Railway Electric Traction

RAILWAY

ELECTRIC

TRACTION

BY

F.

W.

CARTER

MA.,M.INSTC.E.,M.I.E.E.,Assoc.AJ.E.E

LONDON

EDWARD ARNOLD

&

CO.

1922

PREFACE

In_{writing this}

book

the authorsethimselfa twofold task:

firstly,to discussihe

methods

ofelectrictraction,as applied

to.Railways; secondly, to

expound

methods

of technical calculation

applicable to the subject. In the pursuance of

thefirstobjectivehe

propounded

to himself,

and endeavoured

to answer, the questions:

What

constitutes

_good

_practice,

and

why

'

Except

where neededforpurposesofillustration,

descriptive matter has been avoided not onlyasbeing

out-side the _scope of the book, but also as being available in full measureinthetechnical press,

and

inthepublications of manufacturers.

The methods

ofcalculation describedin

the _{later_chapters} of the

book

are for the

most

_part the

author's own,

and

do not exceed in refinement

what

he

has_{found necessary}in dealingwith the subject.

The

author wishesto expresshisindebtednesstotheBritish

Thomson-Houston

Co.,Ltd., forpermissionto_{use a quantity}

of data

and

_{diagrams without which}his effort

would have

beenfarless_{satisfying to himself.}

He

also takes this

oppor-tunity ofthanking theInternationalGeneralElectric

Company,

and

theWestinghouseElectric

and

Manufacturing

Company,

for a

number

of views

and

particulars of locomotives, the

J. G. Brill Co. for the _drawing of _fig.15,

and

the Societa

ItalianaWestinghouseforfig. 202.

Itonly remainsto

add

that British units

have

been used throughout the book, the tonrepresenting 2,240Ib.

F.

W.

C.

CONTENTS

PAGE I INTRODUCTORY

...

I II THE LOCOMOTIVE . . . . 21

HE

RAILWAY MOTORS

...

JQJ IV

MOTOB

CONTROL . ₁₆₁

V

DISTRIBUTIONSYSTEM . . ₂₀₃ VI

POWER

EQUIPMENT . . 246

VH

SYSTEMSOP ELECTRIFICATION . ₂₇₈

Vm

PRELIMINARY MECHANICS . . 294

IX

MECHANICS . . _33^

X

POWER

SUPPLY

...

. 355

APPENDIX. TABLEOFLOCOMOTIVESTATISTICS . . 390

INDEX

....

. 408

LIST

OF

FOLDING PLATES

TO3TAO

PAG

MotorBogie, BritishPattern . 3

lotor_{Bogie, M.O.B.Type}

...

.3,

xmgi.tu.dinalSectionofBipolarGearless_{Railway Motor} . 141

.TransverseSectionof Bipolar GearlessRailway Motor 14.

/S. ControlConnectionsofMotor Coach

Hand

Control . 171

80.Control Connections of Motor Coach Relay Automatic

Control . . 171

83. Control Connections of Motor Coach Pneumatic

Cam

Control . . . 17<

88.LocomotiveControl,600volts . . . 18( 89. LocomotiveControl,2,400 volts . 18( 95.Diagram of Connections for Dessau-Bitterfeld Express

Locomotive . . 18f

146. Diagram ofAutomatic Substation Wiring 27*

176. Universal Speed-Distance Curves 35*

<

_CHAPTER

I

INTRODUCTORY

Itischaracteristic of industrial progress to replace

methods

of_{working which}

make

useof _simple tools

and

individual

effort,

by methods which

use costly

and

elaborate _plant

actuated

_by

collectiveeffort. Inthis

manner

labourissaved

atthe expenseof_machinery;

and

the great production

which

ischaracteristic of

modern

industry

becomes

possible. In the

realmof_{transportation,the railway}furnishes

_{an example}

ofa

highly capitalizedbutefficientsubstitute forthe

more

primitive

methodsofearliertimes.

The

useof_{electricity as}themotive

power

of_railways

_may

_{be regarded}as

an

extensionofthe

same

tendency. Itinvolves great outlay for operatingplant;

which

itseeks to justify

by

offering

improved

facilities

and

reduced

runningcosts.

Inthe_workingof railways

by means

of

steam

locomotives,

the driving axles areactuateddirectly

by

the prime movers.

In electrical working, however, there intervenes in general

between prime

movers and

driving axles,thegenerators,the

transmissionlines,the convertingplant, the distributionlines

and

thetrain motors,besidesa_{large quantityof protective}

apparatus

and

controllinggear whosefunctions are ancillary

tothetransmission ofthe power.

When

thewholeof this

plantisthustakeninto account,it isinevitablethat the_capital

invested in motive apparatus should be

much

greater for

electrical_operationthanforsteam operation

The

chief obstacle to the general use ofelectrical_working

beingtheeconomic oneofthe greatinitial_expense,itisnatural

that, inits_inception,itshould have beenlimited tovery busy

linesconcerned withspecialclassesoftraffic. Ithas needed

the developmentofaquarter of acenturytodemonstrateits

technical applicability to allclasses of traffic with

which

a

2

RAILWAY

ELECTRIC

TRACTION

railwayisconcerned; but the economic advantageresultin

from

its_adoptionisBtiH in

most

casesamattertobe determine

by

investigation oftheparticularcircumstances.

Abnormal

Traffic Conditions. Electrical operation he

indeedbeendescribed,not withoutjustification,as

an

expedier forovercoming

abnormal

difficultiesof_working,or forfulfillin

the conditions

imposed

by

special circumstances. For tl

.

ordinary inter-urban railway, in _country of

no

more

tha

ordinarydifficulty, where fuelis plentiful, the question <

electrical_{operation has hardly}

been

considered. Ithashitherl

always been

some

specialconsiderationthathasdetermine

thedecision to electrify.

URBAN

RAILWAYS.

When

_tramway

experience suggeste

theelectrification of

urban

railways,

and

the developmen

effected inpursuitofthis object

were found

to result inmethot

ofworking thetraffic

which

farsurpassed the bestefforts

steam operationin _efficiency

and

economy,electrical oper; tion

was

soon recognizedas

_by

farthe

most

effective

way

overcoming the peculiar difficulties of

urban

and

suburb*

railwayworking.

The

capacityofthelinesisgreatly increase

the operationisfaster,

and

the

working

of terminaltraffic

much

_simplified

_by

electrical operation. This applicati<

indeed

now

_{hardly needs the assurance given}

_{by an}

econon

investigation to justifyit.

TUNNELS.

On

certain railways, the existence of a loi

tunnelhasrestrictedthetraffic

under

steam _operation, t accumulationof_{noxious gases}

from

_{the engineslimiting}t

size

and

_frequencyofthetrains. In a

number

of casesele

trical_{operation has been}

adopted

with aviewto_removingt

restriction.

