Chapter1-DC-machine-《Electric-Machinery-电机学(英汉双语)》课件

Chapter1

DCMachines1.1Introductiontodcmachines1.2Armaturewindings1.3Magneticfieldsofdcmachines1.4Inducedvoltageandelectromagnetictorque1.5Equivalentcircuitofadcmachine1.6Powerflowandlossesindcmachine1.7Operationcharacteristicsofdcgenerator1.8Operationcharacteristicsofdcmotors1.9Speedcontrolofshuntdcmotor1.10Startingofdcmotor1.11Brakingofdcmotor1.12CommutationBriefContent

1.1.1TheConstructionofDCMachinesDCMachine(Armaturecore)(Armaturewinding)(Brushes)(Brushes)(Commutator)(Shaft)FieldpoleFieldwinding

Thecross-sectionofadcmachine

(interpole)(Fieldpole)(York)(Armaturecore)(Armaturewinding)(Frame)FieldwindingSheetofrotorStatorandRotorAirgapwhichisseparatingstatorandrotorStationarypart:Frame,FieldPoleandBrushes

Rotatingpart:Armaturecore，WindingShaftandCommutator

DCMachinesThearmaturewindingisplacedintherotorslotandconnectedtorotatingcommutatorwhichrectifiestheinducedvoltageThebrusheswhichareconnectedtothearmaturewinding,rideoncommutator

1.1.2OperationPrincipleofDCMachines(sliprings)（brushes）(commutator)（brushes）DCMotors:operationprinciplesSupplyaDCvoltagetothebrushesXandY.1.1.3ExcitationtypesofDCMachines

SeparatelyexcitedDCmachineShunt(excited)DCmachineSeries(excited)DCmachineCompounded(excited)DCmachineDCMotor

＋

－

＋

－

＋

－

他励(Separatelyexcited

)

+-

并励(Shuntexcited)

+

_串励(Seriesexcited)

复励

(Compoundexcited)

－

＋

－

＋

＋

－

他励(Separatelyexcited

)

－

＋

并励(Shuntexcited)

－

＋串励(Seriesexcited)

复励(Compoundexcited)DCGenerator1、Ratedpower：W,kWMotor:theoutputmechanicalpower：Generator:theoutput

electricalpower：2、Ratedcurrent：A3、Ratedvoltage：V4、Ratedspeed：r/min5、Ratedexcitationcurrent：A6、Ratedexcitationvoltage：

V8、Polenumber：

polepairnumber1.1.4RatingsofdcmachinesExample1-1

Adcgenerator,itsratedpowerPN=10kW,ratedvoltageUN=230V,ratedspeednN=2850r/min,ratedefficiencyN=0.85.Calculateitsratedcurrentanditsratedinputpower?Solution:

theratedcurrentofthedcgeneratorisIN=PN/UN=10*1000/230=43.48(A);TheratedinputpowerisP1=PN/N=10*1000/0.85=11765(W).Example1-2

Adcmotor,itsratedpowerPN=17kW,ratedvoltageUN=220V,ratedspeednN=1500r/min,ratedefficiencyN=0.83.Calculateitsratedcurrentanditsratedinputpower?Solution:

theratedinputpowerofthedcmotorisP1=PN/N=17*1000/0.83=20482(W);ItsratedcurrentisIN=P1/UN=20482/220=93.1(A).

1.2ArmaturewindingofDCMachines

Differentconnectionwaysofloopstocommutatorsegments(换向片)affectthenumberofparallelcurrentpaths（并联支路数）,theoutputvoltage（输出电压），thenumberandpositionofthebrushes（电刷的数目和位置）ridingonthecommutatorsegments.Lapwinding（叠绕组，simplexlap-单叠，

multiplexlap-复叠）Wavewinding（波绕组，simplexwave-单波，

multiplexwave-复波）

Lapwinding

Wavewinding

Elementsofalapwindingandawavewindingwithtwoturnsareshown.Windingpitchofalapandawavewinding

Lapwinding

Wavewinding铁芯齿槽楔xie绝缘导体端接有效边SometermsareemployedforbetterdescriptionoftheconstructionofDCarmaturewindings.

