM OF STVm.OnMTM and TRACK. k^±J

Operator Facing Track . Operator wrrM Back to Track.

NOTE: Unless oTMEiiwisi speofico on Plan it wia be assumed that where an

MfTCRLOCKEO SKMAL IS SHOWN CLEAR OR A DERAIL SHOWN IN N0N-OERAIUN6

POSITKM TNE CONTROaiMO LEVER IS REVERSED, AND THAT ALL OTHER LEVERS ARE NORMAL.

TABLES AND DATA.

R. S. A. LEADOirr SYMBOLS, ETC

EXH-AMWieW

16 Shaft Leu-out^

Cmi« Lead-out.

Defuctms Bar lkad-wt.

510

ALTERNATING CURRENT SIGNALING.

R. S. A. SYMBOLS FOR RELAYS, ETC.

ElEMCNTS OF SVM80LS T^
TO M COMSINCO AS J— L
NECCSSARY. ±L

i,i

4. .A

▼•-»

i : : !

i" f f >

?**T y^"^ ^"^T ^-^^
• • • • • t i I
I I • • I I II

^••4 4..* A..k 4..h

-o

^••* --^ -tr-x

J^ 4.-1 titl
"J?! -O-

:x; I on

♦It:!

•T ^— r ^'

INOIGATOIIS AND LOCKS .

D.C.EUCntO MAGNET.

A.C.EiccTRo Magnet.

COILENEROlZeO Oft Di-ENEROIZED.

NcuTML Front Contact -CuncoMOpeN.
NEimuL Back Contact - Closio or Opkn .

J. Polarized Armature - With Contacts .

3 - Position ARtMTURt - With Contacts .

High Current Contact.

Magnetic Blow-*put Contact.

Bell Attagmment.

I^BU WiNOMO-SKCiFY IP DirfERCNTlAL.

Slow Acting .

DiscTvre Indicator. OsOihInvisiole. •*DiscVi$ibu.

Semaphori Type Indicator. P"-3-Position.

Wire Wound Rotor.

Stationary Winoini. ;!.^*Hi6N V0lta6e Wiiome.

Cleotrjc Lock- Snow Segments for Lever in Normal
Positioh •

(see Hf XT pace for examples of COMMNATIOIIt.)

TABLES AND DATA,

511

R. S. A. SYMBOLS FOR RELAYS, ETC

-o

M
JJ.

JJ.

Relays , Indicators and Locks.

Examples op Combinations.

D.C. RELAY- NEUTHAi,- Energized -

ONE InoCpcnknt Front Contact Closed-
Oiic Independent Back Contact Open .

D.C.RELAY- Polarized - Energized -

Two OOMBIJIATION FRONT AND BACK NEUTRAL CONTACTS*
Two POLARilZED CONTACTS CLOSED «-

Two Polarized Contacts^ Open.

0.0. INDICATOR - Semaphore Tvpe- Energized -
ThRce Front ContactI Closed »
Bell Attachment .

D.C.INOICATOi^ - Semaphore Type - Arm Horizontal -

Energized- Without Contacts.
NOTE : lNl^Toia(illl rbkaters) wtthovt contacts should be shoivn

Wihri JtRMAIMtES to MOWATf WHETHER -ENlMiZCO OR K-fNCR-
CIZGO«

A.OrRELAY- One Energizing Circuit Type (Swole Phase)
ENERiftiZEO- One Front Contact.

A.C.RELAY-Tw6 Energizing Circuit Type- Energized «-
Wire Wound Rotor -
Two Neutral Front Contacts .

A.C. relay-Two Enerc(Z)n6 Circwt Type- Enkroized —
Wire Wound Rotor —
TWO Polarized Contacts.

A.C relay-Two Energizing Circuit Tvpe- Energized-
Stationary Windings —
One Neutral Front Contact-.
Two 3- Position Contacts.

D.C. INTERLOCKED RELAY.

D.C. ELECTRIC BELL.

DESMNATI RU<|TANCC W OrtMS iP all O.C.ReuWS, MPICAT9IIS AND LOCKS.

512

ALTERNATINC CURRENT SIGNALINa

R. S. A. SYMBOLS FOR LEVER CONTACTS

Circuit Controllers Operateo bt Levers.

' Use either Letter System or Graphic System .

' LEVERS WITH Extreme End Positun as Normal.

N-FuLL Normal Position of Lever
B -Normal Indication Position.
C-Central Position.
D-Reversc Indication Position.
R-Fuu. Reverse Position.

LETTEII
SYMBOL.

N B C D R

-(D-

-(£>■
-(£)-

-(£>
■%■
■%■
-(g)-

■%-
-<§>-

-(g)-

•#-

-%-

-#-

-%-

I
I
I
I
I
I
I
I
I
I
I
I

t
I
I
I
I
I
I
I

■H+

lY.

•MPMC
SITMML.

-:v

TSr

Levers with Middle Position as Normal .

N- Normal Position.
L-Full Reverse Position to the Left.
B-lNOiCATioN Position to the Left.
D -Indication Position to the Right.
R-Fua Reverse Position to the Right.

LETTER
SVMML.

-®-t

-®-

-<§>

-®r

-%-

-%■

-%-

-%■

-®-

■%-
-@-

■%-
■%-
-®-
■%-
•%■

-(g>-

B N D

'GRAPHIC
SYMBOL.

■^
■^

^
^

igr

%■

-#■

NOTE: Heavy horizontal unes moiute portion of cycle of lever twouch wnicm chgwt is aosco.

TABLES AND DATA.

R. S. A. SYMBOLS FOR SIGNAL CIRCUIT CONTROLLER

Circuit Controllers Operated by Signals.

UPPER qUADRANT. LOWER (jUAORANT.

Closco at Q Only,

3 -Position
Signals.

60*-70*0R
75* Signals.

Closed.
Open.

%-••

Closed

o i \J

4T 45 Only. #v-*^

Closed at 90 Only,

o •

Closed 0 tQ 45

Closed 45 to 90

Closed at 0* Onlv.

Closed ih'Cl^r
posiTKM OnlV*

Circuit Contmller Operated by Lockmo

Switch Circuit Controller.; Mechanism of a Switch Movement.

♦->-♦

Closed.
Open.

Bridge Circuit Controller.

Pole Changing Circuit Controller J

Spring Hand Key or Push Button.

_J^

Circuit Switch.

ALTERNATING CURREm' SIGNALING.

R» S*- A. SYMBOLS FOR TIME RELEASES* ETC«

Mmwml Time Rclcasc.

(CLECTRIC)

Manual Time Releajc .

(eLECTRO-MCCHAN*L.)

AuTONwnc TtMC Release .
(electric)

Floor Push.

EMEReENGY RELEASE

(electric)

LATCH Contact.

OPEN. closed.

Track Instrument Contact.

SfS^^

Knifi Switcmis.

<> 6 6

(> <> <)

flfHEOSTAT. Single Pole. Double Pole. SinguPole. Double Pole.
Single Throw. Double Throw.

OmcK Acting Circuit Controlurs may be Distinguished by the Letter 9"

0 0

Fixed Resisiance . Variable Resistance.

Fuse.

— nmm'

Impedance without
Iron Cone.

000000

Impedance witji
Iron Core

Condenser.

TABLES AND DATA.

545

R. S. A. SYMBOLS FOR BATTERIES, ETC.

Battery.

A.C.TERMINAI.S.

D.CTERMINAI.S.

Cells in Multiple. Cells m Series. o^._,^,. '

Specify Typc and Number of CaLS . kectw-i ek .

H StCaNOARV. 2-OI> MOM 3CC0NQMIIS.

Transformers.

O-Ory Battery.
G ■ Gravity »»
P • POTASH »»
S " STORAfiE «*

EXAMPLES: I$P,I0S,ETG.

(M)

O.G.MOTOR.,

AMMETER .

<s)

D.C.6ENERAT0R.

A.C.MOTOA.

(mm|) #-(|)

A.C.6ENERAT0R. OX.-O^.MflTOR-GEHERATOR. AJC.-O.C. MOTOR- e««"ATO«.

Voltmeter.

-®- 1^

Wattmeter. Telephone.

SlNOLE. OOUSLE.

INCANOESCENT LAMP. LtOHTNINO ARRESTER. TCRMWAtS.

Wires Cross .

Wires Join.

Grouno.

" Common " Wire .

Other than " Common" Wire .

Track Circuit Wire.

Direction of Current.

516

ALTERNATING CURRENT SIGNALING.

R. S. A. PORCELAIN TERMINAL BLOCK

^S^TlillL

i [T]

10564 CONNECTOR

( BRASS- N0.I8 Bw&S.GA.)
IO703-v_^W02 ^WnLr'UnOA

lOTOS BMOINo POST OOMPv«

4H0LES

I0S6I KMELAIN BASE

( REVCRSIBUE )

I0S62 CONNCCTOir

(BRASS- NO. le BAS.6A.)

8561

10563 ASSEMBLY

JL^J.