A

_pioneer

_example

_{of this application}isthat

theBaltimorebelt linetunneloftheBaltimore

&

Ohio Railwa

electrifiedin1895, but the Detroit River tunnelelectrificatic

the

Hoosac

tunnelelectrification,theCascade tunnelelect

fication, the

Simplon

tunnelelectrification,

and

many

oth<

have

beenundertakeninorderto

overcome

the_specialdil

cultiesof_{tunnel working.}

The

New

York

Central

Termu

electrification,

and

indeed thatofall_{lines entering the}oil

was

insisted

_upon

_by

the

competent

authorities, largelyas

result ofa tunnelaccidentattributed toan accumulation

INTEODUCTOBY

3

examplein

which

theobnoxious conditionsoftunnelservice

compelledelectrification.

GRADIENTS.

On

other railways, the gradients

by

their

length

and

steepness

impose

alimit

on

thetraffic

under steam

operation,whichis

removed

orconsiderably ameliorated

by

electrical _operation.

The

electrification of the Norfolk

&

WesternRailroad,a

_heavy

_goodsline,

which

includes a

con-siderablelengthof2 percent, gradient,

was

determined

by

thisconsideration.

The

Chicago

Milwaukee

&

St.Paul

Rail-way, which crossesthe

_{Rocky Mountains and}

a

number

of

other ranges,with

many

long gradients

up

to2_percent,in

steepness,

was

electrified,as tothedivisions affected, largely

forthe

same

reason.

~LA.CS.or FUEL. In

some

regionslocomotivefuelisscarceor

non-existent asalocalproduct, although the naturalresources

of_water-power

_may

be

ample

for_{the purpose}of

working

the

railways electrically,

and

wheretheseconditions exist there

is_{a great}inducementtoelectrify.

The

developmentofelectric

railways in Switzerland, inSweden,inBavaria

and

_{in Italy}is

tobeattributed largely to this state ofaffairs.

The

Chicago

Milwaukee

&

St Paul

Railway

also operates ina region

where

water-powerisplentiful,butwherefuelhastobe brought

from

adistance,

and

this

no

doubt

had

_{large influence}

on

thedecision

to electrify.

The

_history of existing schemes of electrical _operation,

therefore,appearsto_supportthe conclusionthatelectrification

isadevice for special circumstances.

The

inferenceis,

how-ever, hardly justified.

A

more

powerful

and

flexibleagent

having beendiscovered,it isinthe naturalorder of_development thatitshould beappliedfirstwhere

steam

operation has been found wanting,

and

itssuccessunderthesecircumstancesis

notevidence ofits_{inadvisability}under

more normal

conditions.

At

the

same

time,where the requirementsasregards

trans-portation are

met

withoutdifficulty

by steam

operation,the

justification of electrical operation

must

be sought in its

economy

ratherthanin

improvement

intheservice rendered.

Some

increase offaculties isdoubtless to be expected, but

bhere is not scope for the significant

improvement

that

has generally beenfound under the

abnormal

conditions

4

RAILWAY

ELECTRIC

TRACTION

electrical_{operation than with}thenature ofnormalrailway

working.

Improvements

in

Passenger

and

Goods

Traffic

Work

ing. Passengerserviceis_improved

by

running

more

frequen

and

faster trains. Experience indeed has

shown

that ai

enormous

increaseofrevenueresults

from

these causes in th

case of_{railwaysworking}shorthaultrafficinurbandistricts

and

the gainisconsiderablealso_{for railways}which

provid-inter-urban service in well-populated regions.

Long

distant

service,however, doesnot_appeartoofferscopeforthe_improve

ment

possible in short haul service Here,increase ofspeec

is_apttobelimited

by

considerationsofroadbed,curves,etc.

which

have

_nothingtodowiththe_{systemof operation}; an<

the_{reasons for travelling long distances are}notgenerallysue!

as_frequencyof servicewouldaffect.

_Improved

branch-lin

* _services,

_by

_{feeding the}

main

lines

more

efficiently, woul<

,1 doubtlessleadto

some

increase in travel; but onthewhol it_appearsthat,apart from urban

and

certain localizedinter

) urban railways,

no

very great increase in revenue can b

< foreseen astheresultof electrical_operation. Itis,howevei

, largelya questionofpsychology on whichexperience

isno

yetavailable,

and

it is_worthyofremarkthat, inthepast

theincrease ofrevenue_resultingfrom improvedfacilitiesha

usually exceeded allreasonable estimates

Itdoes_{not appear} that goods traffic

would

in generalb

increased

_by

electrification, for no _question of psycholog

comes

into the transportation of _goods;

and

it is onl

occasionallythat asensible

improvement

infacilitiescouldb

offered.

The most

desirableimprovementsinthe_workingc

goodstrafficarenotusually within the

power

oftheRailwa

Company

to effect, andcertainly not suchaselectrificatio

would

influence There are, however, certain incidents

advantagesintheelectrical_operationof_goodstraffic, arisin

primarily

from

thegreatpower on which a locomotive ca

draw. This permitsgreater rapidity in trainworking; an

in_congesteddistrictsallows

more

efficientuse tobe

made

c

thelines.

ECONOMIC

ASPECT. It

_may

beconcluded, therefore, th

apart

from

conditionsof_{specialdifficulty,}

and

fromtraffic<

INTRODUCTORY

5

most part

by

its

_economy

ratherthan

by

the

improved

facilities

itcan offer. In countries_{where water-power} is

abundant

and

locomotivefuelhasto_{be imported, thejustification}isin

generalpresentin_{the saving}offuel,particularlyif

an

industrial

loadcanbe usedto aid in_{the development}of_{the water-powers.}

Where, however,coalisabundant,it is

more

difficultto justify

the electrical_working of normalrailroads. Itis truethat

such workingresultsina_greatsavingoffuel,variously

esti-mated from

ahalfto two-thirds ofthe

consumption

ofthe

steam-workedtrains. Itistrue alsothat asaresultofthe

war, thevalueofcoalis_{likely toremain high}as

compared

withother

commodity

values, sothat the savingisofincreased

significance

But

it is nevertheless _very doubtfulwhether

the saving

would

in generalbesufficientinitselftojustifythe

electrificationoftherailways. In densely populatedcountries,

however, there _{are likely to} be

many

regions of the kind

referredto above, inwhichelectrical_operationisjustified,not

on accountof

economy

ofworking, but

on

account ofthe

increase in revenue,

which

results

from

improved

traffic

facilities.

Where

such conditions exist, the balance

may

readilybe turnedinfavouroftheelectricalworkingofthe

whole railway system; for,with

many

sections oftheline

suitable forelectrical_{operation, the additional}outlayrequired

to

work

traffic, which considered

_by

itself

would

be

un-economical,issmallerthanifthis trafficwereso considered,

whilstthe

economy

of_{the working}isat least as great. Indeed

where

any

considerable section of a locomotive divisionis

electrified for sufficient reasons, it is usually justifiable to

electrifythewholedivision forthesakeof _{the saving}

which

results;

and

ifoneclassoftrafficis

worked

electrically, all

classes_{using the}lines

_may

beso

worked

_{with advantage.}

Technical

View

of Electrical Operation.

From

the standpoint of technical _engineering, electrical _operation is

distinguished essentially as _employing centralized

power

generation, as against the distributed

power

generation of

steamoperation. Thisisatoncea strength

and

aweaknessof

thesystem.

