外文翻译--直流电机地介绍.doc

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1、IntroductiontoD.C.MachinesD.C.machinesarecharacterizedbytheirversatility.Bymeansofvariouscombinationsofshunt-,series-,andseparatelyexcitedfieldwindingstheycanbedesignedtodisplayawidevarietyofvolt-ampereorspeed-torquecharacteristicsforbothdynamicandsteadystateoperation.Because

2、oftheeasewithwhichtheycanbecontrolled,systemsofD.C.machinesareoftenusedinapplicationsrequiringawiderangeofmotorspeedsorprecisecontrolofmotoroutput.TheessentialfeaturesofaD.C.machineareshownschematically.Thestatorhassalientpolesandisexcitedbyoneormorefieldcoils.Theair-gapfluxd

3、istributioncreatedbythefieldwindingissymmetricalaboutthecenterlineofthefieldpoles.Thisiscalledthefieldaxisordirectaxis.Asweknow,theA.C.voltagegeneratedineachrotatingarmaturecoilisconvertedtoD.C.intheexternalarmatureterminalsbymeansofarotatingcommutatorandstationarybrushestowh

4、ichthearmatureleadsareconnected.Thecommutator-brushcombinationformsamechanicalrectifier,resultinginaD.C.armaturevoltageaswellasanarmaturem.m.f.Wavethenis90electricaldegreesfromtheaxisofthefieldpoles,i.e.inthequadratureaxis.Intheschematicrepresentationthebrushesareshowninquadr

5、atureaxisbecausethisisthepositionofthecoilstowhichtheyareconnected.Thearmaturem.m.f.Wavethenisalongthebrushaxisasshown.(Thegeometricalpositionofthebrushesinanactualmachineisapproximately90electricaldegreesfromtheirpositionintheschematicdiagrambecauseoftheshapeoftheendconnecti

6、onstothecommutator.)Themagnetictorqueandthespeedvoltageappearingatthebrushesareindependentofthespatialwaveformofthefluxdistribution;forconvenienceweshallcontinuetoassumeasinusoidalflux-densitywaveintheairgap.Thetorquecanthenbefoundfromthemagneticfieldviewpoint.13Thetorquecanb

7、eexpressedintermsoftheinteractionofthedirect-axisair-gapfluxperpoleandspace-fundamentalcomponentofthearmaturem.m.f.wave.Withthebrushesinthequadratureaxistheanglebetweenthesefieldsis90electricaldegrees,anditssineequalsunity.Forapolemachine（1-1）Inwhichtheminussigngasbeendropped

8、becausethepositivedirectionofthetorquecanbedeterminedfromphysicalrea