Theyarewindingpitch(y),polenumber(2p),polepitch(),slotnumber(Q),windingelementnumber(S),commutatorbarnumber(K),commutator

pitch(yc),thefirstpitch(orcoilpitch)(y1)andthesecondpitch(y2).

Thedistancebetweenthebeginningsoftwoconsecutiveturnsiscalledthewindingpitch(y).Thedistancebetweenthebeginningofoneturntotheendofthesameturniscalledthefirstpitch(orcoilpitch)(y1).Thelengthofthestep

necessarytofollowthrough

fromtheendofoneturntothebeginningofthenextfollowingturnarecalledthesecondpitch(y2).Thedistancebetweenthetwocommutatorbarsconnectingtothetwoendsofanelementwindingiscalledthecommutatorpitch(yc).y=y1y2(lapwinding)y=y1+y2(wavewinding)

y=

yc(lapandwavewinding)Thefirstpitch(coilpitch,y1)oflapandwavewindingsmustbeequalorapproximatelyequaltothe

polepitch

(=Q/2pinslotpitches).

y1=

(lapandwavewinding)whenthecoilpitchy1isequaltothepolepitch

(=0),thewindingisdefinedasfull-pitchwinding;ify1isgreaterthan

(0),thewindingisdefinedasalong-pitchwinding;andify1islessthan

(0),thewindingisdefinedasshort-pitchwinding,andisalsocalledfractional-pitchwinding.y=yc=1(simplexlapwinding)y=

yc=

(K±1)/p(simplexwavewinding)1.2.1Simplexlapwinding

Fora4-polemachinewithfull-pitchprogressivesimplexlapwindinghaving

thesamenumberofwindingelements,slotsandcommutatorbars,i.e.,Q=S=K=16,1.Pitchescalculation

:Forthefull-pitchprogressivesimplexlapwinding,y=yc=1.AccordingtoEq.1-6:y1=

=Q/2p=16/4=4,AccordingtoEq.1-3:y2=y1y=4-1=32.Windingelementsconnection:

3.Developedwindingdiagram:Developedwindingconnectionwith4-polesisshowninbelow.theupperandlowerlayersareshownsidebyside.

Theupperlayerisrepresentedbysolidlineandthelowerlayerisrepresentedbydottedline.theupperlayeroftheelement1isconnectedtocommutatorbar1;thelowerlayerofelement1isconnectedtotheupperlayerofelement2andcommutatorbar2,andsoforth.Thelowerlayerofthelastelement16isthenconnectedwiththeupperlayerofelement1andcommutatorbar1,andthewindingisclosed.4.Placingmagneticpolesandbrushes:ThemagneticpolesareplacedevenlyonthestatorwithNandSalternately,andthepolewidthisusuallyequalto0.75.theaxisbetweentwoadjacentNandSpolesiscalledneutralaxisorquadrature-axis.Thebrushesarepositionedaroundthecommutatorinawaythattheyareconnectedwiththeconductorslyingatthemiddlepointsof

thetwomagneticpoles(NandS).thetwoconductorsofcoil1,5,9,13arelyingatthemiddlepointsofNandSpolesandcoil1,5,9,13areshortedbybrushA1,B1,A2andB2respectively.Theemf

inducedintheconductorsofcoil1,5,9,13issosmallthatthecirculatingcurrentflowingthroughthebrushesisnegligible.Ingeneral,lapwindings

haveequalnumberofbrushesandpoles.5.Instantaneouscircuitdiagram:6.Parallelbranchesofwindings

2a=2p(simplexlapwinding)1.2.2Simplexwavewindings

Fora4-polemachinewithshort-pitchretrogressivesimplexwavewinding,notedthatthenumberofwindingelements,slotsandcommutatorbarsisthesamewitheachother,i.e.,Q=S=K=15.1、Pitchescalculation:Fortheshort-pitchretrogressivesimplexwavewinding,accordingtoEq.1-8,y=yc=