On

theone hand,itenables

_power

tobe

concen-tratedwhereit is

most

needed, thus

making

it_{possible to}

work

heavytrains

on

steep gradientswith economy,

and

to givea

6

EAILWAY

ELECTEIC

TRACTION

engagedinsuburbanservice.

On

theother hand, a

breakdown

atavitalpoint

may

stopalltrafficthroughout

an

extended

area;

and

itisnecessaryto exercisethegreatest care in the

engineering,

and

to

expend

a large

amount

of capital instandby

plant,

and

devices

whose

sole_purposeisthatof_minimizing

the chancesofseriousbreakdown.

Adaptation

of

Methods

to

Agent.

It is a mistaketo

viewelectricaloperationof_{railways simply}asaquestion of

the supersession ofthe steam locomotive

_by

the electrical

locomotive; for the steam-worked railway has grown

_up

around

the

steam

locomotive,

and

thewhole

method

of_working

thetrafficaccordswiththe limitations

and

characteristics of

thismachine. Electricaloperationshould, in likemanner, be conductedtosuitthecharacteristicsoftheelectric_locomotive,

and

indeed ofthewhole_plant. Itis_accordinglyunfair to

electrical_operationto_judgeitaslimited

_by

the methodsof

steam-operation;

and more

orlessonerousto_minglethe

two

methods

of operation.

On

the other hand,confidence

_may

be

feltthat economic estimates based

on

_present methods of

workingwillbe

_{improved upon}

as

more

appropriate

methods

are adopted.

Ingeneral,the great

power

available at

_any

_{point of}

an

electrically

worked

railway,

and

the long continued duty of

whichelectricalapparatusiscapable,

remove

limitationsunder which fltoain _operation suffers;

and

thereby gives greater

freedom

tothetraffic

_managers

in_{dealing with}the

work

of

theirdepartments.

At

the

same

time,ifthe bestresults are

to be obtained, certain limitations of electrical operation

shouldberecognized. Chief

_among

theseis_perhapsthe

desir-ability ofspreading the whole effectiveloadas _uniformlyap

is_practicable,both intimo

and

space,thus

_making

efficienl

useof_{the generating}

and

substationplant,

and

reducingthe

investment therein. Close association is desirable betwcci

goods

and

passenger departments,inorder thattheir respective

load-variations

_may

_{be made,} as far as

_may

bepracticable

complementary

tooneanother.

The

Chicago

Milwaukee

&

St

Paul Railway

takes

power

for

_working

its

_Rocky

Mountaii

divisions

from

the

_{Montana Power Company, which}

operates

large

number

of

hydro

-electric_plantsinthe region;

and

th<

INTRODUCTORY

7

followingmanner. Iftheloadfactor in

any

month

isless

than

60 percent.,

payment

tobe

made

at adefinite price (6'36

mils,_{perunit) for auniform load equal}to_{60 per}cent, ofthe

maximum

5-minutes

peak

; iftheloadfactorexceeds 60 per

cent.,

payment

is

made

atthe

same

rate fortheactual

k.w

load.

_By

means

of

an

efficient systemof train-dispatching,

and

with theaid ofa

number

ofautomatic

and

hand

devices forreducingthesubstation voltage

when

thecurrentis

exces-sive,the_peaksofloadarekept

down and

the loadfactor raised,

sothat in practiceit_nearlyattainsthe60_percent, forwhich

payment

ismade.

As

regenerationisafeature of this road,it

is_probablethat,withoutthese devices,

and

withtrains

worked

without reference to the _supply conditions, the loadfactor

would nothave exceeded 26percent.;

and

the

amount

of

generatingplant requiredto_{have been kept}atthedisposal of

the railway

company would

have been

more

than doubled.

Inthiscasethetrain dispatcherisgiven a widediscretion as

regards

some

ofthetraffic,

and

heisable to useitgreatly to

the_advantageof the railway. Although acontrol so highly

centralized

_may

_{not always be}practicable,itis_verydesirable

inthe interestsof

economy

that thereshould_{be very}intimate

co-operationbetweenthetrafficandoperatingdepartments.

Electric

and

Steam

Locomotives.

The

nature ofthe steam-locomotive_placesitunderdisabilitiesfrom which the

electriclocomotiveishappilyfree Itconsumesfuelaslong

asit isincommission, whetherit isinthe shedor out,whether it ishaulingatrain or standing.

A

large fraction ofitslife is

consumed

in tube-cleaning, oiling,

and

overhauling.

The

electriclocomotive,onthe otherhand, consumes

power

only

when

running,

and

thetimespent in inspection,overhauling

and

cleaning is

insignificant

Much

greater service can

accordinglybegot

from

theelectric

machine

inthecourse of

ayear,

and

the

number

oflocomotivesrequiredto

work

a

giventraffic is correspondinglysmaller. In wintry weather

particularlythesteam locomotivesuffersinefficacy,but the

electric locomotiveretains

and

indeed increases its service

capacity. Experience has

shown

that, in general, half the

number

ofelectriclocomotivesis

more

thanequivalent toa

given

number

ofsteam locomotivesin service capacity.

8

RAILWAY

ELECTRIC TRACTION

ofthesteam locomotive,inthat thelatterisa

power

general

as well as a

power

consumer.

To

put

steam

and

electri'

operation

on

a comparablebasis,thewholechain ofappliam

from power

generating plant to wheels should be broug

under review.

The

essential feature of electrical operati

iscentralizedpower-generation, withdistribution to the

pow

consuming locomotives. Great

power

is therefore at i

disposal ofevery locomotive

on

therailway,andit isthis,

greatmeasure, thatenables electrical operation to deal

w

conditions ofabnormaldifficulty.

In the chainofappliances

which

constitute theworkingpl

of

an

electricrailway, thelocomotive

must

be regardedas1

weakestlink,inthesensethatitislessamenableto adjustm<

than otherparts oftheplant.

The

reason behindthisis tl

the locomotive can only providelimitedspaceforthe_apparat

which

is_{therefore restricted in design, besides}havingtosta

continualvibration; the stationaryplant onthe otherha

isnot_{tied for space,}

and

restson firmfoundations. Give]

satisfactorylocomotive(usingthe

term

to

mean

the

mot

carryingvehiclewhatever

form

it

_may

take), areliablepo^ supply

and

distribution_{system can}

be

devised tosuit;

bu

from any

causethe locomotiveisunsatisfactory,nomerit

therest of_{the plant can}

make

up

forthe_deficiency 11

thereforethebest practice

which

choosesmethodsofoperat

strongatthe locomotive

end

ofthe chain,andadjusts

remainderofthe plantto suitthelocomotive.

System

of

Operation.

The

natureof the plant

wh

connects the prime

movers

with the locomotivewheels depei

inlarge

measure

on

the systemof operation adopted. .

technical characteristics of theseveral systemsin use

describedinalaterchapter;

and

itisthese that ultimat

determine the economicresults

by which

thesystemsaretc

judged. Theseresults

depend

also

on

the circumstances

thecase; and,it

may

be added,

on

the time; fortheGr

War

has

_changed

this, like so

_many

other things Neit

present nor pre-warcosts giveareliable indication to fut

costs.