2 3

J L

L WITH COMPOUKD'

4
J

SCALE OF MCH((

NQTE: WHEN QROERWe APMRAIVS

OR mrrs shown on this k/m

GIVE NUMBER AND NAME APKAR-
ING M LAII6C TYPE.

T — r

TERMMAL BU)CKS

( OrnULS AND ASSEMBLY )

I iWI9l5IM-l-BMii>g5g

TABLES AND DATA. 5l7

- „ - ■ ■ IX I ■ -- . I ■ I .1 ^ I ■ ■ ■**

SPECIFICATIONS FOR PORTLAND CEMENT CON-

CRETE. (R. S. A.)

1 • General. These specifications are for making concrete
as used in signal construction.

2. Cement. Cement shall be Portland* either American

or Foreign » which will meet the requirements of the

specifications.

3. Sand. Sand shall be clean, sharp, coarse, and of grains
varying in size. 1 1 shall be free from sticks and other foreign
matter, but it may contain clay or loam not to exceed five (5)
per cent. Crusher dust, screened to reject all particles over
one-fourth (1-4) inch in diameter, may be used instead of sand
if approved by the Elngineer.

4. Stone. Stone shall be sound, hard and durable,
crushed to sizes not exceeding two (2) inches in any direction.
For reinforced concrete, sizes usually are not to exceed three-
fourths (3-4) inch in any direction, but may be varied to suit
character of reinforcing material.

5. Gravel. Gravel shall be composed of clean pebblea of
hard and durable stone of sizes not exceeding two (2) inches
in diameter and shall be free from clay and other impurities
except sand. When containing sand in any considerable quan-
tity, the amount of sand per unit of volume of gravel shall be
determined accurately, to admit of the proper proportion of
sand being maintained in the concrete mixture.

6. Water. Water shall be clean and reasonably dear,
free from sulphuric acid or strong alkalies.

7. Measure. The unit of measure shall be the barrel,
which shall be taken as containing three and eight-tenths (3.8)
cu. ft. Four (4) bags containing ninety-four (94) pounds of
cement each shall be considered the equivalent of one (1)
barrel. Fine and coarse aggregates shall be measured sepa-
rately as loosely thrown into the measuring receptacle.

8. Density of Ingredients.

(a) For pipe carrier foundations and reinforced concrete,
a density proportion based on 1 :6 is recommended, i.e., one ^

5W ALTERNATING CURRENT SIGNALING.

- ' - *

(I ) part of cement to a total of six (6) parts of fine and coarse
aggregates measured separately.

(b) For signal and other foundations made in place a den-
sity proportion based on 1 :9 is recommended, i.e., one (1 ) part
of cement to a total of nine (9) parts of fine and coarse aggre-
gates measured separately.

9* Mixing.

(a) Tight platforms shall be provided of sufficient size to
accommodate men and materials for progressive and rapid
mixing. Batches shall not exceed one (1 ) cu. yd. and smaller
batches are preferable.

(b) Spread the sand evenly upon the platform, then the
cement upon the sand, and mix thoroughly until of an even
color. Add all the water necessary to make a thin mortar and
spread again; add the gravel if used, and finally the broken
•teller both of which, if dry, should first be thoroughly wet
down. ' Turn the mass with shovels or hoes until thoroughly
incorporated, and all the gravel and stone is covered with
mortar; this will probably require the mass to be turned four
(4) times.

(c) Another approved method, which may be permitted at
the option of the Elngineer in charge, is to spread the sand,
then the cement and mix dry, then the grave or broken stone,
i^d water and mix thoroughly as above.

. : (d) A machine mixer may be used whenever the volume of
work will justify the expense of installing the plant. The nec-
essary requirements for the machine will be that a precise and
regular proportioning of materials can be : ontroUed and that
the product delivered shall be of the required consistency and
thoroughly mixed.

10. Consistency.

The concrete will be of such consistency that when dumped
in place it will not require much tamping. It shall be spaded
down and tamped sufficiendy to level off, and the water should
rise freely to the surface.

11. Forms.

(a) Where necessary, forms shall be well built, substantial
and unjrielding, properly braced, or tied together by means of
%^ yntse or rods, and shall conform to lines given.

TABLES AND DATA. ^r^

(b) For all important work» the lumber used for ftice fvbric
•haD be dressed on one (1 ) side and both edges to a unifomm
thickness and width, and shall be sound and free from loose
knots, secured to the studding or uprights in horizontal linea.

(d) Where comers of the masonry and other projectioas;
liaUe to injury, occur, suitable moldings shall be placed in thft
angles of the forms to round or bevel them otf.

(e) Lumber once used in forms shall be cleaned before being
used again.

(f) The forms must not be removed within thirty-six (36)
hours after all the concrete in that section has been placed.
In freezing weather they must remain until the concrete has
had a sufficient time to become thoroughly hardened.

(g) In dry, but not freezing weather, the forms shall be
drenched with water before the concrete is placed against
them.

12. Disposition.

(a) Elach layer shall be left somewhat rough to insure bond-
ing with the next layer above; and if it be already set, shall be
thoroughly cleaned and scrubbed with coarse brushes and
water before the next layer is placed upon it.

(b) Concrete shall be deposited in the molds in layers of
uniform thickness throughout.

(d) In no case shall work on a section stop within eighteen
(18) inches of the top.

(e) Concrete shall be placed immediately after mixing an0(
my having an initial set shall be rejected.

13. Facing.

(a) The facing will be made by carefully working the
<:oarse material back from the form by means of a shovel bar
or similar tool, so as to bring the excess mortar of the concrete
to the face. • '»

(b) About one (1) inch of mortar (not grout) of the same
proportions as used in the concrete may be placed next to die
forms immediately in advance of the concrete.

520 ALTERNATING CURRENT SIGNALING.

' I J ■ ■■

14. Finishing.

(a) After the forms are removed, which should generally be
as so<m as possible after the concrete is sufHciently hardened,
any.sknall cavities or openings in the face shall then be neatly
filled with mortar. The entire face shall then be washed with
a thin grout of the consistency of whitewash mixed in the
sanie proportion as the mortar of the concrete. The wash
shall, be applied with a brush. The earlier the above opera-
dons are performed the better will be the result.

(b) The top surface of all crank, compensator, well hole,
lock, dwarf and high signal foundations shall be rubbed smooth
by hand and shall be true to grade and line.

15. Waterproofing. Where waterproofing is required, a
thin coat of mortar or grout shall be applied for a finishing coat
upon which shall be placed a covering of suitable waterproof-
ing material.

16. Freezing Weather. Concrete to be left above the
surface of the ground shall not be constructed in freezing
weather, except by special instructions. In this case the sand,
water and broken stone shall be heated, and in severe cold,
salt shall be added in proF>ortion of about two (2) p>ounds per
cu. yd.

17. Reinforced Concrete. Where concrete is deposited
in connection with metal reinforcing, the greatest care must
be taken to insure the coating of the metal with mortar, and
die thorough compacting of the concrete around the metal.
Whenever it is practicable the metal shall be placed in position
first. This can usually be done in the case where the metal
occurs in the bottoms of the forms, by supporting the metal on
transverse wires, or otherwise, and then flushing the bottoms
of the forms with cement mortar, so as to get the mortar under
the metal, and depositing the concrete immediately after-
ward. The mortar for flushing the bars shall be composed of
one (1 ) part cement and two (2) parts sand. The metal used
in the concrete shall be free from dirt, oil. or grease. All mill
scale shall be removed by hammering the metal, or preferably
by pickling the same in a weak solution of muriatic acid. No
•alt shall be used in reinforced concrete when laid in freezing

TABLES AND DATA. 521

HOW TO REMEMBER THE WIRE TABLE

By Chas. F. Scott.

Reprinted by permission of tlie Electric Journal.

The wire table for the B. & S. gage copper wire has a few
simple relations, such that if a few constants are carried in the
memory the whole table can be constructed mentally with
-approximate accuracy.

Resistance. A wire which is three sizes larger than
another wire has twice the weight and half the resistance.

No. 10 wire has a resistance of I ohm per thousand feet;
No. 7 wire which is three sizes larger, has .5 of an ohm per
thousand feet; No. 4 wire, which is three sizes larger thcok No.
7, has .25 of an ohm; No. 13 wire, which is three si es smaller
than No. 10, has 2 ohms; No. 16 wire, which is three sizies
smaller than No. 1 3. has 4 ohms. It is easy, therefore, know-
ing the resistance of No. 10, to find the resistance of No. T ,
No. 4, No. 1 and No. 000; also of No. 13, No. 16, No. 19. etc.

A wire which is ten sizes larger than another wire has tct
times the weight and one-tenth the resistance.

As the resistance of No. 1 0 is I ohm per thousand feet, the

resistance of No. 0 is . 1 of an ohm, and the resistance of No. 20

wire is 10 ohms, as the resistance of No. 4 is .25 of an ohm,

the resistance of No. 14 is 2.5 ohms, and of No. 24, 25 ohms.

