电机学（第七版）（修订版）课件 Chapter-4-Introduction-to-Rotating-Machines

Chapter4IntroductiontoRotatingMachines7/10/2024IntroductiontoRotatingMachines14.1ElementaryConceptsRotatingmachines:voltagesareinducedinwindingsorgroupsofcoilsbyrotationofamagneticfieldpastawindingorrotationofawindingthroughthefield,orbydesigningthemagneticcircuitsothatthereluctancevarieswithrotationoftherotorSincethefluxlinkingacoilchangescyclically,atime-varyingvoltageisinducede=dl/dtAgroupsuchcoilscarryingACcurrentsisoftencalledanarmaturewinding7/10/2024IntroductiontoRotatingMachines27/10/2024IntroductiontoRotatingMachines3Statorofa100-MVAthree-phasesynchronousgeneratorunderconstruction.(GeneralElectricCompany.)Armatureofadcmotor.(BaldorElectric/ABB)InanACsynchronousmachine,thearmatureistypicallyonthestatorInaDCmachine,thearmatureislocatedontherotorDCandsynchronousmachinestypicallyhavefieldwindingscarryingDCtosetupthemainoperatingflux,usuallylocatedonthestatorforDCmachinestherotorofACsynchronousmachinesSomemachines,especiallymotors,usemagnetsinsteadoffieldwindingsInductionmachinesdonothavefields,butproducefluxsimilarlytotransformersManytypesofmachinesexist,butverysimilarphysicalprinciplesgoverntheirperformance7/10/2024IntroductiontoRotatingMachines44.2IntroductiontoACandDCmachinesTraditionalacmachinesareclassifiedassynchronousorinductionmachinesSynchronousmachines:rotorcurrentsaresupplieddirectlyfromthestationaryframe,througharotatingcontactforexampleInductionmachines:rotorcurrentsareinducedintherotorwindingsbymagneticinductionfromthestatorwindings7/10/2024IntroductiontoRotatingMachines5Fieldhasasinglepairofpoles,soitisatwo-polemachineArmatureherehasasinglecoilofNturnsFieldisexcitedthroughbrushescontactingsliprings,orbybrushlessexcitationsystemIftheair-gapfluxissinusoidalinspace,theinducedvoltageinthearmatureissinusoidalintime,asthemachinerotatesatconstantspeed7/10/2024IntroductiontoRotatingMachines6Schematicviewofasimple,two-pole,single-phasesynchronousgeneratorManymachineshavemorethantwopoles.Afour-polesynchronousmachine,whichwillrotateathalfthespeedofatwo-polemachineifthefrequencyisthesame7/10/2024IntroductiontoRotatingMachines7IdealizedfluxdistributionandwaveformofgeneratedvoltageFour-polesingle-phasesynchronousgeneratorForconvenienceinanalyzingmachineswithmorethantwopoles,defineelectricalangleandelectricalspeed,asfollows:7/10/2024IntroductiontoRotatingMachines8SubscripteindicateselectricalunitswhilemindicatesmechanicaloractualunitsThisisusefulsincetherearepoles/2completewavelengthsorcyclesinone(mechanical)revolutionInductionMachinesStatorwindingsareessentiallythesameasasynchronousmachineRotorwindingiselectricallyshort-circuitedandoftenhasnoexternalconnections,derivingitsexcitationbymagneticinductionAlsocalledasynchronousmachinesCommonconstructionforaninductionmotorusesthesquirrel-cagerotorwithnoexternalconnectionSquirrel-cageinductionmotorsarethemostcommontypeofmotorusedtoday7/10/2024IntroductiontoRotatingMachines9CagerotorhasbarsthatareshortedbyendringsInexpensivetoconstructandyetveryruggedRotorcurrentsareinducedastherotorslipspastthestatorfluxwave,whichrotatesatsynchronousspeedFluxwavesetupbytherotorcurrentsrotatesatsynchronousspeed,andinteractswiththestatorfluxtoproducetorqueThismachineisverysimilartoatransformer,butwithrotationofwindings7/10/2024IntroductiontoRotatingMachines10Cutawayviewofa460-V,7.5hpsquirrel-cageinductionmotor.DCMachinesAsimplifieddcgeneratorarmaturewinding(asinglecoilofNturns)isshownThecommutatorisacylindricalstructurewithtwosegmentsattachedtotherotor,servingasamechanicalrectifiertoconverttheacinthearmaturecoiltodcatthestationarybrushes7/10/2024IntroductiontoRotatingMachines11ElementarydcmachineDCinthefieldsetsupastationaryfluxThecommutatorcausesarmaturefluxtobefixedinspacebetweenthefieldpolesInteractionoffluxessetsuptorque7/10/2024IntroductiontoRotatingMachines12Air-gapfluxdistributionandvoltagewaveform4.3MMFofDistributedWindingsPracticalarmaturewindingsareusuallydistributed,orspreadoveranumberofslotsConsideronephaseofanacthree-phasetwo-polewinding(calledafull-pitchwindingsinceeachcoilspanspradians)FourieranalysisgivesthespacefundamentalcomponentoftheMMF,developedinAppendixB7/10/2024IntroductiontoRotatingMachines137/10/2024IntroductiontoRotatingMachines14Themmfofonephaseofadistributedtwo-pole,three-phasewindingwithfull-pitchcoils.7/10/2024IntroductiontoRotatingMachines15Thepeakvalueofthespacefundamentalisgiveninthefollowingequation,wherekwisthewindingfactorthataccountsforthedistributionofthewinding(seeAppendixBfordetails)ThefactorkwNphistheeffectivenumberofseriesturnsperphaseTypicalvaluesforkware0.85to0.90ConsiderthedcmachinewithanarmaturewindingdistributedovermanyslotsAnapproximationtothemmfisasawtoothwave7/10/2024IntroductiontoRotatingMachines16Crosssectionofatwo-poledcmachine7/10/2024IntroductiontoRotatingMachines17Currentandmmfwaveofidealizeddcmachine4.4MagneticFieldsinRotatingMachineryMachinewithauniformairgapandasinglefull-pitchN-turncoilonahighlypermeableironcore7/10/2024IntroductiontoRotatingMachines18Diagramofmachine7/10/2024IntroductiontoRotatingMachines19MMFandfielddistributionsSpacefundamentalfieldpeakvalue:4.5RotatingMMFWavesSingle-phasewindingproducesapulsatingMMFthatcanberesolvedintotwoequalrotatingwaves,rotatinginoppositedirectionsPolyphasewindingproducesarotatingMMFthathasconstantamplitudeandconstantspeedinsteadystateThefigureonthenextslideshowsagraphicalexplanationwhilethetextgivesamathematicalderivationforthethree-phasecase7/10/2024IntroductiontoRotatingMachines207/10/2024IntroductiontoRotatingMachines21Theproductionofarotatingmagneticfieldbymeansofthree-phasecurrentsFistheresultantofvectoradditionofFa+Fb+Fc4.6GeneratedVoltageFluxdensityisnearlysinuosoidalinspacePhase-afluxlinkage:7/10/2024IntroductiontoRotatingMachines22Generatedvoltage(constantfluxinnormalsteadystate):DCMachinesCommutatoractsasarectifier,givingaveragevoltage:7/10/2024IntroductiontoRotatingMachines234.7TorqueinNon-Salient-PoleMachinesTorquecanbefoundfromeith