The

relation between the burden of

capitalexpe

and

_operatingcostis_{particularly conjectural at present}

The

questionofsystemofoperation

must

beviewedbroa(

INTRODUCTORY

9

featuresisaptto_{mislead the judgment.}

-Every

system has

advantages whichare

more

orlessvaluable accordingtothe circumstancesof_{tne particular case. For purposes}ofgeneral

railway operation,however,

two

_{systems only}

need

be

con-sidered,viz.,thecontinuouscurrent system

and

the

single-phase system.

For heavy

urban passengerservice,the former

hasnaturaladvantages;

and

it

would

notbedifficulttopropose

a service of this nature which the latter system

would

practicallybe unabletoundertake.

Apart from

suchspecial

problems, however,it

_may

besaidthat eithersystem could be usedforthe operationofa railwayat

some

cost;

and

the

question of selection resolvesitselfintothe determinationof

theleast costly,having regard bothtoinitial

and

operating

expenses,with due allowance

made

forindirectadvantagesor

disadvantages.

The

_{adoptionof partial}views

by

a few prominentengineers

has resulted in

somewhat

acrimoniousdiscussion ofthesubject

of _{systems of operation,} bothin

England and

in

Am

erica.

Even

beforeasingle-phaserailway

motor

had

been developed,

the_system

had

_{been proclaimed}theonlypossibleonefor

rail-way

working.*

The

developmentofthe

motor

was

therefore

hailedwith an enthusiasm whichitstechnical qualities

by no

means

merited. Cautious designers, studying to perfect it,

saw

that fundamentally it

was

inferior to the continuous

current

motor

;

and had

doubt whethertheadvantagesofthe

system weresufficienttowarrantitsusein theexacting

con-ditions ofrailway service, where the locomotive

motor was

already tried tothe utmost. However,theadvertisemento

thesystemcontinued,and

many

engineerslooked forwardto

itsuniversal adoption.

The

author

was

apparently

among

the

firstpublicly to dissociate himself

from

thisview,showingin

the courseofa_{paper read}in1906_fthat forsuburbanservice

the single-phase system compared unfavourably with the

continuouscurrent system. Thisconclusion,

now

regardedas

commonplace,

was

strenuously contested at the time. Mr.

H. M. Hobart,

who

was among

theearliestadvocatesof_{a high}

voltage continuous current system, did

much

to propagate

sound views onthe subject, insistingon economicas well as

technicalcomparisonof the

two

systems.

*_{See Minutes}

ofProcInst.

C

E

,vol. 49,p 40.

10

RAILWAY

ELECTRIC TBACTION

UnsuitabilityofSingle

-phase

System

for

Urban

Rail-ways.

Time

and

experience being

on

the side of

good

engineering,theenthusiasmfortheuniversaluseof the

single-phase

system waned

as its characteristics

became

better

known.

Itwas, however,

an

episodeinconnectionwith the

electrification ofthe Victorian Railways thatfinallydemolished

itspretensions asappliedtosuburbanservice.

The scheme

was perhaps

the

most

extensivethat haseverbeen undertaken

at a _{singleventure, including}initsscope

more

thanthree

hundred

milesoftrackworkin_{the neighbourhood}ofMelbourne,

11

and

_{involvingan expenditure}ofseveral millionssterling.

The

service contemplated

was

fairly heavy, but

by

no

means

approached thelimit of practicability.

The

engineers incharge

ofthe

work

considereditacase fortheuseofthe continuous

current_system; butstrong influence

was

broughttobearin

the interest ofthe_{single-phasesystem.}

In

order_{to satisfy}

their clients, therefore, the_engineers called for complete

tenders

and

_guaranteesforthe

work

inboth systems, theservice

requiredbeingexactly defined. Tenderswere obtained

from

all_{parts of}theworld,

and

the results of_{the enquiry}are

sum-TABLE

2

marizedintables 1

and

2,*which,however,includeonly the

items affected

_by

_{the question of system.}

The

tables,although

applying to aparticular scheme, are in their

main

features

characteristic ofsuburbanservice.

_By

farthe_largestitemof

expenditureforplantisinanycasethat for_{train-equipments};

and

thisis at leastdoubled inthe single-phase system as

compared withthecontinuouscurrent system. Althoughthe

other items, in theirsum,

show

a balanceinfavourof this

12

KAILWAY

ELECTRIC

TRACTION

system,itis_{insignificant}

_compared

with the adverse balance on the equipment.

The

runningcosts

moreover

are_governed

in largemeasure

by

the itemformaintenanceofcoach

equip-ments, and,sincethisisalsoaboutdoubledinthesingle-phase

system, thetotal

shows

aconsiderablebalance

m

favourofthe

continuouscurrentscheme.

DISTRIBUTION

OF

CAPITAL COSTS IN

URBAN

ELECTRIFICA-TION.

The

pricesatwhichthe contracts in connectionwith

the Victorian

Railways

electrificationwere givenout

may

here

becited (Table3),

not

indeedashaving

any

absolute value at

this date,butas "beingfairlyrepresentative of the proportions

of thevarious items in suburban electrification For this

reason, the several items have been expressedalso_as

per-centagesofthe_{whole, both with generating}plantand

trans-missionlinesincluded

and

withtheseitemsexcluded.

TABLE

3

Table

3

_may

be

_compared

withtable4, whichgivesrelative

itemsofexpense for theelectrification ofthe

Rocky

Mountain

divisions of the

Chicago

Milwaukee

and

St. PaulRailroad.*

*_Given

by

R.Beeuwkes,Electrical Engineer,

CM.

&SP. Ry.,

m

ReportofCommitteeonElectrification ofSteamRailroads, National

Elec. _LightAssociation.,1920. SeeElectricRailwayJournal, 29May,

INTRODUCTORY

13

Thesefigures

may

be takenas typical of

main

linerailways

usingthe high voltage continuouscurrentsystemforworking

heavy

traffic.

TABLE

4

CHICAGO

MILWAUKEE

AND ST.PAUL RAILWAY. ELBOHOTIOATIONCOSTS:

Routemilesrailway

...

. 438

Mileage transmissionlines .

....

364

No.ofsubstations

....

. 14

Total capacitysubstations (k.w.) .

....

69,600

No. ofroad locomotives 42

No.ofswitching locomotives . .

...

2

American

Experience. Reverting to the question

systemsofelectrification, thecontroversy inAmerica was

vigorous as that inthis country,

and

similarly based uu.

preconceptions. Time, however, hasdissolved theillusions

and

littleof the controversy

now

remains.

A

number

of

sections of

American

railroad use the single-phasesystem of

operation,but nowhere with outstanding success. Indeed

Americanexperienceshows nothingto justify thesystem even

when

used for trunk-line service, remote from suburban

territory

THE

SINGLE-PHASE

LOCOMOTIVE MOTOR.

The

weaknessof

the single-phase system, asdisclosed

by

Americanexperience,

lies_principallyin thelocomotive motor, whichis_costlyboth

inmanufacture

and

maintenance.