.. In the following table the first column contains the sizes

of wire which differ from one another by three sizes. Th«

.resistance of each wire in this column is seen to be twice that

. of the next larger size, and one-half that of the next smaller

size. There is, therefore, no difhculty in remembering this

column. In the second division of the table, the wires are

tjen sizes smaller than those in the first division; thus No. 1 1

corresponds to No. I and the resistance is ten times as great.

lijL the third division of the table, the wires are ten times

fl^g^r |:han those in the first division; thus No. 0 corresi>6nds

jS4^f,th No. 1 0 and the resistance is one- tenth as great.

No. 1

Ohms

Size

Olims

Size

Ohmt

.125

No. 11

1.25

No. .4.

.25

No. 14

2.5

•

No. 7

No. 17

No. 0000

.05

">?J8?iS'

1
"2

No. 20
No. 23

10
20

No. 0
No. 3

.1
.2

. No. 19

^ . 4 .

No. 26

, 40

No. 6

No. 29

No. 9

►'2r;Noi 22.-

" 16

No. 32

160

No, 12

1,6

.> Vq.25

No. 35

320

No. 16

3.2

522 ALTERNATING CURRENT SIGNALING.

From this table several new relations may be observed.

If the wire is one size smaller, the resistance is 25 per cent,
greater. For esLample: Compare No. II with No. 10, No.
12 with No. II. No. 13 with No. 12. etc.

If the wire is two sizes smaller, the resistance ia 60 per cent,
greater. For example: Compare No. 12 with No. 10, No.
16 with No. 14, No. 15 with No. 13.

If the wire is one size larger, the resistance is 80 per cent, of
that of the smaller wire. For example: Compare No. 9
with No. 10. No. 10 with No. 1 1.

- ' Ff the wire is two sizes larger, the resistance is 63 per cent.
Bf^that of the smaller wire. For example: Ccnnpare No. 1 1
^th'No. 13, No. 4 with No. 6.

'^ From the foregoing the following are the mtioe ci resistance
l^tween wires of consecutive sizes:

.50, .63, .80. 1.00. 1.25, 1.60, 2.00

Weight. The weight of a wire is inversely proportional to
its resistance. Therefore, the forgoing relations are the same
for weight as for resistance, excepting that the weights in-
crease as the size of the wire increases, instead of diminishing.
The waghts of successive sizes of wire, therefore, bear the fol-
lowing relation, beginning with the smaller wire:
: .50. .63, .80. 1.00. 1.25. 1.60. 2.00
^ If the weight of any size of wire is known, it is, therefore,
seen that the weight of the next larger size is 25 per cent,
greater; the weight of the second larger size is 60 per cent.
mprf^.^80.. the weight of the sixth larger size will be four times
^^reat, and the weight of the tenth larger size will be ten
^gpf^ as great. The weight of the third larger size is double.
' I The weight of 1 ,000 feet of No. 1 0 copper wire is 31.4
pounds. Therefore, the weight of No. 7 wire is 62.8 pounds;
the weight of No. 0 wire is 314 pounds. The weight of No.
^ wire is 100 pounds per thousand feet, which is a convenient
figure to remember. The weight of No. 2 wire is. therefore,
200 pounds, and the weight of No. 00 is 400 pounds.

Area. The area of No. 10 wire is approximately 10.000
circular mOs (more precisely 1 0,380). The area is proportion-
al to the weight. The area of No. 7 wire is, therefore, about
20,000 circular mils, of No. 0 wire 100,000, and of No. 0000
wire 200,000. The precise area of No. 10 wire is 10.380 mr-

TABLES AND DATA. 5»

jm^mmmmmmmm^^^t^mmmmmm^ ii ii i i i • ■ i-r -T.

cular mils. Taking this figure (or easy calculation as 10,400»
and following the process above indicated, the area of No.
0000 wire is found to be 206,000, which is very nearly 21 1 ,600
the figure in the wire table.

Diameter. The diameter of No. 1 0 wire is approximately
0.10 inch (more precisely 0.102). The diameters follow the
same ratio as the circular mils and weights, except that this
ratio applies to alternative sizes. Therefore, the sixth smaller
size has half the diameter, and the twentieth smaller size has
one- tenth the diameter. Therefore, as No. 10 is 0.10 inch.
No. 16 is 0.05 inch, and No. 30 is 0.01 inch; also No. 4 is
0.20 inch, and No. 000 is 0.40 inch; also No. 0 (two sizes
smaller than No. 000) has 80 per cent, less diameter, or 0.32
inch. No. 00, Ijring between these sizes, may be presumed to
be about 10 per cent, less than No. 000, or .36 inch; the diam-'
eter given in the wire table is 0.3648.

Reference to a complete wire table will show that the fig-
ures in the above examples, and other figures which may be
determined in the same way, are correct within a few per
cent. A little practice in mental arithmetic will enable coiy-
one to determine the approximate weight and resistance of
wire of any size.

Summary. The things to be remembered regarding B. &
S. gage copper wire are as follows:

A wire which is three sizes larger than another wire has
half the resistance, twice the weight and twice the area. A
wire which is ten sizes larger than another wire has one-tenth
the resistance, ten times the weight and ten times the area.

No. 10 wire is 0.10 inch in diameter (more precisely 0.102);
it has an area of 10,000 circular mils (more precisely 10,380);
it has a resistance of 1 ohm per thousand feet at 20 d^rees
Centigrade, (60 '^ Fahrenheit), and weighs 32 p>ounds (more
precisely 3 1 .4 lbs.) per thousand feet.

The weight of 1 ,000 feet of No. 5 wire is 100 pounds.

The relative values of resistance (for decreasing sizes) and
of weight and area (for increasing sizes) for consecutive sizes
are:

.50, .63, .80, 1.00, 1.25, 1.60. 2.00

524 ALTERNATING CURRENT SIGNALING.

The relative values of the diameters of alternate sizes of
wire are:

.50. .63. .80. 1.00. 1.25, 1.60. 2.00

Circular Mils. Conductors of large size are usually speci-
fied in. circular mils. For example, 500,000 circular mils.
750,000 circular mils.

As No. 1 0 wire has approximately 1 0,000 circular mils and
a resistance of 1 ohm per thousand feet and as a length of wire
which has a given resistance is proprotional to its area, it
follows, therefore, that the length in feet of a copper conduc-
tor having a resistance of 1 ohm may be found by dropping
one cipher from the number expressing its circular mils; for
example. No. 10 wire has 10,000 circular mils and a resistance
of I ohm per thousand feet; a 300,000 circular mil conductor
has a resistance of 1 ohm per 30,000 feet, and a 1 .000,000 cir-
cular mil conductor has a resistance of 1 ohm per 100,000
feet. The weight of a given length is proportional to its area;
therefore, the weight of a conductor having 500,000 circular
mils is greater than that of No. 1 0 wire in the same ratio that
its area is greater. Five hundred thousand circular mils is
fifty times that of No. 10 wire, or approximately fifty times
32 pounds, which equals 1 ,600 p>ounds per thousand feet. In
this way, the approximate characteristics of copper conduc-
tors of all sizes may be quickly ascertained.

To find resistance, drop one cipher from the number of cir-
cular mils; the result is the number of feet per ohm.

To find weight, drop four ciphers from the number of cir«
tfular mils and multiply by the weight of No. 1 0 wire.

TABLES AND DATA 525

WRITTEN CIRCUITS

'While much is being done toward standardization of railway
signaling matters in general, little has yet been done toward
standardizing signal nomenclature. Referring especially to
the field of electrical signaling, all recognize the necessity for
not only suitable nomenclature, but also abbreviations of
same. In other words, we must have commonly accepted
names for devices used for various purposes, and suitably sug-
gestive abbreviations for use in place of them. In preparing
circuit plans of small proportions, we can write out the com-
plete name of an operated unit or wire, but with large plans
this is not practical, and abbreviations are thus highly desir-
able, if not entirely necessary. This necessity having been
genereJly recognized, various railroads, as well as signal com-
panies, have been independently devising codes of abbrevia-
tions for naming units and wires. These independent efforts
have naturally resulted in several more or less different codes.
It is cmly natural that the signal companies p>ossibly more
than the railroads should feel the necessity for concerted .ac-
tion along this line. They, therefore, have undertaken to
evolve a code of signal nomenclature and abbreviations which
would, as near as possible, combine all of the good sugges-
tions involved in the various independent systems extant.

