外文翻译--直流电机的介绍

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

2、ation.Becauseoftheeasewithwhichtheycanbecontrolled,systemsofD.C.machinesareoftenusedinapplicationsrequiringawiderangeofmotorspeedsorprecisecontrolofmotoroutput.TheessentialfeaturesofaD.C.machineareshownschematically.Thestatorhassalientpolesandisexcitedbyoneormore

3、fieldcoils.Theair-gapfluxdistributioncreatedbythefieldwindingissymmetricalaboutthecenterlineofthefieldpoles.Thisiscalledthefieldaxisordirectaxis.Asweknow,theA.C.voltagegeneratedineachrotatingarmaturecoilisconvertedtoD.C.intheexternalarmatureterminalsbymeansofarot

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

5、ntheschematicrepresentationthebrushesareshowninquadratureaxisbecausethisisthepositionofthecoilstowhichtheyareconnected.Thearmaturem.m.f.Wavethenisalongthebrushaxisasshown.(Thegeometricalpositionofthebrushesinanactualmachineisapproximately90electricaldegreesfromth

6、eirpositionintheschematicdiagrambecauseoftheshapeoftheendconnectionstothecommutator.)Themagnetictorqueandthespeedvoltageappearingatthebrushesareindependentofthespatialwaveformofthefluxdistribution;forconvenienceweshallcontinuetoassumeasinusoidalflux-densitywavein

7、theairgap.Thetorquecanthenbefoundfromthemagneticfieldviewpoint.13Thetorquecanbeexpressedintermsoftheinteractionofthedirect-axisair-gapfluxperpoleandspace-fundamentalcomponentofthearmaturem.m.f.wave.Withthebrushesinthequadratureaxistheanglebetweenthesefieldsis90el

8、ectricaldegrees,anditssineequalsunity.Forapolemachine（1-1）Inwhichtheminussigngasbeendroppedbecausethepositivedirectionofthetorquecanbedeterminedfromphysicalrea