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,therebymakinglargescal

2、edcpowergeneratorsnotfeasible.Consequently,allelectricalenergyproducedcommerciallyisgeneratedanddistributedintheformofthree-phaseacpower.Theuseofsolidstateconvertersnowadaysmakesconversiontodceconomical.However,theoperatingcharacteristicsofdcgenerators

3、arestillimportant,becausemostconceptscanbeappliedtoallothermachines.2.FIELDWINDINGCONNECTIONSThegeneralarrangementofbrushesandfieldwindingforafour-polemachineisasshowninFig.1.Thefourbrushesrideonthecommutator.ThepositivebrusherareconnectedtoterminalA1w

4、hilethenegativebrushesareconnectedtoterminalA2ofthemachine.Asindicatedinthesketch,thebrushesarepositionedapproximatelymidwayunderthepoles.TheymakecontactwithcoilsthathavelittleornoEMFinducedinthem,sincetheirsidesaresituatedbetweenpoles.Figure1Sketchoff

5、our-poledcmatchineThefourexcitationorfieldpolesareusuallyjoinedinseriesandtheirendsbroughtouttoterminalsmarkedF1andF2.Theyareconnectedsuchthattheyproducenorthandsouthpolesalternately.Thetypeofdcgeneratorischaracterizedbythemannerinwhichthefieldexcitati

6、onisprovided.Ingeneral,themethodemployedtoconnectthefieldandarmaturewindingsfallsintothefollowinggroups(seeFig.2):Figure2Fieldconnectionsfordcgenerators(a)separatelyexcitedgenerator(b)self-excited,shuntgenerator(c)seriesgenerator(d)compoundgenerator;sh

7、ort-shuntconnection(e)compoundgenerator,long-shuntconnection.Theshuntfieldcontainsmanyturnsofrelativelyfinewireandcarriesacomparativelysmallcurrent,onlyafewpercentofratedcurrent.Theseriesfieldwinding,ontheotherhand,hasfewturnsofheavywiresinceitisinseri

8、eswiththearmatureandthereforecarriestheloadcurrent.Beforediscussingthedcgeneratorterminalcharacteristics,letusexaminetherelationshipbetweenthegeneratedvoltageandexcitationcurrentofageneratoronnoload.ThegeneratedEMFisproportionaltobothth