Electric Machinery 电机学 Chapter1-DC machine

Chapter1DCMachinesBriefContent 1.1Introductiontodcmachines 1.2Armaturewindings 1.3Magneticfieldsofdcmachines 1.4Inducedvoltageandelectromagnetictorque 1.5Equivalentcircuitofadcmachine 1.6Powerflowandlossesindcmachine 1.7Operationcharacteristicsofdcgenerator 1.8Operationcharacteristicsofdcmotors 1.9Speedcontrolofshuntdcmotor 1.10Startingofdcmotor 1.11Brakingofdcmotor 1.12Commutation1.1.1TheConstructionofDCMachinesDCMachine(Armaturecore)(Armaturewinding)(Brushes)(Brushes)(Commutator)(Shaft)FieldpoleFieldwindingThecross-sectionofadcmachine(interpole)(Fieldpole)(York)(Armaturecore)(Armaturewinding)(Frame)FieldwindingSheetofrotor StatorandRotor Airgapwhichisseparatingstatorandrotor Stationarypart:Frame,FieldPoleand Brushes Rotatingpart:Armaturecore，Winding ShaftandCommutator DCMachines Thearmaturewindingisplacedintherotorslotandconnectedtorotatingcommutatorwhichrectifiestheinducedvoltage Thebrusheswhichareconnectedtothearmaturewinding,rideoncommutator1.1.2OperationPrincipleofDCMachines(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:theoutputelectricalpower：2、Ratedcurrent：A3、Ratedvoltage：V4、Ratedspeed：r/min5、Ratedexcitationcurrent：A6、Ratedexcitationvoltage：V8、Polenumber：polepairnumber1.1.4Ratingsofdcmachines Example1-1 Adcgenerator,itsratedpowerPN=10kW,ratedvoltageUN=230V,ratedspeednN=2850r/min,ratedefficiencyN=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,ratedefficiencyN=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）LapwindingWavewinding Elementsofalapwindingandawavewindingwithtwoturnsareshown.WindingpitchofalapandawavewindingLapwindingWavewinding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),commutatorpitch(yc),thefirstpitch(orcoilpitch)(y1)andthesecondpitch(y2). Thedistancebetweenthebeginningsoftwoconsecutiveturnsiscalledthewindingpitch(y). Thedistancebetweenthebeginningofoneturntotheendofthesameturniscalledthefirstpitch(orcoilpitch)(y1). Thelengthofthestepnecessarytofollowthroughfromtheendofoneturntothebeginningofthenextfollowingturnarecalledthesecondpitch(y2). Thedistancebetweenthetwocommutatorbarsconnectingtothetwoendsofanelementwindingiscalledthecommutatorpitch(yc). y=y1y2(lapwinding) y=y1+y2(wavewinding) y=yc(lapandwavewinding) Thefirstpitch(coilpitch,y1)oflapandwavewindingsmustbeequalorapproximatelyequaltothepolepitch(=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)1.2.1SimplexlapwindingFora4-polemachinewithfull-pitchprogressivesimplexlapwindinghavingthesamenumberofwindingelements,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=y1y=4-1=32.Windingelementsconnection:3.Developedwindingdiagram: Developedwindingconnectionwith4-polesisshowninbelow. theupperandlowerlayersareshownsidebyside.Theupperlayerisrepresentedbysolidlineandthelowerlayerisrepresentedbydottedline. theupperlayeroftheelement1isconnectedtocommutatorbar1;thelowerlayerofelement1isconnectedtotheupperlayerofelement2andcommutatorbar2,andsoforth.Thelowerlayerofthelastelement16isthenconnectedwiththeupperlayerofelement1andcommutatorbar1,andthewindingisclosed.4.Placingmagneticpolesandbrushes: ThemagneticpolesareplacedevenlyonthestatorwithNandSalternately,andthepolewidthisusuallyequalto0.75.theaxisbetweentwoadjacentNandSpolesiscalledneutralaxisorquadrature-axis. Thebrushesarepositionedaroundthecommutatorinawaythattheyareconnectedwiththeconductorslyingatthemiddlepointsofthetwomagneticpoles(NandS). thetwoconductorsofcoil1,5,9,13arelyingatthemiddlepointsofNandSpolesandcoil1,5,9,13areshortedbybrushA1,B1,A2andB2respectively.Theemfinducedintheconductorsofcoil1,5,9,13issosmallthatthecirculatingcurrentflowingthroughthebrushesisnegligible.Ingeneral,lapwindingshaveequalnumberofbrushesandpoles.5.Instantaneouscircuitdiagram:6.Parallelbranchesofwindings2a=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=(K1)/p=(151)/2=7. AccordingtoEq.1-6,y1==Q/2p=15/4=3. AccordingtoEq.1-4,y2=yy1=73=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,wavewindingshaveequalnumberofbrushesandpoles.4.Parallelbranchesofwindings2a=2(simplexwavewinding)1.3MagneticfieldsofDCmachinesNoloadoperationLoadedoperationArmaturereaction1.3.1Magneticfieldinno-loadcondition wecanseethatthelengthoftheairgapbetweenthepoleandthearmatureisnotuniform.Theairgaplengthislargerunderthepoleshoethanthoseunderotherpartsofthepole.Sothefluxdensityintheairgapbetweenpoleshoeandthearmatureissmallerthanthatoftheairgapbetweenpolefaceandarmature. thefluxdensitycurveofaDCmachineatno-loadisaflat-topshapedcurve.aflat-toppedcurve1.3.2Magneticfieldinloadedcondition1.MMFofarmaturewindingsToillustratethearmaturewindingMMF,itisassumedthatonlyarmaturewindingscarrycurrent. Fieldcurves,i.e.,thefluxdensitydistributionBaxasafunctionofdistancex,aredeterminedbythemmfFaxcurveandthelengthoftheair-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.BothfieldwindingsandarmaturewindingscarrycurrentandArmaturereaction. (1)Quadrature-axisarmaturereaction Quadrature-axisarmaturemmfproducesthenon-uniformfluxdistributionwithinapole,andasaresult,theair-gapfluxdensityunderonehalfpoleisgreaterthanthatoftheotherhalfpole. Ifthereislowmagneticsaturationinthearmatureteethandinthepoleshoe,themmfsofthefieldandarmaturewindingscanbeconsideredseparately.Thearmaturefluxdistributionisthenastraightlineunderthepoleandasaddle-shapedcurveintheinterpolarspace.Thefluxdistributioncurveisflat-toppedproducedbythefieldmmfalone. Sincethesaturationofironislow,thearmaturefluxandtheaxisofabscissaaresymmetrical.Thatmeansthemagnitudeoftheair-gapflux,whichisproportionaltotheareaofthefluxdensitycurve,remainsthesameunderloadasthatofno-load. Ifthearmatureteethandpoleshoesaresaturated,thearealyingabovecurveb0betweencurvebandcurveb0willbesmallerthanthatoflyingbelowcurveb0. Asaresultofarmaturereaction,theresultantair-gapfluxunderloadwillbelessthanthatofno-loadandtheneutralaxiswillshiftdegreetotheleft/right. (2)DemagnetizingeffectofarmaturesIngeneral,fluxcanbeweakenedundertwoconditions:1)brushesofgeneratorsareplacedinthedirectionofrotation.2)brushesofmotorsaredisplacedintheoppositedirectionofrotation.Contrarily,fluxcanbestrengthenedby1)brushesofgeneratorsaredisplacedintheoppositedirectionofrotationand2)brushesofmotorsaredisplacedinthedirectionofrotation.1.4InducedvoltageandElectromagnetic(Induced)TorqueVoltagegeneratedfromDCmachinesisthesameastheDCvoltagebetweentwobrushes,i.e.,thetotalvoltageofaparallelcircuit.1、theaveragevoltageeavinducedinconductorsBavistheaveragedensityperpole,T;eavistheaveragevoltageofoneconductor,V;listheeffectivelengthoftheconductor,m;visthemechanicalspeedoftheconductorcuttingthefield,m/s,andv=2pn/60,nistherotationspeedofthearmature,r/min.2、TheaveragevoltageEabetweentwobrushesCeisthevoltageconstantwhichdependsupontheconstructionparametersofDCmachines,Nisthetotalnumberofturnsinseriesbetweenarmatureterminals;nistherotationspeedofthearmature,r/min. Ingeneral,thevoltageofallrealDCmachinesdependsonthesamefactors: (a)Theperpolefluxinthemachine; (b)Thespeed(n)ofthemachine’srotor; (c)TheconstantCewithrespecttotheconstructionofDCmachines. Ifthesaturationofironislow,theperpolefluxcanbeexpressedKfIf,whereKfisaconstantandIfistheexcitationcurrent.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)Theperpolefluxinthemachine;(b)Thearmature(orrotor)currentIa;(c)TheconstantCTwithrespecttotheconstructionoftheDCmachine. Ifthesaturationofironislow,theperpolefluxcanbeexpressedasKfIf,whereKfisaconstantandIfistheexcitationcurrent. Example1-3: Adcmotorhasthesimplexlapwinding,thepolepairp=3,thetotalconductornumberN=398,theperpoleflux=2.110-2Wb,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=2.110-2Wb,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=1.310-2Wb,itsratedpowerPN=17kW,ratedvoltageUN=230V,ratedspeednN=1500r/min.Calculatedtheratedcurrentandtheinducedvoltage? Solution: TheratedcurrentisIN=PN/UN=171000/230=73.91(A); Thearmaturewindingissimplexlapwinding,theparallelcurrentpathsaequaltothepolepairp,namely,a=p=3; whenthespeednN=1500r/min,theinducedvoltageis(V).1.5EquivalentcircuitofDCmachineSeparatelyexcitedDCmachineShuntDCmachineSeriesDCmachineCompoundedDCmachineDCgenerator 1.SeparatelyexcitedDCgenerator 2.ShuntDCgenerator 3.SeriesDCgenerator 4.CumulativelyCompoundedDCgenerator long-shuntconnection short-shuntconnectionDCMotor 1.SeparatelyexcitedDCgenerator 2.ShuntDCMotor 3.SeriesDCMotor 4.CumulativelyCompoundedDCMotor long-shuntconnection short-shuntconnection1.6PowerFlowandLosses TheLosses Copperlosses Brushlosses Core(iron)losses Mechanicallosses Straylosses1.CopperLosses(I2RLoss)2.BrushLossesArmaturewinding:Fieldwinding: VBDisusuallyassumedtobeabouta2Vconstantoveralargerangeofarmaturecurrents.3.CoreLossesHysteresisandEddyCurrentLoss4.MechanicalLossesFrictionandwindageloss5.StrayLossesLossesthatcannotbeplacedinpreviouscategoriesandusuallybetakenbyconventiontobe1%offullload.ThePower-FlowDiagramforDCMachinesDCGeneratorEffciency：DCMotorThePower-FlowDiagramforDCMachinesEffciency：Torqueequation DCgenerator: DCmotor:1.7OperationcharacteristicsofDCGeneratorThefollowingcharacteristiccurvesofaDCgeneratorwillbeconsidered. (1)No-loadcharacteristic,ormagnetizationcurve;n=constant (2)Regulationcharacteristic;Uandn=constant (3)Terminalcharacteristic,orexternalcurve;n=constantAsimplifiedequivalentcircuit1.7.1TheoperationcharacteristicsofaseparatelyexcitedDCgenerator1.ThemagnetizationcurveThemagnetizationcurveofaferromagneticmaterialThemagnetizationcurveofadcmachineexpressedasaplotofEAversusIFforafixedspeedwo.NOTE:Mostmachinesaredesignedtooperatenearthesaturationpointonthemagnetizationcurve(atthekneeofthecurve膝点).ThisimpliesthatafairlylargeincreaseinfieldcurrentisoftennecessarytogetasmallincreaseinEAwhenoperationisnearfullload.2.TheterminalcharacteristicofaseparatelyexcitedDCgenerator