The Manufacturers' Committee at the outset considered
that the first move should be to evolve a system of abbrevia-
tions to cover electrically operated units, and recognized that
the system must be somewhat elastic, in order to cover the
multitude of conditions involved. They saw that this system
must be. in a sense, a language, and while they might lay down
certain rules for using this language, they realized that much
liberty must be allowed in order to make the system sufficient-
ly flexible to cover varied conditions. It is expected, there-
fore, that within certain limits, one person may name a unit
differendy than another. This variation will be due largely
to two persons placing different relative importance upon the
various functions of the unit. However, if the system is fol-
lowed consistendy, the meaning can not be mistaken. For
instance a relay which controls the home or 45 ° function of a
a signal may be named by one engineer "HR," meaning
"Home or 45 ^ control relay." Another may choose to name

526 ALTERNATING CURRENT SIGNALING.

it merely **hV*, which has exactly the samejineaning. If the
signal chances to be one governing east-bound movements
another may desire to use "EJ-I", meaning "Eastbound hoine
or 45 ° control relay/* Still another, if the relay should have
an indicating attachment (indicator), may desire to empha-
size this characteristic and use *'KH"» meaning "Indicating
home or 45 ° control relay."

Having named the devices, we turn to the naming of the
wires which control them, and as the two are always associated
it seems most natural to use the same name, except to add a
suffix number to differentiate the positions in the circuit.

While nomenclature, as described above, applies to circuits
drawn up in any form, the discussion thus far leads us very
naturally to the subject of "Written Circuits.*' The old
method of drawing up signal circuit plans starts with the track
plan, more or less to scale, and shows the symbols for the vari-
ous pieces of apparatus. These symbols, in a general way,
are placed in their proper relative positions, after which lines
are drawn representing wires connecting those points which
should be electrically connected. This method is quite ade-
quate for small installations, but it is entirely insufficient for
many of the installations of large proportions with which sig-
nal engineers are having to contend more and more. The
plans are likely to become prohibitive in size and the wires, aa
indicated by the lines, take such indirect courses that they are
extremely difficult to follow. On account of these difficul-
ties, some little thought has been given, during the last few
years, to the matter of simplified circuits, which have been
termed "Written circuits." In written circuits litde or no at-
tempt is made to show the units in their proper relative posi-
tions and,' instead, much emphasis is placed upon the impor-
tance of arranging circuits in straight lines, as far as possible,
so as to render them easy to follow. This necessitates a com-
plete nomenclature of the units for ready reference. The
Manufacturers' Committee, therefore, considered it quite op-
p>ortune to propose, at this time, a standard scheme for writ-
ten circuits as a logical sequence to the subject of nomencla-
ture.

^ All this work on the part of the Manufacturers* Commit-
tee is, in a sense, a continuation of their work on Standard
Symbob, which was completed in 1911, and is respectfully

TABLES AND DATA. iSff

submitted to those interested in railway signaliotg with the re-
quest that the same hearty co-operation may be enjoyed as in
the case of Standard Symbols.

NOMENCLATURE OF ELECTRICALLY
OPERATED UNITS

The term Electrically Operated Unit is used to signify a sig-
naling device in which a magnetic coil in some form is usu€dLy
essential to its operation; as for instance a relay, signal oper-
ating mechanism, electric lock, indicator, etc.

In order to provide a concise, suggestive graphic code for
marking these units on plans, the following system has been
evolved, which makes use of a designation made up of two
parts, namely:

1st. Numerical Prefix. The number of the principal levei;,
signal, track circuit, etc., entering into the control of or con-
trolled by the unit.

2nd. Alphabetic Term. Consisting of one or two let-
ters. The first letter, when used, describes specifically the
operated unit. The second letter designates the general kind
of unit.

The complete designation of a imit is written as follows:
(Numerical Prefix) (First Letter) (Second Letter)

As 10 H R

Written 1 OHR (without dots or dashes).

In this example the number "10** is the number of a signal.
'*10R** means relay having to do with signal 10 and *'10HR"
meeins home or 45° relay for signal 10. In other words the
letter "R" means relay in general and corresponds with a noun
in ordinary language. The letter *'H" indicates that the
/unction of this re!ay is to control a home signal and corres-
ponds with an adjective in ordinary language. And the nuxn-
ber "10" definitely indicates the signal which this home reU^
controls*

528

ALTERNATING CURRENT SIGNALING.

TABLE OF MEANINGS OF LETTERS
(As applied to operated units)

First Letter {^^«^«^'^

B
C
D

P
G

H
J
K
L

— Approach or axmimciat-

ing.
— Block.

— Distant or 90®.

— Ilast or Eastbound — East

bound route locking.
— Traffic.
-^Signal.

— Home or 45®.

— Indicating (visually).
— Locking — Left.

N — Normal — North or North
bound — North bound
route locking.
-Repeating.

P
Q

T
U
V
W

X
Y

— Reverse-

-South or
South
locking

-Track circuit.

-Right — Red.
South bound —
bound route

-Train stop.

-Switch — West or West

boimd — West bound

route locking. '
-Bell.
-Slotting.
-Special (to be explained

on plan).

Second Letter \ deslgnative or
i noun term

A — ^Annunciator.

B
C
D

F
G

H
J
K
L

M —

-Distant or 90® relay.
-Electric light.

-Signal operating mechan-
ism.
-Home or 46® relay.

-Indicator (visual).

-Lock preventing initial
movement of a lever
from normal or re-
verse positions.

■Lock preventing final or
indication movement
of a lever.

N —

P — Repeater.

Q — Local coil (Double ele-
ment relay).
R —Relay.
S — Stick relay.

T — Telephone.
U —

V — Train stop. .

W — Switch operating mech-
anism.

X —Bell.

Y —Slot

Z — Special unit (to be ex-
plained on plan).

Note: — In case of three-position levers, where it is necessary to
distinguish between right and left positions, use R (right) or L
(left) before the lever number; as RIO, LIO.

Also when one lever controls two or more signals use letters A,
B, C, etc., as prefixes to lever numbers; as A 10, BIO, CIO, etc.

In case of three-position levers controlling two or more signals
in each position use combinations as follows: RAIO, RBIO, LAID,
etc.

TRACK CIRCUIT NUMBERING

A track circuit is designated by the letter "T" preceded by
a number.

\ Track circuits within interlocking limits are numbered from

TABLES AND DATA. 529

•witches lying within them, which are chosen in the following
order:

Take number of an M. P. Frog or in its absence
Take number of a Switch or in its absence
Take number of a Derail.
When there are no interlocked switches in a track circuit,
it is nimibered from a signal governing over the track circuit.
Example:

10T meaning track circuit in which switch 10 is located
or track circuit in block of signal 10 which does not. con-
tain an interlocked switch.
In case of a plurality of track sections which by the above
rules would have like designations, they will be distinguished
by progressive alphabetical prefixes, as:
10T, A10T, B10T, C10T, etc.
Track circuits, in which there are no interlocked switches,
and which do not govern signals (as track circuits controlling
annunciators only), are given arbitrary numbers 01T, 02T»
etc. In many cases these arbitrary numbers 1, 2, etc., may
indicate the track numbers.

EXAMPLES OF COMMON COMBINATIONS

Note: — ^When the second or designative letter alone de-
scribes the characteristics of the unit sufficiently, the first or
descriptive letter may be omitted; that is to say the noun may
be used without the adjective. For instance, if there is but
one euinunciator on a track the letter A (meaning "annuncia-
tor") is sufficient. If there are two annunciators on a track,
one operated by track section or sections in the rear of the
distant signal and one operated by track between home and
distant signals, these will be named DA and HA respectively.

The designation of an operated unit numbered from a track
circuit is made up of the number of the track circuit followed
by the letter "T" and the proper second letter; as 1 0TK, 1 0TP,
10TR.
10A — ^Annunciator indicating approach to signal 10. (First

letter not required).
10HA — ^Annunciator indicating approach to home signal 10.
lODA — ^Annunciator indicating approach to distant signal

SdO ALTERNATING CURRENT SiCNALING.

U)£A — ^Eastbound annunciator indicating approach to sig-
nal 10.

1 0D — Relay ccm trolling distant or 90 ° position of signal 1 0.

i OKD — Distant or 90 ° relay for signal 1 0 with indicating at-
tachment.

iiODG — Distant or 90 ° signal operating mechanism of signal
10.

10HG — ^Home or 45° signal operating mechanism of signal
10.

I ORG — Stop indication device of signal 10 (as with light sig-
nals).

I OH — Relay controlling home or 45 ° position of signal 10.

JOKH — ^Home or 45° relay for signal 10 with indicating at-
tachment.

10BK — Indicator controlled by track circuits in block of sig-
nal 10.

1 0FTC — ^Traffic indicator for traffic lever 1 0 or for track num-
ber 10.

10NK — Indicator indicating normal position of unit 10.

YORK — Indicator indicating reverse position of unit 1 0.

10TK — Indicator indicating condition of track circuit 10T.

10WK — Switch indicator in block of signal 10 or indicator in-
dicating position of switch 10.

MXL — Lock locking lever 10 in full normal or full neverse
positions or both.

lONL — Lock locking lever 10 in full normal position.

10RL — ^Lock locking lever 10 in full reverse position.

10FL — ^Traffic lock locking lever 10.

IQM — ^Lock preventing lever 1 0 from making its final or in-
dication stroke.

fONM — Lock preventing lever 10 from making normal indi-
cation stroke.

liQRM — Lock preventing lever 10 from making reverse indi-
cation stroke.

