专业外语教学资料专业英语第7单元

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1、7ElectricalMachineControlSystemsThepreviouschaptershavedealtprimarilywiththetypesandcharacteristicsofelectricalmachines・Thischapterprovidesanoverviewofseveralpowercontrolsystemswhichareusedwithelectricalmachines.7.1CONTROLSYMBOLSItisnecessarytobecomefamiliarwiththeelectricalsymbolswhicharecommonlyus

2、edwithmachinecontrolsystems.SomecommonmachinecontrolsymbolsareshowninFig.7」•Normallyclosed“NormallyNormallyopenclosedNonnallyNormallyThermalNonnallyopen•closedopen"7ContactsOOOHeldCircuitbreakerclosed0^0HeldopenDoublecircuitMaintainedLiquidlevelNormallyNonnallyopbnclosedclLdNormally-o州NormallyopenTO

3、**~orQIOOPushbuttonscolorbyX：XiletterTMagnacoilTransformer

4、^mpThrc^phascThermal总？*HEZD-MgZZR则卜gAutotr»n<^.L'FootswitchNormallyclosedTO^oroyoTime-delayAdjustablccontactAutotransfbnncrHcsistorNormallyclosedTC*~orFixedFig.7・1Commonmachinecontrolsymbols7.1MACHINECONTROLWITHSWITCHES(电机的开关控制)Animportantty

5、peofelectricalmachinecontrolistheswitch.Manytypesofswitchesareusedtocontrolelectricalmachines.Thefunctionofaswitchistoturnacircuitonoroff;however,manymorecomplexswitchfunctionscanbeperformed・7.2.1ToggleswitchesAmongthesimplesttypeofswitchesaretoggleswitches.Thesymbolsforseveralkindsoftoggleswitchesa

6、reshownFig.7.2.Noticethesymbolsthatareusedforvarioustypesoftoggleswitches(自锁开关，切换开关).(c)Doublepole,singlethrow7°^Commonor°“Hinge”point(a)Singlepole,singlethrow(b)Three-wayorsinglepole,doublethrow(d)Doublepole,doublethrow(c)Threepole,singlethrowFig•7•2ToggleswitchesO^rOOa0*06(f)Threepole,doublethrow7

7、.2.2Pushbuttonswitches(按钮开关)Pushbuttonswitchesarecommonlyusedformachinecontrol.Manymachinecontrolapplicationsusepushbuttonsasameansofstarting,stopping,orreversingamotor;Pushbuttonsaremanuallyoperatedtocloseoropenamachinecontrolcircuit・Thereareseveraltypesofpushbuttonsuseforthecontrolofmachines.Pushb

8、uttonsareusuallymountedinenclosurescalledmotorcontrolstations（电机控制箱）.Ordinarily,pushbuttonsareeitherthenormallyclosed（NC）ornormallyopen（NO）types・However,thereareafewmodifications.Anormallyclosedpushbu