TheterminalcharacteristicofaseparatelyexcitedgeneratoristhusaplotofUversusIaforaconstantspeedn. ByKirchhoff’svoltagelaw,theterminalvoltageis3.TheregulationcharacteristicofaseparatelyexcitedDCgenerator TheregulationcharacteristicofaseparatelyexcitedgeneratoristhusaplotofIfversusIaforaconstantspeednandaconstantterminalvoltageU.4.VoltagecontrolforaseparatelyexcitedDCgenerator 1)Changethespeedofrotation.Ifnincrease,thenwillincrease,sowillincreasetoo. 2)ChangethefieldcurrentIf.IfRfisdecreased,thenthefieldcurrentincreases.Therefore,thefluxinthemachineincreases.Asthefluxrises,mustraisetoo,soincrease. Inmanyapplications,thespeedrangeoftheprimemoverisquitelimited,sotheterminalvoltageismostcommonlycontrolledchangingbythefieldcurrent.1.7.2TheoperationcharacteristicsofashuntDCgenerator1、ThevoltagebuildupinashuntdcgeneratorPossiblecausesforthevoltagetofailtobuildupduringstarting(Howcanthevoltagebuildup?) Residualmagneticflux Directionrotationgeneratevoltageproducesafluxincreasetheresidualflux. FieldresistanceshouldbelessthanthecriticalresistanceVoltageBuildupinashuntgeneratorDependsonthepresenceofaresidualfluxinthepolesφres.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.Theregulationcharacteristicofashuntdcgenerator Theregulationcurveofashuntdcgeneratoristhesameasthatoftheseparatelyexciteddcgenerator,becausethevoltagedropproducedbythefieldcurrentisverysmalland,incomparisonwiththevoltagedropcausedbytheloadcurrent,canbeneglected.4.VoltagecontrolforashuntdcgeneratorAswiththeseparatelyexcitedgenerator,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)ThearmaturecurrentisIa=IN+If=78.26+3.48=81.74(A)TheelectromagneticpowerisPe=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)theefficiencyofthemachineisηN=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)ThearmaturecurrentisIa=IN+If=78.26+3.48=81.74(A)theinducedvoltageisEa=U+IaRa=115+81.740.15=127.26(V)TheelectromagneticpowerisPe=EaIa=127.26×81.742=10402.31(W)TheinducedtorqueisTe=Pe/Ω=10402.4×60/(2×3.14×1450)=68.54(N.m) (2)theefficiencyofthemachineisηN=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)ThearmaturecurrentisIa=IN+If=78.26+3.48=81.74(A)TheinducedvoltageisEa=UN+IaRa=115+81.740.15=127.26(V)Ea=Cen=127.26(V)Ce=Ea/n=127.26/1450=0.08777CT=9.55Ce=9.550.08777=0.8382TheinducedtorqueisTe=CTIa=0.8382×81.74=68.52(N.m) (2)theefficiencyofthemachineisηN=PN/(Pe+pFe+p+pad)=9000/(10402.4+410+101+0.005×9000)=82.13%1.7.3TheoperationcharacteristicsofthecompoundeddcGenerator1.Theterminalcharacteristicofashuntdcgenerator2.VoltagecontrolforacumulativelycompoundeddcgeneratorTherearetwowaystocontrolthevoltageofashuntdcgenerator. (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.ThespeedcharacteristiccurveTheidealno-loadspeedtheslope 2.Theelectromagnetictorquecharacteristiccurve 3.Theefficiencycharacteristiccurve 4.TheterminalcharacteristiccurveTherealno-loadspeed(a)noarmaturereaction(b)witharmaturereactiontheratedspeedregulationnN%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)theoutputtorqueofthemotorturningatratedoperationstate? (2)theratedefficiencyofthemotor? Solution: (1)thefieldcurrentisIf=UN/RfN=220/91=2.42(A)Th