(K1)/p=(151)/2=7.AccordingtoEq.1-6,y1=

=Q/2p

=15/4=3.AccordingtoEq.1-4,y2=yy1

=73=4.2、

Windingelementsconnection:3.Developedwindingdiagram:thefirstwaveisconnectedtocommutatorbar1,8,15;thesecondwaveisconnectedtocommutatorbar15,7,14;thethirdwaveisconnectedtocommutatorbar14,6,13;thefourth,fifthandsixthwaveareconnectedtocommutatorbars(13,5,12);(12,4,11);(11,3,10)respectively.Thelastwaveisconnectedtocommutatorbar10,2,9,andthelastturnisconnectedtocommutatorbar9and1,andthewindingisclosed.Thebrushesareattachedonthecommutatorinawaythattheyareconnectedwiththeconductorslyingbetweentwomagneticpoles(NandS).Ingeneral,wavewindings

haveequalnumberofbrushesandpoles.4.Parallelbranchesofwindings2a=2(simplexwavewinding)1.3MagneticfieldsofDCmachines

NoloadoperationLoadedoperationArmaturereaction1.3.1Magneticfieldinno-loadconditionwecanseethatthelengthoftheairgapbetweenthepoleandthearmatureisnotuniform.Theairgaplengthislargerunderthepoleshoethanthoseunderotherpartsofthepole.Sothefluxdensityintheairgapbetweenpoleshoeandthearmatureissmallerthanthatoftheairgapbetweenpolefaceandarmature.thefluxdensitycurveofaDCmachineatno-loadisaflat-topshapedcurve.aflat-toppedcurve1.3.2

Magneticfieldinloadedcondition

1.MMFofarmaturewindings

ToillustratethearmaturewindingMMF,itisassumedthatonlyarmaturewindings

carrycurrent.

Fieldcurves,i.e.,thefluxdensitydistributionBaxasafunctionofdistancex,aredeterminedbythemmf

Faxcurveandthelengthoftheair-gapδx(orthemagneticreluctance)forthedifferenttubesofforce,i.e.Bax=0Fax/x.Sincethemagneticreluctanceisveryhighintheinterpolarspace,thefluxdensityintheq-axisisverysmall.TheapproximatedshapeofthefieldcurvewhichcorrespondstothemmfcurveinFig.bisshowninFig.c.InaccordancewithFaraday’slawforinducedemf,allconductorslyingundernorthpolewillinduceemfinonedirectionandallthoseundersouthpoleswillinduceemfintheoppositedirection.Ifthebrusheslieintheneutralaxis,thesameruleasthatofthevoltagealsoappliestocurrent,thus,allconductorsabove(orbelow)theneutralaxiswillinducecurrentflowinginthesamedirection.Ifthebrushesshiftawayfromtheneutralaxis,Faraday’slawforemfwillnolongerholdforcurrent.Thisisduetothefactthatbrushespositiondeterminestheparallelcircuits.Sincethecurrentdirectionisthesameforallconductorswithintheparallelcircuits,allconductorsabove(orbelow)thelinedeterminedthebrushesmusthavethecurrentsofthesamedirection.2.Bothfieldwindingsandarmaturewindingscarrycurrentand

Armaturereaction.

(1)Quadrature-axisarmaturereaction

Quadrature-axisarmaturemmfproducesthenon-uniformfluxdistributionwithinapole,andasaresult,theair-gapfluxdensityunderonehalfpoleisgreaterthanthatoftheotherhalfpole.Ifthereislowmagneticsaturationinthearmatureteethandinthepoleshoe,themmfsofthefieldandarmaturewindingscanbeconsideredseparately.Thearmaturefluxdistributionisthenastraightlineunderthepoleandasaddle-shapedcurveintheinterpolarspace.Thefluxdistributioncurveisflat-toppedproducedbythefieldmmfalone.Sincethesaturationofironislow,thearmaturefluxandtheaxisofabscissaaresymmetrical.