The

laterdefenders of the

system, indeed, are disposed tothrowover the single-phase

motor,andto relyonthe inductionmotor and phaseconverter,

oron the continuous current motor

and

rectifiertojustify

their position, although the practice

sub-TAE

GENERAL

DATA

AND

MAINTENANCE

COST

OF

MAIN

LINE

ELECT

SION

AND

ANNUAL

BEPO]

ALTERNAT

DIUKC

30MOTIVES

FROM

REPORTS OF INTERSTATE

COMMERCE

COMMIS-LENDAR YEARS

1916-1917-1918

1BNT

IENT

16

RAILWAY

ELECTRIC

TRACTION

stationplant on the locomotive hardlygivespromiseof great

advantage,either infirstcostorrunningcost.

The

comparisonofcostsofdifferentrailwaysystems, unless

conditions of operation are similar,

and

similar

methods

of

accountingareemployed,is_aptto_{be misleading}

and

should not be given

undue

weight. Statistics _compiled to

meet

statutoryrequirements however havevalue,

and

ifused with

sagacity,justifygeneral conclusions. Table5 givesstatistics

ofmaintenancecosts of theelectriclocomotives used

on

a

number

of

American

_{railways, the}figuresbeing taken

from

the_Reportsof theInterstate

Commerce

Commission. Inthis

table,the

New

York

Central, thePennsylvania,

and

the

New

Haven

electrifications

_may

be considered in a general

way

comparable, as being terminal electrifications of

New

York

City.

The

Baltimore

and

Ohio, the Great Northern, the

MichiganCentral,

and

theBoston and

Maine

electrifications arecomparableinbeing local _{tunnel systems.}

The

_Chicago

Milwaukee

and

St.Paul, the Butte,

Anaconda and

Pacific

and the Norfolk

and

Westernelectrificationsarecomparable

as dealingwith

heavy

trainsonsteep gradients. Incidentally

the figures of table 5

show

theeffectofthe

war

in increasing

runningexpense.

INTERURBAN PASSENGER

SERVICE Interurbanelectric

pas-sengerservice,asconductedinAmerica,

was

for

some

years

regardedas particularly suited to takeadvantageofthe merits

of thesingle-phase system,

and

a

number

ofroadswereso

electrified.

The

service is generally intermittent

and

the

distances considerable.

The

trafficisforthe

most

part

worked

by

single cars ofgreatweight.

The

stopsbeingfew, ahigh

rate ofacceleration is notessential.

The

distribution

and

substation costs in such service are proportionately

much

greaterthan incity service. _{Unfortunately, theinferiority}

ofthe_single-phase

motor

has provedthe obstacle to success,

evenhere

The

system shows no advantage overthe

con-tinuouscurrentsysteminsuchservice;

and

indeed

many

of

theroadsinquestion have,after

more

orlessextended

experi-enceofthe_{former system, changed}tothelatter.* Suchaction

on the partofarailway

would

indicatea_{saving in operating}

*

_E

g,,Anderson TractionCo,Annapolis ShortLine, Atlantaand

Marietta, Illinois Traction System, Milwaukee Electric Railway,

INTRODUCTORY

17

expense

by

theconversionsufficient_{to justify}the

heavy

addi-tional

burden

of capitalizationinvolvedin_{the change.}

A

comparison

was

made

some

yearsago, ofoperating

con-ditions

and

_expenses of single-phase

intemrban

roads with

those ofhigh voltage(1,200 volts)continuous currentroads.

The

roads ofthe

two

kindswere chosentobe asnearly as

possible comparable in service conditions,

and

represented

more

than 40 percent,of_{the interurban mileage}oftheclasses

in question existing intheUnitedStates atthetime.

The

investigation established that the _average

number

of

men

employedin car-barns

and

substations, taken together,

was

3 2 per car in service forroads

_{worked by}

the single-phase

system,

and

1*6_percar in service for thecontinuous current

roads.

The combined

running expensesofcar-barns

and

sub-stations, together with maintenance of overhead lines,

was

foundon the averagetobe6'42 centspercar-mile forthe

single-phase system,

and

2'44 cents for thecontinuouscurrentsystem.*

The

_{particular case of the}

_Washington

Baltimore

and

_Annapolis

Railroad,fa road which has

had

experience in

both

systems,

may

becited. La1909,under6,600 volt single-phase operatio]

the

number

of cars

was

23,

and

the

number

of

men

employe,

inthe car-barns63,the car-barnexpenses

amounting

to3*7'

oents per car-mile. In191 1,under1,200 voltcontinuouscurren

operation, the

number

ofcars

was

44, the

number

of

men

smployedinthe car-barns27,

and

the car-barnexpenses

T37

3entspercar-mile. Itisnotremarkablethereforethatfor this

}Jassofservicethe single-phase systemisnolonger considered.

FREQUENCY

INSINGLE -PHASE OPERATION.

American

expe-dience,therefore,justifiesthe opinion of those

who

favour the

'Continuouscurrentsystem;

and

it is

worthy

ofnoticethatof

illcountries the United States alonehas

had

extended

ex-perienceof both systems under railwayconditions, including

heheaviest classesof service. _{Continental engineers,however,}

sxplain the unfavourable results obtained with the

single-)hasesystemin

America

asbeing dueprincipally tothegeneral

iseof_{a frequency}of25_cyclesper secondinstead ofabout 15

ycles,as required for the successful operation ofthe

single-VarrenandJamestown, Washington, BaltimoreandAnnapolis,York

ndHanover.

*

Times Engineering Supplement,Sept. 27, 1911.

18

RAILWAY

ELECTRIC TRACTION

phasemotor. It

must

be admittedthat thereis

some

justifica-tion for thecontention: thesingle-phase

motor

is _severely

limited;

and

the lower the frequency ofsupply, the

more

successfullycanitbedesigned, until at zerofrequencyit_merges

inthe continuous currentmotoritself. Thisis well

under-stood

by

designers,

and

indeed thefirstproposal of

single-phaseoperation in

America was

at 16-_cycles.*

The

Visalia

Electric Railway is moreover operated single-phase at 16

cycles; andthePennsylvania experiments were conductedat

the

same

_frequency,f Nevertheless the additionalexpense

and

other_{grave disadvantagesof generation at} thelow

fre-quency have caused the higher frequency to

be

generally

accepted

by American

engineers asthelesser evil.

The

Continental

_Development.

The

single-phasesystem hasbeen developedrationally in

Germany and

othercontinental

countries.

The

limitations of the locomotive motors

have

been dulyrecognized,

and

the wholeinstallationdesignedin

conformitytherewith. Motors_{of large capacity areemployed,} themotive

power

of_{the locomotive being concentrated}in

one

or

two

motors only; althoughthisinvolvesthe useofside

rod typesoflocomotive.

Power

issupplied ata frequencyof

15 or 16} cyclesper second;

and

is,in general,generatedat

the frequencyof_supply; sothatthe useof rotatingmachinery

betweengenerators

and

trainsisavoided.

Under

these

con-ditionsitisclaimed thatdisabilitiesunderwhich the

single-phasesystem has

been found

tosufferelsewhere, arenolonger

oppressive,

and

the simpledistribution_arrangements

accord-ingly restorethe balanceinfavourof _{the system.}

Unfortun-ately no adequate statistics are available in_support ofthe

claim. _{Unfortunately}also,comparable experiencewith the

rival system,

under

railwayconditions, isalmostlacking in

thecountries

where

the single-phase system has reachedits

highestdevelopment.

