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Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-0PowerPointSlidestoaccompanyElectricMachineryFourthEditionStephenJ.ChapmanChapter5InductionMotorsCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-1Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-27.1PrincipleandStructure•Characterisedby–Nosaliency–Havingastatorandarotorwinding,–Bothstatorandrotorwindingsarepoly-phase–Statorwindingisconnectedtoanacsupply–RotorwindingisshortcircuitedCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-3Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-4•Twoformsofmachinedependentonrotor–Squirrelcage•Rotorshortcircuitedontherotoritself–Slipring•Rotorhaselectricalslidingconnectionslinkingtheelectricalconnectionstothestationarystator(notthewinding)Theshortcircuit,oraddinginofextraresistance,totherotoristhenmadeexternaltothemachineCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-5Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-63PhaseStatorWindingCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-7Squirrelcagerotor.Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-8RotorShowingSingleBarsShortCircuitedby“EndRings”Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-9SimilarSquirrelCageRotortoPreviousSlideShowingBarsJustBelowtheSurfaceoftheRotorLaminationsCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-10Woundrotor.•Mostmotorsusethesquirrel-cagerotorbecauseoftherobustandmaintenance-freeconstruction.•However,large,oldermotorsuseawoundrotorwiththreephasewindingsplacedintherotorslots.•Thewindingsareconnectedinathree-wirewye.•Theendsofthewindingsareconnectedtothreesliprings.•ResistorsorpowersuppliesareconnectedtotheslipringsthroughbrushesforreductionofstartingcurrentandspeedcontrolCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-11•thethree-phasewindingsaredisplacedfromeachotherby120degreesinspace•aphasecoilproducesasinusoidaldistributedMMFwavecenteredontheaxisofthecoilCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-12•alternatingcurrentineachcoilproducesapulsatingMMFwave•MMFwavesaredisplacedby120degreesinspacefromeachother•resultantMMFwaveisrotatingalongtheairgapwithconstantpeakCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-13Rotatingmagneticfield–GraphicalmethodCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-14Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-15InducedVoltagesCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-16fordistributedwindingwithwindingfactorKw•rotoropen-circuited•rotatingfieldintheairgap–speedns•fieldinducesvoltagesinstatorandrotorwindings–samefrequencyCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-17Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-18Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-19•rotorcircuitisclosed•inducedvoltagesproducerotorcurrentsthatinteractswithairgapfieldtoproducetorque•rotorstartstorotate•relativespeeddecreases-inducedvoltagedecreases–torquebalance•Slip•frequencyofinducedrotorcurrentsCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-20•inducedrotorvoltage•speedofinducedrotorfieldwithrespecttotherotoris•andwithrespecttothestatorisCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-21Equivalentcircuit•Aninductionmotorhastwomagneticallycoupledcircuits:thestatorandtherotor.Thelatterisshort-circuited.•Thisissimilartoatransformer,whosesecondaryisrotatingandshort-circuited.Copyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-22•Themotorhasbalancedthree-phasecircuits;consequently,thesingle-phaserepresentationissufficient.•Boththestatorandrotorhavewindings,whichhaveresistanceandleakageinductance.•ThestatorandrotorwindingarerepresentedbyaresistanceandleakagereactanceconnectedinseriesCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-23•Atransformerrepresentsthemagneticcouplingbetweenthetwocircuits.•Thestatorproducesarotatingmagneticfieldthatinducesvoltageinbothwindings.–Amagnetizingreactance(Xm)andaresistanceconnectedinparallelrepresentthemagneticfieldgeneration.–Theresistance(Rc)representstheeddycurrentandhysteresislossesintheironcore•TheinducedvoltageisdependontheslipandtheturnratioCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-24•TheMMFofMotor(rotoropen-circuit)（1）AmplitudeCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.6-25（2）Rotatesp