Thatmeansthemagnitudeoftheair-gapflux,whichisproportionaltotheareaofthefluxdensitycurve,remainsthesameunderloadasthatofno-load.Ifthearmatureteethandpoleshoesaresaturated,thearealyingabovecurveb0betweencurvebandcurveb0

willbesmallerthanthatoflyingbelowcurveb0.

Asaresultofarmaturereaction,theresultantair-gapfluxunderloadwillbelessthanthatofno-loadandtheneutralaxiswillshiftdegreetotheleft/right.(2)Demagnetizingeffectofarmatures

Ingeneral,fluxcanbeweakenedundertwoconditions:

1)brushesofgeneratorsareplacedinthedirectionofrotation.

2)brushesofmotorsaredisplacedintheoppositedirectionofrotation.Contrarily,fluxcanbestrengthenedby1)brushesofgeneratorsaredisplacedintheoppositedirectionofrotationand2)brushesofmotors

aredisplacedinthedirectionofrotation.1.4Inducedvoltage

andElectromagnetic(Induced)Torque

Voltagegenerated

fromDCmachinesisthesameastheDCvoltagebetweentwobrushes,i.e.,thetotalvoltageofaparallelcircuit.1、theaveragevoltageeavinducedinconductorsBavistheaveragedensityperpole,T;

eavistheaveragevoltageofoneconductor,V;

listheeffectivelengthoftheconductor,m;

visthemechanicalspeedoftheconductorcuttingthefield,m/s,andv=2pn/60,nistherotationspeedofthearmature,r/min.2、TheaveragevoltageEa

betweentwobrushes

CeisthevoltageconstantwhichdependsupontheconstructionparametersofDCmachines,

Nisthe

totalnumberofturnsinseriesbetweenarmatureterminals;nistherotationspeedofthearmature,r/min.Ingeneral,thevoltageof

allrealDCmachinesdependsonthesamefactors:(a)Theperpolefluxinthemachine;(b)Thespeed(n)ofthemachine’srotor;(c)TheconstantCe

withrespecttotheconstructionofDCmachines.Ifthesaturationofironislow,theperpoleflux

canbeexpressedKfIf,where

Kf

isaconstantandIfistheexcitationcurrent.

isthemechanicalspeedofrotor,rad/s,and1.4.2Electromagnetictorque

whenthearmaturerotatesone-poledistance,theaverageforcefavproducedbyconductorsis

Bav:theaveragedensityperpole,T;

l:theeffectivelengthoftheconductor,m;

Ic:thecurrentperconductorinampere;

fav:theaverageforceinnewton.Thetorque(innewton-meter)producedbyasingleconductorofsmootharmatureis

Tavistheaveragetorqueofoneconductor,N.m;Daisthearmaturediameter,m,andDa=2pτ/π.thetotaltorquecanbeobtainedbyaddingupthetorquesofallNconductorsaroundthearmature.

CTisthetorqueconstantwithrespecttotheconstructionparametersofthemachine,Ingeneral,theelectromagnetictorqueofamachinedependsonthreefactors:(a)Theperpolefluxinthemachine;(b)Thearmature(orrotor)currentIa;(c)TheconstantCTwithrespecttotheconstructionoftheDCmachine.Ifthesaturationofironislow,theperpoleflux

canbeexpressedasKfIf,whereKf

isaconstantandIfistheexcitationcurrent.Example1-3:

Adcmotorhasthesimplexlapwinding,thepolepairp=3,thetotalconductornumberN=398,theperpoleflux=2.110-2Wb,Calculatedtheinducedvoltagewhenspeedn1=1500r/minandn2=500r/min?Solution:

Accordingtothesimplexlapwinding,theparallelcurrentpathsaequaltothepolepairp,namely,a=p=3;AccordingtoEq.1-14,whenspeedn1=1500r/min,theinducedvoltageis(V);Whenspeedn2=500r/min,theinducedvoltageis(V).Example1-4:

Adcmotorhasthesimplexlapwinding,thepolepairp=3,thetotalconductornumberN=398,theperpoleflux=2.110-2Wb,CalculatedtheinducedtorquewhenarmaturecurrentI1=10AandI2=15A?Solution:Accordingtothesimplexlapwinding,theparallelcurrentpathsaequaltothepolepairp,namely,a=p=3;AccordingtoEq.1-20,whenarmaturecurrentI1=10A,theinducedtorqueis(Nm);WhenarmaturecurrentI2=15A,theinducedtorqueis(Nm).Example1-5:

Adcgeneratorhasthesimplexlapwinding,thepolepairp=3,thetotalconductornumberN=780,theperpoleflux=1.310-2Wb,itsratedpowerPN=17kW,ratedvoltageUN=230V,ratedspeednN=1500r/min.Calculatedtheratedcurrentandtheinducedvoltage?

Solution:

TheratedcurrentisIN=PN/UN=171000/230=73.91(A);Thearmaturewindingissimplexlapwinding,theparallelcurrentpathsaequaltothepolepairp,namely,a=p=3;whenthespeednN=1500r/min,theinducedvoltageis

(V).1.5EquivalentcircuitofDCmachine

SeparatelyexcitedDCmachineShuntDCmachineSeriesDCmachineCompoundedDCmachineDCgenerator1.SeparatelyexcitedDCgenerator2.ShuntDCgenerator3.SeriesDCgenerator4.CumulativelyCompoundedDCgenerator

long-shuntconnectionshort-shuntconnectionDCMotor1.SeparatelyexcitedDCgenerator2.ShuntDCMotor3.SeriesDCMotor4.CumulativelyCompoundedDCMotor

long-shuntconnectionshort-shuntconnection1.6PowerFlowandLosses

TheLossesCopperlossesBrushlossesCore(iron)lossesMechanicallossesStraylosses1.CopperLosses(I2RLoss)2.BrushLossesArmaturewinding:Fieldwinding:

VBDisusuallyassumedtobeabouta2Vconstantoveralargerangeofarmaturecurrents.3.CoreLossesHysteresisandEddyCurrentLoss4.MechanicalLossesFrictionandwindageloss5.StrayLossesLossesthatcannotbeplacedinpreviouscategoriesandusuallybetakenbyconventiontobe1%offullload.ThePower-FlowDiagramforDCMachinesDCGeneratorEffciency：StraylossesMechanicallossesCorelossesI2Rloss转换功率(电磁功率)DCMotorThePower-FlowDiagramforDCMachinesEffciency：I2RlossesCorelossesMechanicallossesStrayloss转换功率(电磁功率)TorqueequationDCgenerator:DCmotor:

1.7OperationcharacteristicsofDCGeneratorThefollowingcharacteristiccurvesofaDCgeneratorwillbeconsidered.(1)No-loadcharacteristic,ormagnetizationcurve;n=constant(2)Regulationcharacteristic;Uandn=constant(3)Terminalcharacteristic,orexternalcurve;n=constantAsimplifiedequivalentcircuit1.7.1TheoperationcharacteristicsofaseparatelyexcitedDCgenerator

1.ThemagnetizationcurveThemagnetizationcurveofaferromagneticmaterialThemagnetizationcurveofadcmachineexpressedasaplotofEAversusIFforafixedspeedwo.NOTE:Mostmachinesaredesignedtooperatenearthesaturationpointonthemagnetizationcurve(atthekneeofthecurve膝点).ThisimpliesthatafairlylargeincreaseinfieldcurrentisoftennecessarytogetasmallincreaseinEAwhenoperationisnearfullload.2.TheterminalcharacteristicofaseparatelyexcitedDCgeneratorTheterminalcharacteristicofaseparatelyexcitedgeneratoristhusaplotofUversusIaforaconstantspeedn.