BUREAUCRATIC ENGINEERING.

To

theseeker aftertruthit

isalittledisconcerting to find differentcommunities arriving

at differentconclusions

on

fundamental mattersoffact. In

detailssuchdifferencesare to_{be expected}; theyareaccounted

for

_by

differencesinlabourcosts,inthe_{general level of}skill

and

educationofthe

workmen,

in

_temperament

_{of public}

and

*_{TransactionsA.I.E.E., Vol.}

20,page16.

INTRODUCTORY

19

staff,

and

in othersuchnational characteristics. Thereare,

however,

no

differences _apparentin operating conditions in

normalcivilizedcountriessufficientto accountfor anentire

changeineconomic values suchasisindicated

_by

adifference in_{systemof operation.} It_{might be imagined that}thematter

was

reallya

somewhat

indifferentone,wereitnotthat,where

direct comparison has been

made

between the systems, the

results_{have always proved}decisive. There is, however,

an

aspect of the matter

which

should be kept in mind.

The

management

ofa railwayisa_large

_{and complex}

_organism,

with a natural tendencytobureaucracy,

and

itsefficiencyis

usually

most

inevidence

when

itisable tokeepina familiar

groove. In breaking

new

ground,itisasapt as

any

other

human

institutiontobecarried

away by

the

most

confident

ofitsadvisers.

But

_{once having decided}

_upon

acourse,

and

involved itself_{in great expense,}itcanrarely reconsider the

matter; for, besides the economic, there are _very

human

issues involved. In the case ofrailwaycompanies fettered

only

by

commercialconsiderations,economicpressure

may

in

the longrun berelied

upon

to exert

some

_rightingeffort; but

wherethe railways are

owned and

operated

by

theStateeven

this influence will be of little avail.

Under

such auspices

indifferent_engineeringis_likelytobe perpetuated; for there

isnoneto questionit.

But

it isthePrussianStateRailways

thathaveled thedevelopmentofthe_{single-phasesystem}in

Europe;

and

itisnottoo

much

tosay thattheopinionofits

engineer has been largely responsible for the Continental

developmentof_{the system.}

The

biased attitude ofthe

German

authorities towards the question,

may

be judged from the

following recentstatement,* reported to be official:

"

The

German

Federal Railway Administration has alwaysconsidered

the single-phasesystemastheonly one possible forits

main

lines

and

hasnever,eventemporarily, considered

any

other."

Apart from the State Railways there is no unreserved

acceptance of the single-phase system in

Germany.

The

Hamburg

Elevated

and Underground

Electric Railwayis

an

urban

and

suburbanlinewhichparallelsin parts the

single-phase Blankeneseline,

and

dealswith asimilarclassoftraffic. Itis,however,of

more

recent installationthanthe Stateline,

having been openedfortraffic in 1912.

The

concession for

*

Deutsche AllgemeineZeitung,

May

14,1921, quoted fromElectric

20

RAILWAY

ELECTRIC

TRACTION

equipping

and

operatingtherailwaywas grantedtoSiemens

and

Halske

and

theA. E. G. jointly;

and

itis worked

by

the continuouscurrent _systemat 800volts.

However

the

main

Continental development ended with

theoutbreakofwar*,

and

much

water has flowedunderthe

bridges since then. Outside of

Germany

thereis_generallya

wholesome tendency to _investigate the merits of the rival

systems before declaring in favour of either.

The

French

Government

recently appointed a Commission to consider

the question as regardsits

own

railways;

and

thisCommission,

afterverycareful

and

full_{investigation, reported}strongly in

favour of a continuous current _system atmoderately high

voltage.*

The

Belgian

and

the Netherlands Governments

have also_investigatedthematter,

and

have

come

toalike

decision.

The

'Swedish

Government

has the matter under

consideration at the time of _writing.

The

conditions in

Sweden,it

_ma^

be remarked, andparticularly in theNorthern

provinces,favourthe single-phasesystem;

and

the decision

toextendthe'electrification oftheRiksgranslinetoLuleaon

this_system,hasallthe_appearanceofsoundengineering, quite

apart fromthe interestvestedinthe_system

_by

the existing

electrification. It is, however, the lines of the Southern

provincesthatare atpresent underconsideration; andhere,

although the population is sparce

by

comparison with the

countries of

Western

Europe,it issufficientlydense to render

the choice of the single-phasesystemofdoubtful _expediency.

Littlehas_{transpired of theNorwegian} attitudetowards the

subject, for the natural extension of theRiksgransline from

theSwedish bordertothe ice-freeportof Narvik cannot be assumedto indicateageneralpolicy. Switzerlandis

appar-ently committed to the _single-phase system.

The

British

authorities,through the

medium

of_{an Advisory Committee}

ofthe Ministry ofTransport, whichstudiedthematterin all

its_aspects,have decidedinfavour of the continuous current

system,with apreferredline_{pressure of 1,500}volts, permitting,

however, amultiple or sub-multiple ofthis figurewhere local

conditions

demand

it.

As

regardsextra-European countries,

otherthanthe States,it isofinteresttonote thatbothBrazil

and

Chilehave adoptedthat high voltage continuous current

system for extensive electrification schemes. The South

African_{Railways have} also_adopted thissystem.

CHAPTER

II

THE LOCOMOTIVE

The

motive apparatusfor electric trainsis in

some

cases

preferably distributedthroughthetrain,employing the coach

axles as drivingaxles,

and

in other cases

more

advantageously

collected in_{locomotives designed}forthesole_purposeof

accom-modatingit. _{In suburban passenger}service,ifthefull

advan-tageofelectrical_working istoberealized, the multiple unit

operation of

motor

coachesis essential,

and

this _disposition

ofthe_{motive apparatus can}oftenbe

employed

with

advan-tage in otherclassesofpassengerservice;although the extent

to whichit is economicalto use it depends largely

on

the

systemof_{operationemployed, being}

greater inthecontinuous

currentsystem thaninthe_single-phasesystem,

and

leastof

allinthe_polyphasesystem. For goodstraffic

and

for

high-speedlong-distance passenger traffic,

on

the otherhand, the independent locomotiveisthe_preferable

and

in factthe only

practicable

means

of _applying tractive force to the trains.

From

the presentpointof view,however, whichisconcerned

ratherwith the mechanicalfeatures of the drive than with

economy

of operation,it isunnecessaryto distinguishbetween

thelocomotive

and

the

motor

coach, foralthough thelatter

isburdened withcertainrestrictions

which

theformerescapes,

theserestrictionsareofsolittle_{consequence that locomotives}

are frequentlydesignedto

employ

the

same

_type

and

arrange-ment

ofdrive asisused

on

themotorcoach. In thepresent

work, therefore, the term "locomotive"

_may

be taken as

including

"motor coach"

whereverthematteris_applicable

tothisform.

