外文翻译---直流发电机

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1、附录外文资料翻译A1.1原文DCGENENRATORS1.INTRODUCTIONForallpracticalpurposes,thedirect-currentgeneratorisonlyusedforspecialapplicationsandlocaldcpowergeneration.Thislimitationisduetothecommutatorrequiredtorectifytheinternalgeneratedacvoltage,therebymakinglargescaledcpowergeneratorsnotfeasibl

2、e.Consequently,allelectricalenergyproducedcommerciallyisgeneratedanddistributedintheformofthree-phaseacpower.Theuseofsolidstateconvertersnowadaysmakesconversiontodceconomical.However,theoperatingcharacteristicsofdcgeneratorsarestillimportant,becausemostconceptscanbeappliedtoallot

3、hermachines.2.FIELDWINDINGCONNECTIONSThegeneralarrangementofbrushesandfieldwindingforafour-polemachineisasshowninFig.1.Thefourbrushesrideonthecommutator.ThepositivebrusherareconnectedtoterminalA1whilethenegativebrushesareconnectedtoterminalA2ofthemachine.Asindicatedinthesketch,th

4、ebrushesarepositionedapproximatelymidwayunderthepoles.TheymakecontactwithcoilsthathavelittleornoEMFinducedinthem,sincetheirsidesaresituatedbetweenpoles.Figure1Sketchoffour-poledcmatchineThefourexcitationorfieldpolesareusuallyjoinedinseriesandtheirendsbroughtouttoterminalsmarkedF1

5、andF2.Theyareconnectedsuchthattheyproducenorthandsouthpolesalternately.Thetypeofdcgeneratorischaracterizedbythemannerinwhichthefieldexcitationisprovided.Ingeneral,themethodemployedtoconnectthefieldandarmaturewindingsfallsintothefollowinggroups(seeFig.2):Figure2Fieldconnectionsfor

6、dcgenerators(a)separatelyexcitedgenerator(b)self-excited,shuntgenerator(c)seriesgenerator(d)compoundgenerator;short-shuntconnection(e)compoundgenerator,long-shuntconnection.Theshuntfieldcontainsmanyturnsofrelativelyfinewireandcarriesacomparativelysmallcurrent,onlyafewpercentofrat

7、edcurrent.Theseriesfieldwinding,ontheotherhand,hasfewturnsofheavywiresinceitisinserieswiththearmatureandthereforecarriestheloadcurrent.Beforediscussingthedcgeneratorterminalcharacteristics,letusexaminetherelationshipbetweenthegeneratedvoltageandexcitationcurrentofageneratoronnolo

8、ad.ThegeneratedEMFisproportionaltobothth