ByKirchhoff’svoltagelaw,theterminalvoltageis

3.TheregulationcharacteristicofaseparatelyexcitedDCgeneratorTheregulationcharacteristicofaseparatelyexcitedgeneratoristhusaplotofIf

versusIaforaconstantspeednandaconstantterminalvoltageU.

4.VoltagecontrolforaseparatelyexcitedDCgenerator1)Changethespeedofrotation.Ifnincrease,thenwillincrease,sowillincreasetoo.2)ChangethefieldcurrentIf.IfRfisdecreased,thenthefieldcurrentincreases.Therefore,thefluxinthemachineincreases.Asthefluxrises,mustraisetoo,soincrease.Inmanyapplications,thespeedrangeoftheprimemoverisquitelimited,sotheterminalvoltageismostcommonlycontrolledchangingbythefieldcurrent.

1.7.2TheoperationcharacteristicsofashuntDCgenerator

1、Thevoltagebuildupinashuntdcgenerator

Possiblecausesforthevoltagetofailtobuildupduringstarting(Howcanthevoltagebuildup?)ResidualmagneticfluxDirectionrotationgeneratevoltageproducesafluxincreasetheresidualflux.FieldresistanceshouldbelessthanthecriticalresistanceVoltageBuildupinashuntgenerator

Dependsonthepresenceofaresidualfluxinthepolesφres.Whengeneratorstartstoturn,φrescausesavoltageEA=KφresnEA.CausesacurrenttoflowinthefieldcoilIF,andthiscurrentproducesamagnetomotiveforceinthepoleswhichincreasetheflux.Φ↑,EA↑,VT↑,IF↑,thesehappencircularlyuntilthevoltagebuildup.n1n2n3n1>n2

>n3R3>R2

>R1

>R02.TheterminalcharacteristicofashuntDCgenerator

TheterminalcharacteristicofashuntdcgeneratoristhusaplotofUversusIaforaconstantspeedn.SameanddifferentbehaviortothatofaseparatelyexcitedDCGeneratorSame:IA↑,VT=EA-IARA↓,thusadecreasecharacteristicDifferent:VF=VT↓,IF↓,φ↓,EA↓，afurtherdecreasehappens.

3.TheregulationcharacteristicofashuntdcgeneratorTheregulationcurveofashuntdcgeneratoristhesameasthatoftheseparatelyexciteddcgenerator,becausethevoltagedropproducedbythefieldcurrentisverysmalland,incomparisonwiththevoltagedropcausedbytheloadcurrent,canbeneglected.4.Voltagecontrolforashuntdcgenerator

Aswiththeseparatelyexcitedgenerator,therearetwowaystocontrolthevoltageofashuntdcgenerator.(1).Changetheshaftspeednofthegenerator.(2).Changethefieldresistorofthegenerator,thuschangingthefieldcurrent.

Example1-6:

Ashuntdcgenerator,itsratedpowerPN=9kW,ratedvoltageUN=115V,ratedspeednN=1450r/min,armatureresistanceRa=0.15Ω,whenthegeneratorturningatratedoperationstate,thetotalresistanceofthefieldcircuitRfN=33Ω,thecorelossis410W,themechanicallossis101W,thestraylossistakenby0.5percentofratedpower.Calculatethefollowing:(1)theinducedtorqueofthegenerator?(2)Theefficiencyofthegeneratorturningatratedoperationstate?Solution:

(1)theratedcurrentofthemachineisIN=PN/UN=9000/115=78.26(A)TheratedfieldcurrentisIf=UN/RfN=115/33=3.48(A)Thearmaturecurrentis

Ia=IN+If=78.26+3.48=81.74(A)

Theelectromagneticpoweris

Pe=PN+pcuf+pcua=9000+115×3.48+81.742×0.15=10402.4(W)TheinducedtorqueisTe=Pe/Ω=10402.4×60/(2×3.14×1450)=68.54(N.m)(2)theefficiencyofthemachineis