Like

most

human

contrivances, theelectric locomotiveis composedofelementswhich haveusually toeffect_a

compro-misebetween

more

orless _conflicting ideals,

and

the extent towhichit isadvisable toallowthe various ideals to influence

22

RAILWAY

ELECTRIC

TRACTION

the design

and

construction depends

on

the circumstances

and

_particularlyon the systemof operation

and

theclass of

service for -whichthe locomotive isto beused.

Much

isto

be learned in this_{regard from} experience with the steam

locomotive, although, as will readilyberealized,theelectric

locomotive_{presents otherproblems}

and

hasitslimitations in

other directions.

Much

is alsotobe learned

from tramway

experience,

and

in fact

some

of the

most

successfulelectric

locomotiveshave been developeddirectly

from

suchexperience.

An

uncritical description of existing electriclocomotives would

failtofurnishareliable_guidetothe

most

desirable practice;

for

some

are

known

to be _{unsatisfactory,}

and

compara-tivelyfewhave passed the test of _having been duplicated

at later date.

Such

a condition of affairs is of course to

be expectedin_{the early stages of}

_development

ofadifficult art.

CLASSIFICATION

OF

LOCOMOTIVES

The

number

of _types of electric locomotives that have

been developedislarge,

and

itisa matterof

some

difficulty

toclassify

them

clearly. They, however, admitof_{a primary}

division into

two

categories, namely, those in which the

driving axles areactuatedeach

by

a separate motor,

and

those

in whichthese axles are _grouped

and

driven collectively,

through the

medium

of side coupling rods,

by

one or

more

motors.

Individual Drives.

SINGLE

REDUCTION

GEARING. In

locomotives having independently drivenaxles,thecommonest

form

of drive employs single reduction gearing, withthe

motor

suspended

between

axle

and

transom. This

method

a

development

from tramway

practice isinuniversal use for the

motor

coachesofmultiple unittrains,

and

isstillthe

commonest

forlocomotivesof

moderate

speed

and

capacity.

Kg.

1shows the usual arrangement ofthe

motor

in

which

the_gearingis

entirely atone end, whilstfig. 2

shows

an

arrangement

now

frequently

employed

with powerful motors, in which twin

gears are used.

The

unsymmetrical drive offig. 1 tendsto

wear thejournal

and

linings atthe pinion endofthemotor

more

than,

and on

the oppositesideto,thoseatthecommutator

THE

LOCOMOTIVE

23

Fict.1. _{Assembly Drawingof}

24

RAILWAY

ELECTRIC

TRACTION

THE

LOCOMOTIVE

25

withthe axle

and

increasingthestresses attheinside

end

ofthe

gearteeth.

The

gearfacewith_largemotorsisusually

made

some

5 inches to 5 inches wide,

and

increase in

width beyond

thisdoes_{not, in practice, increase}theeffectivetooth strength

appreciably.

The

arrangementof_fig. 2

makes

betteruseof

the material oftheteeth,

but

withrigidgearsresults in

inde-terminate toothstresses,

and

accordinglyrequiresvery accurate

Fio.3 Spring Gearing

fittinginorder to

make

the

two

setsofgearingengage with

approximately equal stresses.

The

need of such extreme accuracy

may

beavoided

by

theuseof right

and

left-handed helical

gears, between which the armature floats. Another

means employed

with the

same

objectistotransmit theforce

from

gears to axlethroughspringswhich

by

permitting

26

RAILWAY

ELECTRIC

TRACTION

ofthe use oftwingears aretobe foundintheChicago Milwaukee

and

St. Paullocomotives, theButte,

Anaconda

andPacific

locomotives, the Detroit River tunnel locomotives, theSt.

dairtunnel locomotives,theHoosac tunnellocomotives,

and

the Shildon-Newportlocomotives.

QUILL

DKIVB. In

some

cases the axle-gears are

mounted on

sleeves orquills

which

surround theaxleswith adequate

clear-ance

and

drivethewheels throughsprings(fig.4).

With

this

construction, sincethe axlebearings are carried

by

thequill,

it ispracticable to

mount

themotor abovetheaxle, asisdone

inthe

Hoosac

tunnellocomotives,

and

in

_many

ofthe

New

York,

New

Haven

and

Hartfordlocomotives. Quillmounting

4. GearedQuillDrive

is

particularly useful inconnectionwithsingle-phase motors,

the elastic transmission _serving to cushion the impulsive

stressesofthe driving forceswhichfalltozero or reverse twice

ineachperiodofalternation.

By

theuse ofthisconstruction

substantially uniform tractive effort is maintained at the

wheels, whilst the

heavy motor

is_{supportedelastically}andthe

gear teeth relieved ofshocks;

and

onthis accountthe

con-structionis_frequently

_employed

even

when

_{the single-phase}

motorsare carried horizontally, as in the

New

Haven

motor

coaches.

GBAELBSS

DEIVB.

Another

method

extensively used for

driving locomotive axles _{independently, employs gearless}

motors havingtheir armatures

mounted

_{concentrically}with

THE

LOCOMOTIVE

27

originally used

on

the Central

London

Railway, the whole

motor

was

carried directlyon theaxlewithout theintervention

of springs. Thisconstruction

would

not

now

be considered

good practice,

and

in

fact, the locomotives

in question wereearly

superseded on account

ofthe excessive

pound-ingeffectofthe

_heavy

uncushioned

masses.

In the

Grand

Central

Terminal locomotives

ofthe

New

York

Cen-traland

Hudson

River

Railroad,

and

in

some

of theC.M.

and

St.P.

locomotives,the

arma-ture of the driving

motor is_{built directly}

onthe axle,whilstthe

field structure is

car-riedonthelocomotive

frame, the

motor

_being

bipolar

and

so

con-structed that exact

adjustment

between

armature

and

field in

a vertical direction is

unnecessary. Fig. 5is

a drawing of one of

the

New

York

Central

locomotives in part

section,

and

shows

how

the motors are

mounted;

figs. 58

and

59

show

longitudinal

and

transverse

sec-tions of such bipolar

motors. Inthe

New

York,

New

Haven

and

Hartford

Rail-road passenger locomotives of the first type, the

motor

is

28

RAILWAY

ELECTRIC

TRACTION

built

up on

a quill surrounding the axle,

and

driving

through, springs.

The

whole

motor

IB therefore elastica

supported; butthisconstructionhas not beenrepeated. 1

gearless

method

ofindependentdrivingisparticularly appj

able tohigh-speed locomotives operating

on

continuouscurrc

systems, for

which

motors

can

readilybe designedto

ms

effectiveuseof thematerials of construction.

Collective Drives. Locomotives, the axlesofwhich t

driven collectively

by means

of side _coupling rods,exhi

greater diversity inarrangement thanthose_havingindept

dently driven axles.

_They

admit, however, of sub-divisi

intotwo

main

_groups; namely, thosein

which

thepower

FIG.6 Side-Rodand JackShaft Drive.

transmitted,

and

therelative

motion

ofthe parts determinec

by

the aid of suitable auxiliary axles orjackshafts,carriedi

bearings inthe

main

frame

about on

the levelofthewhee

axles,fig. 6,

and

thoseinwhichauxiliary axles are absentan

the transmissionto the wheelsis_{effected directly}

_by

the aidc

triangular side-members, usually called "Scotch Yokes"ii

this_{country,*fig. 7.} Inthese locomotives,it

_may

benoticed

themotorsare carried

on

the

main

frames,thus_{being entireh}

spring-supported

from

the axles;

and

a primary requiremen

*_The

Scotch yokedriveisgenerallyknownon the Continentasth< Kandodrive.