I-O^' — ^Relay or indicator repeating track circuits in block
of signal 1 0.

lOGP — Relay or indicator repeating signal 1 0.

1 OHP — Relay or indicator repeating home or 45 ° position of
signal 10.

tf^^ — ^Relay or indicator rq^ieating distant or 90*
of signal 10.

TABLES AND DATA. 531

IOTP — Relay or indicator repeating- track relay lOTR.

I ONP — Relay or indicator repea ting normal position of unit 1 0.

1 0RP — Relay or indicator repeating reverse position of unit 1 0.

10WP — Relay or indicator repeating position of switch 10.

1 0Q —Local coil of relay I OR.

1 0TQ —Local coil of track relay 1 0TR.

1 0HQ — Local coil of home or 43 ° relay controlling signal 1 0.

lOAR — Relay controlled by approach section for signal 10.

lOHR — Relay controlling home or 43 ^ position of signal 10.

1 0DR — Relay con trolling distant or 90 ° position of signal 1 0

10TR -^Track relay for track circuit 10T.

1 OS — ^Stick relay used in connection with unit 1 0 or track

circuit lOT.
1 0AS — ^Approach stick relay used with unit 1 0.
1 0LS — Stick relay for locking used with unit 1 0.
lOElS — ^Stick relay for eastbound route locking used with

unit 10.

Note: — Use N, S and W likewise.
I OT — ^Telephone 1 0 (arbitrary number).
1 0RW — Reverse switch operating mechanism of switch 1 0.
1 0NW — Normal switch operating mechanism of switch 1 0.
10X — Bell 10 (arbitrary number).
1 0DY —Distant or 90 ° hold-arm or slot of signal 1 0.
1 0HY — Home or 45 ° hold-arm or slot of signal 10.

The above list, while not presumed to be exhaustive, covers
many of the most common combinations. Others may be
made up as required.

WIRE NOMENCLATURE

A wire carrying positive energy to one or more operated
units is in general designated by the name of the principal
operated unit controlled by it, followed by a number indicating
the number of circuit controlling contacts in the circuit be-
tween the wire and the unit.

A wire carrying negative energy to one or more operated
units is designated in the same manner except that the desig-
nation is preceded by the letter "N," However, this letter
may be omitted if desired.

Example:

532

ALTERNATING CURRENT SIGNALING.

In case of branch wiring the above method is applied to
the principal circuit. The letter "A" is appended to distin-
guish the first branch, the letter "B" distinguishes the second,
etc.

Examples:

fOff

fOit/ fOW

/0K2

/OKt ^ ^/0ft2A tfif^A tMJA

"^^

fOif

/OR

/OR/

/OR/ . /OR/

/OR/

•• »

/OR/

/0R2
/OR2A
JOR2£_^

10 H /OHI

I0H2 ^ ^ /0H3 /0//3 ~r^/a//4 {■

•3
'3

'3
'3
'3

Two or more wires leading from the same bremching point
or group of connected branching points bear the same wire
designation as shown in the preceding escamples. In the in-
stallation such wires are frequendy not connected together in
the same order or with the same arrangement of terminals as
that conventionally shown on the circuit plans. In such cases
the designation of the device or terminal location to which
each wire leads, may be added to the wire designation on the
tag (under the wire designation or on the back of the tag as
may be most convenient). In this case a group of terminals,
which are connected together by wires having the same wire
designation, are distinguished by the let^rs "A," "B," *'C,"
etc., when necessary. In the following examples the tags are
indicated by rectangles attached to the lines representing the
wires.

TABLES AND DATA.

533

N-

SW/TCH

refiff/HAL

LOCATION
A

_S/SJtT

^ 8P

reHMlNAL OAf

LOCATiON SW/TCH.

3 NaT

Tein

7¥lf

\ioiti

l^-

fW s_

TSR^/MAL

Other wire designations are as follows :
C — Common Wire, or in combination when necessary as

follows:
CH
CL
CIO
C20
CX

meaning 1 1 0 volt D. C. common,
meaning low voltage D. C. common,
meaning common for 1 0 volt D. C. system,
meaning common for 20 volt D. C. system,
meaning A. C. common.

CX55 meaning A. C. 55 volt common.

B — Positive Elnergy or in combinations where necessary as
follows:

BH meaning 1 1 0 volt D. C. positive.

BL meaning low voltage D. C. positive.

BIO meaning positive of 10 volt D. C. energy.

B20 meaning positive of 20 volt D. C. energy.

BX meaning A. C. positive energy.

BX55 meaning A. C. 55 volt positive evergy.

N — Negative Energy or in combinations when necessary as
follows:

NH meaning 1 1 0 volt D. C. negative.

NL meaning low voltage D. C. negative.

NIO meaning negative of 10 volt D. C. energy.

N20 meaning negative of 20 volt D. C. energy.

NX meaning A. C. negative energy.

NX55 meaning A. C. 55 volt negative energy.

S^ ALTERNATING CURRENT SIGNALING.

EB — Poative lif^ting wire (not a Light Signal wire).

EN — ^Negative lighting wire (not a Light Signal wire).

TB — ^Positive track feed wire with number of track circuit

precedihg, as 10TB.
TN — ^Negative track feed wire with number of track circuit

preceding, as lOHTN.
RB— Poflitive track relay wire with number of track circuit

pf^Bcedingt as lORB.
RN^-Negative track relay wire with number of track circuit

preceding, as lORN.

SYMBOLS FOR OPERATED UNITS.

An operated unit is represented by a rectangle with the nu-
merical and alphabetical designations indicated therein, as:

RELAY AND INDICATOR CONTACTS.

Front contact of 2-position relay closed. , yyw

Front contact of 2-position relay open. i ^S^"*

Back contact of 2-position relay closed. < ^f^^x

Back contact of 2-position relay open. j a

Polar and 3-position relay contact, closed

when normal. fotp

Polar and 3-position relay contact, closed ^ayAc

when reversed. '>fSMt

Polar and 3-position relay contact, closed J^

when de-energized.

Note: — Fig. "3" above indicates third contact of relay count-
ing from left to right.
With 2 position relay contacts:

C means battery flows from heel to point.
C means battery flows from point to heel.

Indicate direction of current through pplar ^jeA ^ i

S-position contacts by arrow point, thus ^

TABLES AND DATA.

CIRCUIT CONTROLLERS OPERATED BY i£VERS.

Use R. S. A. symbols as shown on .p«9e 5,1>2 as follows:

iJVK.

CIRCUIT CONTROLLERS OPERATED BY SIGNALS.

Qosed at 0** only.
Closed at 45 ** only.
Closed at 90*" only.
aosedat60*'oidy.
Closed between 0^ and 45^.
Closed between 45 "^ and 90*".

90
JO

CIRCUIT CONTROLLERS OPERATED BY SWITCH

POINTS.

Closed wben switch is nonnal.
Closed when switch is reversed.

^smnz^m^mM'

CIRCUIT CONTROLLERS OPERATED BY LOCKING
MECHANISM OF SWITCH MOVEMENT.

Closed.
Open.

TIME RELEASE CONTACTS.

Normally closed.
Normally open.

Note: — 10 indicates number of signal whoee route is re-
leased.

LATCH CONTACTS.

Normally closed.

ik^

Nofmally open. ■ fr^^

536

ALTERNATING CURRENT SIGNALING.

PUSH BUTTON AND STRAP KEYS.

Normally closed.
Normally open.

^ •

j<z.

■ •

FLOOR PUSH.

Normally closed.
Normally open.

£l

TRAIN STOP CONTACT.

Closed.
Open.

Following is an example' of a written circuit plan:

-I— •

^tf4i'

TSTT

-•— r

TS3Jr

-**■

-rr*-

^=^

^fiij*

r
I
I
I

TOW€R

i.,fr^

/fjuj

J u^/y/^/ w^iyr/*

//«

jao.

v^y

j/y

"^319

/^j

,^ ,/#/ ,y , /If/

Uoi\ IDG JP V

-B
-3

m/ pyi

^lA^ m Iff nxn

m 37H. IM

IMI

A^^ —
^\ IM

J,dK

rf3ii (Y3i

fin

•c
-c

'C
'3

INDEX

Accessories 417

(See also under name of device)
Adjustable filler transformers. . 194, 214

Advantages of A. C. signaling 23

Aerial transmissions 336

(See also .Transmission Sys-
tems)
Air cooled tmnsformers. . . 193, 197-203

(See Transformers)
Air gap

in impedance bonds 152, 161

induction motors 248

induction slots 259

track impedances 226

transformers 2 16

A. C. propulsion roads, apparatus

for 158

Alternating Currants 29

amplitude factor of 56

books on 62

calculations

general 29-62

trac.k circuit 437

circuits

phase relations in 43

power in 58

power factor of 58

reactive factor of ^ . . . 320

definitions 39

(See also under desired term)

generators

simple 31

multipolar 40

turbo 41

interlocking 365

(See also Interlocking)

measurement of 42

meters 431-435

ammeters 433

frequency. . . ; 345

phase 435

synchroscope 345

voltmeters 431

relays 79

(See also Relays)

signaling

histcrrical sketch 7

advantages of 23

signals 239

(See also signals)

theory of 29

transmission systems 303

(See also Transmissions) .

