Unit-I.Regenerative Breaking System, Mechanical Engineering seminar

Mechanical Engineering

1. TYPES OF SERVICES
1. Main line service.
2. Urban or city service.
3. Suburban service.
Speed time curve:
1. Constant accelerating period.
2. Acceleration on speed curve.
3. Free-running period.
4. Coasting period.
5. Braking period.
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3. Average speed
Itisthemeanofthespeedsattainedbythetrainfromstarttostop,i.e.,itis
definedastheratioofthedistancecoveredbythetrainbetweentwostopsto
thetotaltimeofrum.Itisdenotedwith‘Va’.
Scheduletime
Itisdefinedasthesumoftimerequiredforactualrunandthetimerequiredfor
stop.
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4. The factors that affect the schedule speed of a train are:
1. Crest speed.
2. The duration of stops.
3. The distance between the stops.
4. Acceleration.
5. Braking retardation.
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5. 6/27/2024 K.Karthikeyan 5

6. Braking
Theprocessofbringingthemotortorestwithinthepre-determinedtimeis
knownasbraking.
Agoodbrakingsystemmusthavethefollowingfeatures:
•Brakingshouldbefastandreliable.
•Theequipmenttostopthemotorshouldbeinsuchawaythatthekinetic
energyoftherotatingpartsofthemotorshouldbedissipatedassoonas
thebrakesareapplied.
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7. Theadvantagesoftheelectricbrakingoverthemechanicalbraking
oTheelectricbrakingissmooth,fast,andreliable.
oHigherspeedscanbemaintained;Thisleadstothehighercapacityofthe
system.
oTheelectricbrakingismoreeconomical;
oHeatproducedintheelectricbrakingislessandnotharmfulbutheat
producedinthemechanicalbrakingwillcausethefailureofbrakes.
oIntheelectricbraking,sometimes,itispossibletofedbackelectricenergy
duringbrakingperiodtothesupplysystem.Thisresultsinsavinginthe
operatingcost.Thisisnotpossibleincaseofmechanicalbraking.
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8. Dissadvantages
•Duringthebrakingperiod,thetractionmotoractsgeneratorandelectric
brakescanalmoststopthemotorbutitcannotholdstationary.Hence,itis
necessarytoemploymechanicalbrakinginadditiontoelectricbraking.
•Tractionmotorhastoworkasageneratorduringbrakingperiod.Sothat,
motorhastoselectinsuchawaythatitshouldhavesuitablebraking
characteristics.
•Theinitialcostoftheelectricbrakingequipmentiscostlier.
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9. 1.Electricbraking-thekineticenergyoftherotatingpartsofthemotoris
convertedintoelectricalenergywhichinturnisdissipatedasheatenergy
inaresistanceorinsometimes,electricalenergyisreturnedtothesupply.
2.Mechanicalbraking-thekineticenergyoftherotatingpartsis
dissipatedintheformofheatbythebrakeshoesofthebrakeliningthat
rubsonawheelofvehicleorbrakedrum.
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10. TYPESOFELECTRICBRAKING
1.Plugging.
Theelectricmotorisreconnectedtothesupplyinsuchawaythatithas
todevelopatorqueinoppositedirectiontothemovementoftherotor.
2.Rheostaticbraking.
Theelectricmotorisdisconnectedfromthesupplyduringthebraking
periodandisreconnectedacrosssameelectricalresistance.
3.Regenerativebraking.
Thekineticenergyofthemotorisconvertedintoelectricalenergywhich
isfedbacktothesupplysystems.
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11. TRACTIVEEEFFORT(Ft)
Itistheeffectiveforceactingonthewheeloflocomotive,necessaryto
propelthetrainisknownas‘tractiveeffort’.
Ft=Fa+Fg+Fr
1.Requiredforlinearandangularacceleration(Fa).
2.Toovercometheeffectofgravity(Fg).
3.Toovercomethefrictionalresistancetothemotionofthetrain(Fr).
Gearratio=Speedofmotorpinion/Speedofdrivingmotor
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12. SPECIFICENERGYCONSUMPTION
Theenergyinputtothemotorsiscalledtheenergyconsumption.Thisisthe
energyconsumedbyvariouspartsofthetrainforitspropulsion.
Theenergydrawnfromthedistributionsystemshouldbeequalstotheenergy
consumedbythevariouspartsofthetrainandthequantityoftheenergy
requiredforlighting,heating,control,andbraking.
Thisquantityofenergyconsumedbythevariouspartsoftrainpertonper
kilometerisknownasspecificenergyconsumption.Itisexpressedinwatt
hourspertonperkm. 12

13. Factors affecting the SEC
1.The distance between the stops
2.The acceleration and retardation
3.The maximum speed
4.Gradient
5.Train resistant
6.Type of train equipment
Home work
1.Anelectrictrainisacceleratedat2kmphpsandisbrakedat3kmphps.
Thetrainhasanaveragespeedof50kmphonaleveltrackof2,000min
betweenthetwostations.Determinethefollowing:
1.Actualtimeofrun.2.Maximumspeed.
3.Thedistancetravelledbeforeapplyingbrakes4.Schedulespeed.
Assumetimeforstopas12sec,andrunaccordingtotrapezoidal.
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