induction motor.pdf

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1、www.PDHcenter.comPDHCourseE176www.PDHonline.orgINDUCTIONMOTORTHEORYJerryBednarczyk,PECourseContentINTRODUCTIONTheACinductionmotoriswellsuitedtoapplicationsrequiringconstantspeedoperation.Ingeneral,theinductionmotorischeaperandeasiertomaintaincomparedtootheralternatives.Theinductionmo

2、torismadeupofthestator,orstationarywindings,andtherotor.Thestatorconsistsofaseriesofwirewindingsofverylowresistancepermanentlyattachedtothemotorframe.Asavoltageandacurrentisappliedtothestatorwindingterminals,amagneticfieldisdevelopedinthewindings.Bythewaythestatorwindingsarearranged,

3、themagneticfieldappearstosynchronouslyrotateelectricallyaroundtheinsideofthemotorhousing.Therotoriscomprisedofanumberofthinbars,usuallyaluminum,mountedinalaminatedcylinder.Thebarsarearrangedhorizontallyandalmostparalleltotherotorshaft.Attheendsoftherotor,thebarsareconnectedtogetherwi

4、tha“shortingring.”Therotorandstatorareseparatedbyanairgapwhichallowsfreerotationoftherotor.TypicalInductionMotorRotorsThemagneticfieldgeneratedinthestatorinducesanEMFintherotorbars.Inturn,acurrentisproducedintherotorbarsandshortingringandanothermagneticfieldisinducedintherotorwithano

5、ppositepolarityofthatinthestator.Themagneticfield,revolvinginthestator,willthenproducesthetorquewhichwill“pull”onthefieldintherotorandestablishrotorrotation.Inthedesignoftheinductionmotor,operationalcharacteristicscanbedeterminedthroughaseriesofcalculations.Performingthesecalculation

6、scanhelptheengineerPage1of13www.PDHcenter.comPDHCourseE176www.PDHonline.orgprovideamotorthatisbestsuitedtoaparticularapplication.Thispaperwilldemonstratetheirapplication.Page2of13www.PDHcenter.comPDHCourseE176www.PDHonline.orgSYNCHRONOUSSPEEDThespeedwithwhichthestatormagneticfieldrot

7、ates,whichwilldeterminethespeedoftherotor,iscalledtheSynchronousSpeed(SS).TheSSisafunctionofthefrequencyofthepowersourceandthenumberofpoles(polepairs)inthemotor.TherelationshiptocalculatetheSSofaninductionmotoris:1SS=(120Xf)/PWhere:SS=SynchronousSpeed(RPM)f=frequency(cycles/second)=6

8、0P=numberofp