THE

LOCOMOTIVE

29

ofthe transmission_systemisthatitshould

be

arrangedso as

notto interfereappreciably with the freedomofthe driving

axles as regards displacement in a vertical direction.

The

side-rods,coupling the wheels with thejackshafts,are

accord-ingly inall_{cases sensibly horizontal,}

and

_{so jointed as to}allow

the necessaryfreedom. In the Scotch

yoke

drive,moreover,

the crank-pinbrasses ofthecentralwheels are

made

freeto

work

inaverticalslotinthe yoke, with the

same

object.

These

featuresare

shown

clearly infigs.6

and

7

and

inthe

illustra-tionsgiveninthe appendix.

Where

a groupofaxlesaredriven

from

asinglemotor, the

transmission has hitherto usually been through quartered

connecting-rods

and

jackshafts,

and

many

locomotives

have

been constructed ontheselines.

The

Pennsylvania

and

the

FIG 7 ScotchYokeorKando Dnve

Dessau-Bitterfieldlocomotives

_may

becited as typical

exam-ples. In the earlier Lotschberg locomotives, however, the

transmission to thejackshafttakes placethrough gears;

and

this_{practiceappears}toberevivingandspreading.

Sometimes

iwo motorsareusedinconnection with asinglejackshaft,

jhe later Wiesental locomotives _(Baden State _Railways)

'urnishingan exampleinwhichconnecting-rods are used,

and

/heNorfolk

and Western

locomotives

_{an example}

in which

;earsareusedtotransmit the

_power

tothe jackshaft.

Some-imes,onthe otherhand,

two

motorsareusedtodrivea group

>fwheels_through

two

jackshafts, as intheearlierWiesental ocomotivesofSiemens-Schuckert, and the Midi locomotives

iesigned by the A.E.G. In the Scotch yokedrive the

two

aotor-shaftsare usuallyconnecteddirectly

by means

ofthe

30

RAILWAY

ELECTRIC TRACTION

yokes,which transmit the

power

to thewheels; thisisthe case

intheGiovi

and

Simplon locomotives

and

many

others; inthe

laterLotschberglocomotives,however, the motorsare_geared

to

yoked

auxiliaryshafts.

DiSTBiBUTiotf

OF

TYPES. Collective drivinghasfoundless

favour

_among

American

engineers than on the

European

continent, forhaving taken theleadingpartinthe development

ofthecontinuous currentsystemof_{railway operation,they}

follow natural

and

sound lines of evolution in _preferring

methods

which experience with this _system has justified.

Many

continental engineers

on

theother

hand

have convinced

themselves that

main

line electrification is essentially

an

alternating currentproblem,

and

have developedlocomotives

with particular reference tothelimitations imposed

by

the

corresponding system of operation. Possibly, however, the

differenceisin

some

measure

an

accidentofdevelopment,for

the

New

York,

New

Haven

and

Hartfordlocomotives, thefirst

single-phaselocomotivesof_consequencetobe

made

inAmerica,

were under thenecessity ofrunning both onsingle-phase

and

continuouscurrentlines.

The

single-phasemotor, on account

oflimitations of design,has

an

armature

wound

forabout300

volts,

and

inordertouseit

on

a600-voltcontinuouscurrent

system atleastfour motors are required as acontrolunit;

thisfavours independentdriving ofaxles.

The

motorsofthe

New

Haven

locomotivesare,asabove mentioned,forthe

most

partcarried

on

the locomotive framedirectlyabovetheaxles,

and

are_{geared each}toaquillsurroundingthe axle withdue

clearance

and

_drivingit_throughsprings.

A

siderodlocomotive

drivingthrough aquill,aninclined connecting-rod,anda jack

shaftwas, however, suppliedto the

New

Haven

railway,but

has _{apparently proved} unsuccessful,

and

this _experience,

togetherwith thetroublesthathavearisen inconnectionwith

European

side-rod locomotives,has probably tendedtodeflect

American

_development

from

_{the typ}e. Itis_worthyofmention,

however, thatthe chief

_example

_among

powerfullocomotives

oftheuse of side-rod drivewith continuouscurrent motorsis

American, being thatof_{the Pennsylvania Railroad}locomotives, of which thirty-three are

employed

for passenger trafficin the

New

York

tunnel

and

terminalservice.

THE

LOCOMOTIVE

31

singleunit, or

may

consist of

two

units _arranged to be

employedtogether.

With

respect to thewh&el system, the whole weight

may

becarriedondrivingwheelsor_partofit

may

be on runningwheels.

The

drivingwheel baseof

_any

unit

may

itselfbe a_{rigid unit, or}it

_may

be dividedinto sections

correspondingto as

many

trucks,

and

capable of swivelling

with _respect to each other.

The

trucks

_may

be connected

togetherthroughtheir centre pins

and

theunderframeofthe

cab, as inthe ordinary

motor

coach; or in the Metropolitan

Railway locomotives;

and

inthiscasethe

draw and

buffinggear

isusually carried on the underframe; or_they

may

be

con-nected

_{by means}

ofa

draw

baras intheNorth-Eastern Railway,

Shildon

&

Newport

locos,or

_by

a mallethinge, as inthe Detroit

RiverTunnellocos,

and

in these casesthe

draw and

buffing

geariscarried on the truckframes.

Although

by

no

means

exhausting thepossibility of variation

intheelectriclocomotive,theabove remarks

show

how

great

the variety is,

and

although

some

types are doubtless

ephemeral, there are neverthelessa

number

of types which

exhibit signs ofpermanence.

With

afew exceptionsit

_may

besaidthat_{locomotives havingcollectively}drivenaxles pertain

to alternating-current systems, that of these,those

which

use

jack-shaft drive pertain to single-phase systems,

and

those

whichusetheScotch yokedrive pertain topolyphasesystems.

The

ultimatereasons forthe_development

and

distribution of

the types

must

_{be soughtpartly in the properties of}thedriving

motorsas affecting their essential designunderthe limitations

imposed

by

locomotiveservice,partly in the class ofservice,

partly incustomary

methods

ofhandlingtraffic,partly in the

nfluence ofsteam locomotive_engineers,

and

partly in

some

jasesinbureaucratic prejudices.

Classification

by Wheel

-arrangement.

Itwill_perhaps

issistintelligentdiscussion of the subjectif_{a system}of

classifi-ation according towheel-arrangementishere_explained.

The

ystemusually employedin

England and America

has been dopted from steam-locomotive _practice; but it does not

urnishthe

same

informationas inthe case ofthe

steam

loco-aotive,particularly

when

the axles aredriven

by

independent

lotors. In thefirstplace, the distinctionbetween

driving-r_heelsand

guiding-wheelsisfrequentlylost, sincethe

same

r