专业外语教学资料专业英语第6单元

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1、6DCMotorAndinductionMotor6.1TYPESOFMOTORSThetypesofcommerciallyavailableDCmotorsbasicallyfallintofourcategories:（Dpennanent-magnetDCmotor,©series-wound（串励）DCmotors,©shunt-wound（并励）DCmotors,and©compound-wound（复励）DCmotors.Eachofthesemotorshasdifferentcharacteristicsduetoitsbasiccir

2、cuitarrangementandphysicalproperties.6.1.1Permanent-magnetDCmotorsThepennanent-magnetDCmotor,showninFig.6丄isconstructedinthesamemannerasitsDCgeneratorcounterpart.Thepermanent-magnetmotorisusedforlow-torqueapplications.Whenthistypeofmotorisused,theDCpowersupplyisconnecteddirectlyt

3、othearmatureconductorsthroughthebrush/commutatorassembly.Themagneticfieldisproducedbypennanentmagnetsmountedonthestator.Therotorofpermanentmagnetisawoundarmature.Thistypeofmotorordinarilyuseseitheralnico（铝鎳钻合金）orceramic（陶瓷）permanentmagnetsratherthanfieldcoils.Thealnicomagnetsareu

4、sedwithhigh-horsepowerapplications.Ceramicmagnetsareusedforlow-horsepowershow-speedmotors.Ceramicmagnetsarehighlyresistanttodemagnetization,yettheyarerelativelylowinmagnetic・fluxlevel.Themagnetsareusuallymountedinthemotorfameandthenmagnetizedpriortotheinsertionofthearmature.Thepe

5、rmanent-magnetmotorhasseveraladvantagesoverconventionaltypeofDCmotors.Oneadvantageisreducedoperationalcost.Thespeedcharacteristicsofthepermanent-magnetmotoraresimilartothoseoftheshunt-woundDCmotor.Thedirectionofrotationsofapermanent-magnetmotorcanbereversedbyreversingthetwopowerl

6、ines.(3)Pictorialdiagram(b)SchematicdiagramFig.6.1Permanent-magnetDCmotor6.1.1Series-woundDCmotorsThemannerinwhichtheannatureandfieldcircuitsofaDCmotorsareconnecteddeterminesitsbasiccharacteristics.EachofthetypeofDCmotorsaresimilarinconstructiontothetypeofDCgeneratorthatcorrespon

7、dstoit.Theonlydifference,inmostcases,isthatthegeneratoractsasavoltagesourcewhilethemotorfunctionsasamechanicalpowerconversiondevice.Theseries-woundmotor,showninFig.6.2,hasthearmatureandfieldcircuitsconnectedinaseriesarrangement.ThereisonlyonepathforcurrenttoflowfromtheDCvoltageso

8、urce.Therefore,thefieldiswoundofrelative