vector diagrams

principles and use 43

track circuit 446, 454

Alternation, definition of 39

Alternators 3.1

multipolar 40

Altematon — C<mt.

simple 4i

turbo 41

Aluminum

electrolytic lightning arrester. . . 347
wire
comi)ared with copper. . . .336, 337

cost of 337

reactance, tables of SIS, 316

resistance, tables of

solid 471

stranded 336

Ammeters 433

American wire gauge 461. 464

Amplitude factor 56

Angles

measurement in radisois 38

cosine, definition of 37

sine, definition of 37

tangent, definition of 37

Apparent power in A. C. cucuits. . 58

Approach locking 405

Arresters, lightning

(See Lightning Arresters)
Atchison, Topeka & Santa Fe

steam road A. C. signaling on.. . 21
Average values of currents and
voltages, definitions of 42

Backgrounds for light signals 286

Ballast

conductance : 442

kinds and resistance of 442

leakage, effect of 66

resistance 442

Beam light signals 297

(See also Signals. Position)

Bonding of track circuits

kinds %6

resistance of bond wires 441

Bonds, cross 156

Bonds, impedance 150-157, 160-170

air gap in 152, 1^1

capacities, standard 162-166

construction of 154

description of 150

filling compound 154

for A. C. propulsion roads 160

for D. C. propulsion roads.. 154, 155

invention of 16

layouts for 167-170

power factor of 452

theory of 150

unbalancing in 152

effect of 1512

permissible amount 45^

proviaion agninit 1^

540

ALTERNATING CURRENT SIGNALING.

Books on alternating currents 62

Boston Elevated track circuit

description of 10-12

limitations of 12

relay for 10

British standard wire gage 462

resistance of copper wire per. . . 470

Brown & Sharp gage. 461

. resistance of copper wire per . . . 468
for sheet copper and brass 467

c ■ •

Cables, stranded copper, table of. . 469
Cement, mixing and proportions. 517
Calculations, altanating current

general.. ,.,..-...• 31-62

track circuit. ...... .-. 437

transmission line 303

<2apacity

. in A. C. circuits, efifec^ of i 53

' of impedance b6nds 162-166

track impedances 225-232

track resistances 236

^ transformers ,. . 197-217

: unbalancing of impedance bonds 153

Centigrade to Fahrenheit : 502

Centre fed track circuits / . . 66

Centrifugal rtlay 129

(See alsor under Relays)

Check locking. 410

Chicago, MUwaukee & St. Paul
. steam road A. C signaling on.. . 21

Churchill, Dr. William. ,., 297

Circuits

alternating current

phase relations in 43

power factor of..-. 58

power in 58

for signals

Style " B'* 269, 270

"S*! 274

"T-2" 281

. interurban signaling 356

'. symbols for (R. S. A.) 504-515

type "F" system 365

written < . . . . 525

Circuit controllers
switch circuit, Type "F"... 388,391

universal switch circuit 422

Clockwork time release 429

Color Ught Signals 286

(See also Signals)

Commutator motors 253

(See also Motors)

Comparison of wire gages 464

Compression chamber lightning ar-

'rester 341

Concentrated ballast leak method.

limitation of 446

< theory of 443

Condenser

description of 53

. effect of in A. C. circuits 53

Conductance, ballast 441

Controllers
universal switch circuit 442

Copper.

bond wires, use of 76, 441

losses in transformers 184

sheet, weight of 467

wire, tables for

carrying capacity 475

enameled 462

hard drawn line.

strength 474

resistance and weight c^. . . 336
soft drawn
solid

resistance and weight. . . . 468
stranded

resistance and weight. . . , 469
Copper clad

bond wires, use of 76, 441

wire, resistance and weight of.. . 473

impedance of 317

Core losses in transformers 182

type transformer 189

Cosine, definition of 37

tables of 482-485

Cross bonding on electric roads. . . 156

protection. Type "F" system. . . 397

Cross-overs, table of 496

Currents, alternating

(See also Alternating Current)

average value of . . . ; 42

effective value of 43

instantaneous value of 43

lagging 44

leading 44

maximum value of 43

root mean square value oi 43

theory 31-62

unbalancing 152

Cut-outs, primary fuse 339

Cycle, definition of 39

D. C. propulsion road

apparatus 76, 141

(See also Track Circuits and
Bonds)

Decimal equivalents, table of 491

Decimal gage for sheet iron and

steel 466

Definitions; see under term

Delta connections, three phase.... 33C

Detector Track CircuiU... 396.399

Detector relay 390, 391

Distributed core type transformer. 190

Distributed leak method 442-454

compared with centre leak

method 446

description of 442

formulae for 444

vector diagrams for 446-454

Double element relays. 68

(See also Relays)

Double rail track circuit 77, 150

(See under Track Circuits)

Eddy . currents 105

losses in transformers 182,483

INDEX.

54 W

Effective values of currents and

voltages, definition of 43

Efficiency

of transformers 187

of transmission systems 305-307

Electric locks. 424

Electric road signaling; see also
undersubject or name of device

141, 349

Electrolytic lightning arrester.. . . ., 347

Elements of a. c. signal system 65

of a. c. track circuit 65

Enameled copper wire, table of 463

Estey, Wm., on Alternating Cur-
rents 62

Exciters for alternators 40

Fahrenheit to Centrigade 502

FoUett, W. F.. : 367

Fleming's right hand rule 35

Foundations for Signals

style "B" 272

style "S" 276

style "T-2" 285

Frequency

definition of 39

meter 345

relays 78, 129-140

(See also Relays)
Fuse cut-outs, primary 339

Gages

classification 461, 464

sheet metal. 465-467

twist drill 486

wire

Brown & Sharp 468

British standard 470

Generation of alternating currents.. 3 1
German Silver wire, table of re-
sistance and weight 479

Galvanized irdn and steel wire
resistance, strength and weight

^ of 472

Galvanometer Relays 93, 105

(See also Relays)
Graded shunt lightning arrester. . . 342
Ground shield 191

Hay, Alfred, on Alternating Cur-
rents 62

Henry, definition of 50

History of a. c. signaling 5

Holding clear devices 257

induction slots 259

tractive type slots 257

shaded pole slots 257

Hoods for light signals 286

Howard, L. F 19

Hudson & Manhattan R. R.
track circuits on 18

Hyperbolic functions, 444

Hsrsteresis Losses

cause of ig^

in transformers 182" 183

Illinois Traction System

interurban signaling on.. ... ' 2I
Indication circuits. Type "F" Sys-

Indl«to»- ...389-396

Switch, Z type 410

Tower.Ztype ;::;; 420

Inductance
bonds, see Bonds
definition of jq

effect of in a. c. circuits. '. \ '. '. ' 48. 58
Impedance
bonds, see Bonds

definition of 43

effect of in a. c. circuits*. '.'.'..' 48 58

for track circuits 75, 219

description of. ■....' 222

use of ['[' 222-224

of copper clad wire ! ' 317

of rails "**'

effect of ; 439

table of !!.*"** 440

Induction

motors > 241

(See also Motors, indue-'
tion)

slots 2 so

(See also Slots)' ' *

Instantaneous values of currents
and voltages, definition of. .... 42

Instruments, measuring 431

ammeters * 433

phase meter ......* 434

volt meters ......' 431

Insulated Joints Keystone. . 425, 426
Insulation of transformers. . 191

Interboro Rapid Transit

description of signaling on 14

efficiency record of * ' 15

Interlocking, a. c . ?6S

, (See also^ype "F" System)' ' '
Interurban Road Signaling.... 349

circuits for 355

double track signaling.. ..,..." 351

examples of " ' " 359

general layout for ." .' '353, 354

impedance bonds for 155, 154

power house equipment for 358

switchboards 346, 359

relays for 355

signals for 358

single track !....! 351

T. D. B. system ,.. 351

Iron

bond wires, use of 76, 441

wire, resistance and weight of.. , 472
losses

cause of i82

in transformers ......... 182 ,183

542

ALTERNATING CURRENT SIGNALING.

