TRACTION MOTORS in Electric Traction.ppt

Traction Motors

1. TRACTION MOTORS
•SeriesandCompoundmotorsareemployedind.ctractionsystems
•Whereassinglephaseseriesandthreephaseinductionmotorsare
usedina.csystems.
Featuresoftractionmotors:
Mechanicalfeatures:
Lightinweightandsmallspacerequirement
Robustandshouldbeabletowithstandvibrations.
Totallyenclosedespeciallywhenmountedbeneaththelocomotive,to
provideprotectionagainstingressofdirt,dust,water,mudetc.
ElectricalFeatures:
Highstartingtorque
Simplespeedcontrol
Possibilityofdynamicorregenerativebraking
Capabilityofwithstandingvoltagefluctuations
seriesspeed-Torquecharacteristic
Bettercommutation

2. Motors employed in Traction
1.D.Cseriesmotor
Advantages:
Highstartingtorque
Simplespeedcontrol
Bettercommutationuptotwicefullload
Simpleandrobustinconstruction
Lesssusceptibletovariationsinsupplyvoltage
Capableofwithstandingexcessiveloads.
Disadvantages:
Ithasnumberoflimitationsoverspeed,voltageandcurrent.
Thereisariskofflash-overandthebrushgearrequires
moremaintenance
Thesemotorsaremoreparticularlysuitableforsuburban
andurbanserviceswherehighrateofaccelerationis
essential.

3. A.C Series motor
Manysinglephasea.cmotorshavebeen
developedfortractionpurposesbutonly
compensatedseriestypecommutatormotorisbest
suitedfortraction.
Singlephaseinductionmotorsarenotcapableof
developinghighstartingtorquehenceitisnotused.
Advantages:
Higherefficiency
Improvedcommutation
TheweightperKWoutputisgreaterforthehigher
frequencybecauseoflargerdimensionsofthe
motor.
Efficientspeedcontrolofmotorbyprovidingtapson
atransformerwhichisnotpossibleind.cseries
motor.

4. A.C Series motor...
Disadvantages:
Lowpowerfactoratstartingandon
overloadsduetohighinductivenatureofthe
seriesfieldandarmaturecircuits.
Lowstartingtorqueduetolowp.fatstarting
Constructioncostismorethanthatofad.c
seriesmotor.
Thesemotorsareusedformainline
services.Thesearenotsuitableforurban
andsuburbanservicesbecauseoflow
startingtorqueandpoorp.fatstart.

5. Three phase induction motor
•Though3-phaseIMhavetheadvantagesofsimple
androbustconstruction,highvoltageoperation,less
maintenanceetc,theyarenotusedfortractionwork
duetotheirflatspeed-torquecharacteristics,
constantspeedoperation,lowstartingtorqueand
complicatedoverheadfeedingsystem.
•Intractionsystememploying3Φinductionmotorsit
becomenecessarytocoupleallthedrivingaxles
throughaconnectingrodsothatthereisno
possibilityofadifferenceinspeeds.
•Withthedevelopmentofthyristorisedinverter
circuits,itisnowpossibletoinvertthesupplyand
obtainavariablefrequencysupplyandsmooth
speedcontrolcanbeobtainedin3Φinduction
motors.

6. Traction motor control
Needfortractionmotorcontrol:
Startingwithoutdrawingexcessivecurrent
fromthesupply
Smoothaccelerationwithoutcausing
suddenshocksoastoavoiddamageto
thecouplingsandinconveniencetothe
passengers.
Speedcontrolasperrequirements.
Providingrheostaticorregenerative
braking.

7. Multiple control
•Thecoacheswhicharefittedwithtractionmotors
arecalledmotorcoaches.
•Themotorcoachesareusuallyemployedincityand
suburbanservice.
•ThelengthofthetraindependsupontheNo.of
motorandtrailercoachedemployedwhichof
courseisdeterminedbytheNo.ofpassengersto
becarried.
•TheNo.ofmotorcoachesdependsuponthetraffic
requirements.
•Thus,duringheavytrafficperiod2ormorethan2
motorcoachesandanumberoftrailercoachesmay
berequiredwhereasduringoff-peakperiodsone
motorcoachandonetrailermaybegoodenough.

8. Multiple control….
•Eachmotorcoachmayhavetwoorfourmotorsandmust
becapableofcontrolfromasinglepointandthiscontrol
systemisknownasmultipleunitcontrol.
•TheequipmentsprovidedinmotorcoachesareMaster
controller,SeriesParallelcontroller,andMulti-corecablefor
controlcircuits,Acceleratingrelays,Reverser,Starting
resistanceandcollectorgear.
•Thecontrollersandreverserarecontrolledbyamaster
controllerinthecabofanymotorcoach.
•TheequipmentsrequiredonthetrailercoachareMaster
controller(ifrequired),Multi-corecablewithcouplesockets
forthecontrolcircuits.
•Themotorcoachisalsoprovidedwithcertaindevicesfor
theprotectionofmotorsagainstoverloads.Theseconsists
ofovercurrentrelaywithDriver’scontrolswitch,isolating
switchformastercontroller,switcheswithfusesforisolating
thecontrolcircuitoftheMotorcontrollerfromthecontrolbus
line.

9. Multiple control….
•Withalltypesofcontrollers,aDeadMan’shandle
deviceisprovidedinordertostopthetrain
automaticallyincasethedriverfailsand/ornotina
positiontocontroltheoperation.
•Thisisintheformofacontactattachedtotheknob
ofthecontrollerHandle.
•Ifthedriverisnotabletooperatethehandle
properly,theknobriseswhichcausesthecontactto
closeandoperatethemaincircuitbreakerand
applythebrakes.

10. Braking
•Inelectrictraction,bothelectricalandmechanical
brakingisemployedforbringingthevehicletorest.
•Inelectricbraking,thebrakingenergyisconverted
intoelectricalenergyandeitherdissipatedinthe
resistancesmountedonthevehicleorreturnedto
thesupplysystem.
•Itgreatlyreducesthewearofthebrakeshoes,
provideshigherretardation,thusbringingavehicle
quicklytoahalttherebytherunningtimeis
shortenedtoaconsiderableextent.
•Inregenerativebraking,apartofbrakingenergyis
returnedtothesupplysystemtherebyaffecting15
to20%savinginenergyconsumption.

11. Basic requirements of a braking systems
•Itshouldbesimple,robust,quickandreliablein
action
•Easytousefordrivertooperate
•Maintenanceshouldbeminimum
•Thebrakingsystemshouldbeinexhaustible
•Incaseofemergencybraking,safetyconsideration
istakenintoaccount.
•Kineticenergyofthetrainmustbestorableduring
brakingwhichcouldbeusedsubsequentlyduring
accelerationofthetrain.

12. Advantagesofelectricbraking:
Lessmaintenance
Smoothbraking
Nodustisproduced
Replacementandadjustmentofbrakeshoes
iseliminated
Heatenergyisfedbacktothesupply.
DisadvantagesofElectricalbraking:
Theratingofbrakingequipmentrequiredis
higherthantheratingrequiredformotor
alone.
Additionalequipmentisrequiredinsome
cases
Economicalconsideration.

13. Braking methods
•Therearethreemethodsofapplying
electricbrakingare
(1)PluggingorReversecurrentbraking
(2)Rheostaticbraking
(3)Regenerativebraking