ηN=PN/(Pe+pFe+p+pad)

=9000/(10402.4+410+101+0.005×9000)=82.13%解法2：

(1)theratedcurrentofthemachineisIN=PN/UN=9000/115=78.26(A)TheratedfieldcurrentisIf=UN/RfN=115/33=3.48(A)Thearmaturecurrentis

Ia=IN+If=78.26+3.48=81.74(A)

theinducedvoltageis

Ea=U+IaRa=115+81.740.15=127.26(V)Theelectromagneticpoweris

Pe=EaIa=127.26×81.742=10402.31(W)TheinducedtorqueisTe=Pe/Ω=10402.4×60/(2×3.14×1450)=68.54(N.m)(2)theefficiencyofthemachineis

ηN=PN/(Pe+pFe+p+pad)

=9000/(10402.4+410+101+0.005×9000)=82.13%解法3：

(1)theratedcurrentofthemachineisIN=PN/UN=9000/115=78.26(A)TheratedfieldcurrentisIf=UN/RfN=115/33=3.48(A)Thearmaturecurrentis

Ia=IN+If=78.26+3.48=81.74(A)Theinducedvoltageis

Ea=UN+IaRa=115+81.740.15=127.26(V)

Ea=Cen=127.26(V)

Ce=Ea/n=127.26/1450=0.08777CT=9.55Ce=9.550.08777=0.8382TheinducedtorqueisTe=CTIa=0.8382×81.74=68.52(N.m)(2)theefficiencyofthemachineis

ηN=PN/(Pe+pFe+p+pad)

=9000/(10402.4+410+101+0.005×9000)=82.13%1.7.3TheoperationcharacteristicsofthecompoundeddcGenerator1.Theterminalcharacteristicofashuntdcgenerator2.Voltagecontrolforacumulativelycompoundeddcgenerator

Therearetwowaystocontrolthevoltageofashuntdcgenerator.(1).Changetheshaftspeednofthegenerator.(2).Changethefieldresistorofthegenerator,thuschangingthefieldcurrent.

1.8OperationcharacteristicsofdcMotor

(1)Speedcharacteristiccurve—n=f(Ia);

If=constant,U=constantandthereisnoexternalresistanceinthearmaturecircuit.(2)Torquecharacteristiccurve—Te

=f(Ia)

If=constant,U=constantandthereisnoexternalresistanceinthearmaturecircuit.(3)Efficiencycharacteristiccurve—η=f(Ia);

If=constant,U=constantandthereisnoexternalresistanceinthearmaturecircuit.(4)Terminalcharacteristiccurve—

n

=f(Te);If=constantandU=constant.1.8.1Operationcharacteristicsofaseparatelyexciteddcmotorandashuntdcmotor

1.Thespeedcharacteristiccurve

Theidealno-loadspeed

theslope

2.Theelectromagnetictorquecharacteristiccurve3.Theefficiencycharacteristiccurve4.TheterminalcharacteristiccurveTherealno-loadspeed

(a)noarmaturereaction(b)witharmaturereaction

theratedspeedregulationnN%

5.Theman-madeterminalcharacteristiccurveofashuntdcmotor(1)ExternalresistanceRSisaddedinthearmaturecircuit

(2)TheterminalvoltageUisnotkeeptheratedvalue

(3)ThefieldcurrentIfisnotkeeptheratedvalue

Example1-7:Ashuntdcmotor,itsratedvoltageUN=220V,ratedarmaturecurrentIaN=75A,ratedspeednN=1000r/min,thetotalresistanceofthearmaturecircuitRa=0.26Ω,whenthemotorturnsatratedoperationstate,thetotalresistanceofthefieldcircuitRfN=91Ω,thecorelossis600W,themechanicallossis1989W.Calculatethefollowing:(1)theoutputtorqueofthemotorturningatratedoperationstat