Iflkckson, D. C. and W. B., on Al-
. temating Currents 62

Karapetoff , V., on the Electric Cir-
cuit 62

on the Magnetic Circuit 62

Keystone insulated rail joints. . . . 425-6

Lag* definition of 44

screws, table of sizes. 494

layouts for impedance
bonds 155, 167-170

hesidt definition of 44

Leakage
ballast

effect of 66, 441

usual values of 442

magnetic

in induction motors. 248

in transformers 180, 194

Lewis, L. V 443

Line, transformers 74, 205

(See also Transformers)

L^sht Signals 286

(See also Signals)

Lichtning Arresters

aluminum cell 347

compression chamber 341

electrolytic, aluminum 347

graded shunt 342

spacing of in transmissions 341

spark gap 428

Local element of relays, function
of 68, 69

Locking

approach 405

between towers 410

. check 410

mechanical 376

route 403

Locks, electric 424

Logarithms

theory of 498

tables of 500, 501

Long Island R. R.
double rail track circuits on 18

Losses in
transformers

copper 184

eddy current 183

hysteresis 182

iron 182

transmission systems 307

Machine. Type F interlocking 370

Magnetic

field, influence of in a. c. circuits 48, 49
leakage

in induction motors 248

in transformers 180, 194

•'agnet wire, tables of 476-478

Magnetizing current 1 76

Maximum values of alternating

currents and voltages 42

Measuring instruments

ammeters 433

phase meter 434

volt meters 431

Measurement of alternating cur-
rents

average values 42

effective values 43

instantaneous values 42

maximum values 42

root mean square 43

Meters; (see under Measuring In-
struments)
Metric system
compared with English system. . 490

Model 12 electric lock 424

Model 12 lightsignal 288

Model 13 light signal 290

Model 14 light signal 293

Model 12 polyphase relay Ill

Motors

signal 241-259

commutator type

description of 253

theory of 253

induction type

characteristics of 241-253

description of 241

magnetic leakage in.. ." 248

rotor of 241

rotating field in 242, 243

single phase 248

slip in 246

speed characteristics of 246

split phase 248

starting 247

theory of 242

three-phase 251

torque of 246

two-phase 242, 251

switch

compensated series type

description of 384

theory of 384, 387

Multipolar alternators 40

Nails, common wire, size and
weight of 494

New York, New Haven & Hart-
ford
frequency relays on 19

New York Subway

description of signaling on 14

efficiency record of 16

track circuit system on IS

New York, Westchester & Boston
R. R.
track circuits on 20

Norfolk & Western

frequency relays on 20

steam road a. c. installations on 21

North Shore R. R. track circuits
on 13

INDEX.

Ohm's Law, applied to a. c. cir-
cuits 48

Oil cooled transformers; see
Transformers 193, 205

Open magnetic circuit transform-
ers 216

(See also Transformers)

Pender, H., on Electrical Engineer-
ing 62

Pennsylvania R. R.

double rail track circuits on 18

frequency relays on 20

New York Terminal 18

steam road a. c. signaling on. . . 21

Performance of transformers 186

Period, definition of 39

Petrolatum, use of in bonds 154

Phase

definition and meaning of 43

meter. 434

relations in a. c. circuits 43

in a. c. track circuits.. 75, 221

transformation 334

Scott or " T " connection 334

Philadelphia Rapid Transit.

track circuits on 16

Pipe, standard wrot iron

sizes and weights, table of 481

Polarized indication " SS " relay. ... 394
Poles

spacing of in transmissions 337

signal, length of

Style "B" 272

"S" 276

"T-2" 285

Polyphase

motors; see Motors
relays; see Relays
transmissions; see Transmis-
sions

Position light signals 297

(See also Signals-position)
Power
calculations

track circuit 437

transmissions 303

(See also Transmissions)

factor 58

factor triangle 458

in a. c. circuits 58-62

apparent 58

true or real 58

watts 58

volt amperes 58

for relays

iron galvanometer 108

ironless galvanometer 99

polyphase model 12 120

polyphase radial type 126

vane, single element 88

for signals

8tyle"B" 271

Power — Continued.

"S" 275

••T-2" 284

for track circuits

(See under relays aboveX
Power house equipment

elements of 344, 358

switchboards for 344, 359

Primary fuse cut-outs 339

Properties of a. c. circuits. 48. 58

Quadrature

definition of 53

relationship in polyphase

relays 75, 114

Rail

bonding 76, 441

contact resistance with wheels. . , 455

impedance, table of 440

joints. Keystone insulated 426

sections, table of 497

skin effect in 439

Radian, definition of 38

Rating of transformers 186

Reactance, definition of 52

Reactance factor 320

Reactive transformers 196i 203

Regulation of transformers 185

Reiasrs ^

Boston Elevated 10

d. c. on d. c. electric road 8

detector track circuit 390, 396

double element 68

electric road

d. c. propulsion 76.81,92,111,123

a. c. propulsion 78. 129, 137

frequency

centrifuyai type 128-134

characteristics of 132

power data on 134

vane type 137-140

characteristics of 139

power data on 140

vane type (single element) . . 81-90

characteristics of 86

description of 81

power data on 89. 90

theory of 81

where first used 13

S^alvanometer

ironless type 92. 102

characteristics of 98

description of 93

power data on 99

theory of 93

track circuit calculations for. . 448
use of resistance or impe-
dance with 75. 222. 448

iron type 104-109

characteristics of 108

description of 1*05

power data on 108

theory of 1«5

local element, function of 68» 69

544

ALTERNATING CURRENT SIGNALING.

R«layB — Continued.
polyphase

model 12 111-120

characteristics of 117

description of Ill

power data on 120

theory of 114

radial type 122-127

characteristics of 123

description of 123

power data on 126

theory of 123

indication use of 389

track circuit calculation for 450

use of resistance or impedance

with 223

polarized indication 389

single element principle 68

single element vane 81

selective principle 13, 19, 78

three position

circuits for 70

counterweight system of 97

theory of 70

track element, f uncticm of . . . . 68, 69

two position, use of 70

Resistance, tables oiF
aluminum wire

solid 471

stranded 336

copper wire

soft drawn 468

hard drawn line 336

stranded cable 469

coppca- dad steel wire. 473

galvanized iron wire 472

german silver wire 479

Resistance, ballast leakage

effect of 66, 441

usual values table of 442

Resistances; Track Circuits

function of 75

kinds and sizes 236

on single rail circuits 146, 237

use of with galvanometer

relays 75, 222

polyphase relays . . 75, 223
Root mean square values of cur-
rents and voltages, definition of.. 42

Rotor of induction motor 241

Route locking 403

porcelain terminal block. 516

symbols 504-515

trunking 492^93

Rudd, A. H 23, 297

Sectionalizing switches 339

Scott or " T " connection 334

Selection of track circuit imped-

dances and resistances 75, 222

Selectiveprincipleofa.c. relays.. 13, 19
Self-indu<:tion

definition and unit of 50

Semaphore

signal aspects R. S. A 504, 505

Self-induction — Continued.

signals 241, 285

(See also Signals)
Series commutator motors 253

(See "Motors")

Shell type transformers 189

Sheet metal gages 461-467

Shunting of a. c. track circuits. . . 454
determination of eflFectiveness of

shunt 457

methods of improving 456

Signals

aspects of , R. S. A 504, 505

foundations for 272, 276, 285

lighting of 260

Ucht 286-302

color type 286-295

backgrounds 286

hoods 286

Model 12 288-289

construction 288

lamps for 288

lenses for 288

range of 288

where used 288

Model 13 290-291

construction of 290

- lamps for 291

lenses for 291

range of 290

where used 291

Model 14 292-295

construction .of 293

lamps for 293-294

lenses for 293-294

range of 293

where used 293

Ix>sition or beam : . . . 296-299

aspects, diagram of 299

description of 297

lamps and lenses for 298

Motors, for 241-257

Poles, length of 272, 276, 285

Semaphore 241-285

holding clear devices for 257

(See also slots, below)

lighting for 260

carbon lamps 261

life of lamps 262

number of lamps 262

tungsten lamps 261

motors 241-257

(See also motors)

induction 241-253

commutator 253-257

slots 257-260

induction 259

tractive 257

shaded pole 257

Style "B**^.. . 264-272

circuits for. 26S>-270

description of 265

foundation for 272

holding clear device 267

motors for ft-

induction 267

series commutator 267

tNbfex.

545

SivnaU — Continued .
Style '^B"— Continued.

pole, lengtti oi 272

power for 271

Blot

magnet 267

contact 258, 271

threerpo^ition 267

. twoposition 267

Style **S" 273-276

circuits for 274

description of 273

foundation for 276

holding clear device.. ', 275

• tnoior for 275

pole, length of 276

power for 275

Blot

magnet 275

contact 275

three-position 273

Style "f -2" 278-285

circuits for 281

description of 279

foundation for 285

holding clesir device 280

motor for 280

ijole, length of 285

power for 284

slot 280

Sgnaling

electric roads J4 1

electric interurban road 349

(See Interurban signaling)

. steam road 65

Simple alternator, theory of 31

Sine, definition of 37

tables of 482-485

waves, production of 31

Single element relays 68

(See also Reldys)

Sngle rail track circuits 77, 145

(Sec also Track Circuit)

Sizes of transformers. 197-2 17

Skin effect in rails 441

Slots for Signals 257-260

induction.. 259

tractive type 257

. shaded pole 257

Single phase motors 248-251, 253

. (See also Motors)
SUp

induction motors 246

rings of alternators 32

Southern Pacific

steam road a. c. signaling 21

track circuits in electric zone.. . . 18

Spark gap lightning arrester 428

Split phase motors 248

(See also " Motors, induction")

Stator of induction motor 241

Steam road track circuit appara-
tus 65

(See also under name of device)

track impedance 225

Steel. .

gages for 465-466

ttansformer « 182-3

Steinmetz, C. P., on Alternating

Currents 62

on Electrical Engineering 62

Step-down and step-up transform-
ers 174

Style "B" Signal 264-272

"S" Signal 273-276

•«T-2" Signal 278-285

(See also Si^bai^-aemaphore)
Switchboards
for electric tntemrbsttMWkdft. 346*358

• for steam roads 344

Switch indicator, Z type 418

Switch

circuits. Type "F" 390-391

circuit controllers 388, 422

layouts 398

tnotors.. . . ; 384

Symbols, R.. S. A 504-51 5

Synchronizing 345

Tables; see under subject

Tangent, definition of 37

, lables of 486-489

Taylor, John D ' 19

T. D. B. system 351

. (See also I ntenurb&ft signaling)
Textbooks on alternating cuirents. 62
Thermometers. . . . . ; 502

I centigrade and Fahrenheit . . . 502-3

Three position relays 70

(See also Relays)

THree-phase currents 326

ThuUen, L. H..... 17

Time release, clock work 429

Torque of motors

induction 246

series commutator 253

Tower indicators

Z type ;... 420

vane type. . . •. 421

Track Circuits

boilding bf. 76,441

caleulatibiid 437

centt6 fed 66

detector 396

electric road 141-170

d. c. propulsion rokds

single rail 143-149

characteristics of 148

description of 145

limitations of 148

relays for. 1 47

resistances for 148, 237

transforpiers for 147

double rail ..^ 150-170

centr^fed for interurban

lines. ^ 355

characteristics of 158

cross-bonding on 156

impedance bonds 150

(See also "Bonds")

546

ALTERNATING CURRENT SIGNALING.

Track Circuits — Conthiiied.

Double Rail — ^Continued.

impedances for — ; . 227-232
power calculations fol*^ . > 4^
relays for ..:;*. : 76,: 157, 158

. theory of .' . . . 150

transformers for -,^. 157

unbalancing in. . . i . . . 152

. vector diagrajn- for« . - 45 1

a. c. propulsion roads ^,.V.. 19

double rail - '

impedance bonds for 160, 1 65
;/ (See-also •• Bondsr">

unbalancing oil.. ....... .\ 161

relays frequency for 78* 129, 137
single, rail, on electric road....: 145

elemetits of ;...... . . . . . 63

end fed .- fe5

formulae 442'

impedances for ^ . . 219

pliase relations in 76, 222

I>ower in 437

resistances for.. ............. .^ ... .218-

shunting of ,,,:. .,.,...... ^54

steam road apparatus. .' 65

vector diagrams for. , . 437, 447, 451
Track element of relays, function
of . . 68-69

Train Shunt 454-458

improving effectiveness of. 456

. effectiveness on steam roads 455

effectiveness on electric roads. .. 455
tests on effectiveness of ...... . '. 457

Transformers . 171

adjustable fillet. 194, 214

air cooled track 193, 197-203

electric road 147,157

combined track and line .... 74, 207

commercial sizes of ; . . 205

copper loss in. 1 84

core loss in 182

core type . . . . , 189

cat-ojts, primary fuse. . '. 339

delta connection 330

. distributed core type 190

eificiency of 1 82

elements of 174

fuse cut-outs, primary 339

; >ground shields for 191

indication for Type F system. .. 389

line 204^206

^ commercial sizes of. 205

function of 205

lino and track 207-21 7

sizes of 207-217

function of 74

losses in 182-185

copper 184

eddy current. 183

hysteresis 182

iron. 182

magnetizing current of 1 75

magnetic leakage in 180

nl cooled 193, 205

Transformers — Continued.'

open magnetic circuit. . . . . " 147> 216
performance of 186

^ phase transformation with. . . 334

^ Scott or "T" connection. . . . . 334
power factor, effect 6t. ...,..*,. - 179
primary •. . , ,, .

fuse cut-outs.. . . ^ ..,,., .. .4..' 339

insulation of ^. 191

on no load ,,>..... 1 75

rating of 186

- ratio of transformation of 174

regulation of ....:.. , 185

reactive type 194; 203

Scott or '• T " connection of 334

•Secondary

" ' - insulation of * 191

• V on open circuit 175

'. HftSaiation of . . 185

Shell type 189

Sizes of , . 197-21 7

i commercial line. . . '. 205

combined line and track.. 207-217

track 197-203

Step-up and step-down:;. :- 174

**T" or Scott connected ' 334

theory of 175

three-phase connections. .. > ... .-^ 326

track . ... , 197r-203

tsrpes

adjustable filler . 194, 214

.. air cooled 193, 197-203

'combined line and track.. 207-217

core .189

distributed core. . '. 190

line ... 74,205

oil cooled 193, 205-21 7

reactive 196, 203

- shell 189'

two-phase — three-phase 334'

Transmission Systems 303-348

aerial 336

aluminum wire for

characteristics ..;..-; 337

compared with copper ^ 336-7

table of resistance 336

of reactance 314-316

arresters, lightning ; . . 341/, 347.

(See lightning arresters below)

calculations for 319

copper for

characteristics of .-*..,,... .^ 336-7
compared with aluminum.^' 3il6-7

table of resistance, 336

of reactance 314-:3i6

cost of, factors in 305^3X2

diesiflrn of.

pole spacing * . . . . 337

selection of voltage «. . 308

of line wire size. 306*-312

wire spacing 337

drop in r .-...,. ^ 309

efficiency of 305^312

fuse cut-outs for 159

INDEX.

547

lasmission Systems — Cont.
ightninK arresters for

aluminum electrolytic .347

compression chamber 341

graded shunt 342

ine wire for.
size, calculation of.. . 303-312, 319
(See also copper and aluminum
above)

>ole spacing in 337

»alyphase 325

phase transformation 334

three-phase 326-336

advantages of 332-3

copper economy of 332

description of 326

Scott or "T " connection. . . 334
two-phase-three-phase .... 334
esistance, reactance and imped-
ance 312-317

drop in 317

tectionalizing: 339

:hree-pha8e; see polyphase above

transformations, polyphase 334

mderground 338

iToltage, selection of 308

.vire

aluminum 336-7

calculations for size

of 303-312,318

copper 336-7

spacing . . . •. 337

stringing 337

ue power in a. c. circuits 58

unkina:. Sizes and Capacity

rf 492-3

ngsten lamps 261

[See also signals lighting)

irbo-altemators 41

imouts, table of 495

mt drill gage 480

iro-phase

motors 241-251

transformation to three-phase . . . 334

i^o position relays 70

(See also Relays)

'pe *T" Interlocking 365-416

advantages of 367

check locking in 410

circuits

approach locking 20

check locking 410

indication 390-391

route 403

signal 400

SS signal control 394

switch 390-391

cross protection 397

FoUett, W. F.. inventor of 367

indication, method used

signal 400-3

switch 391

lever movements 373-376

locking

approach 405

between towers 410

check 410

detector 396

Type "F" Interlocking— Cont.

route 403

machine 370

signals

indication circuits 401-2

operating circuits .- . 401-2

types ; 400

"SS control of by switches, . 394
Switch movements. ........ 384-400

circuits for 390-391

controllers for. , . 388-9

layouts for 385-6. 398

mechanism, description of 384

motor... '. 384

time releases in 409

transformer, main

location of 369

size of 368

Unbalancing, in double rail cir-
cuits 152,161

cause of 152

effect of 152-3

permissible amount 153

provision against effect of 153

Underground transmissions 338

(See also Transmissions)

U. S. C^ge for iron and steel plate. 465

Vector

definition of 44

diagrams 43

general 43

of transformer 175-181

principles and use of 43-48

track circuit 446-454

Voltage

average, in a. c. circuits 42

effective 43

instantaneous 42

selection of, for transmission. . . . 308
(See also "Transmissions")
Volt-amperes, definition of 58

Watts, definition of 58

Waves, a. c.

generation of 31

sine 37

West Jersey & Sea Shore R. R.

double rail track circuits on 18

Wire

aluminum 336-7, 471

compared with copper 336-7

resistance of 336-471

solid 471

stranded 336

copper

bonds 76. 44 1

enameled 462

ALTERNATING CUftttfefIT SIGNALING.

Wit«, Copper— CoiitiilUed.

hard drawn line

resistance of $26

strength of 337. 474

weight of 336

magnet 476-478

soft drawn
solid

resistance and T^dght 468

stranded cable
resistance and weight. . . . 469
f ennan silvery table of
resistahiOe and weight 479

Wife, tabled— ColltliluM.

how to remember 521

resistance of wires

aluminilm 336, 471

copper clad steel 473

hard drawp copper 3^6

soft drawn copper 468

Writtfell drcttite 525

XYZ

Yottng and Townsend.

)

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