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ID:49500974
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时间:2020-03-02
《专业外语教学资料 专业英语第5单元.doc》由会员上传分享,免费在线阅读,更多相关内容在工程资料-天天文库。
1、Part2ElectricalMachine,ControlComponentandSensorP80〜95IntroductiontoElectricalMachines5.1BRIEFHISTORYOFELETRICALMACHINESElectricalmachineryhasbeeninexistenceformanyyears・Theapplicationsofelectricalmachineshaveexpandedrapidlysincetheirfirstusemanyyearsago.Atthepresenttime,applicationscontinu
2、etoincreaseatarapidrate.ThomasEdisonisgivencreditfordevelopingtheconceptofwidespreadgenerationanddistributionofelectricalpower.Heperformeddevelopmentalworkondirect-current(DC)generatorswhichweredrivenbysteamengines・Edison'sworkwithelectricallightsandpowerproductionledthewaytothedevelopmento
3、fDCmotorsandassociatedcontrolequipment.Mostearlydiscoveriesrelatedtoelectricalmachineryoperationdealtwithdirect-currentsystems.Alternating-current(AC)powergenerationanddistributionbecamewidespreadashorttimelater.TheprimaryreasonforconvertingtoACpowerproductionanddistributionwasthattransform
4、erscouldbeusedtoincreaseACvoltagelevelsforlong・distancedistributionofelectricalpower.Thusthediscoveryoftransformers(变压器)allowedtheconversionofpowerproductionanddistributionsystemsforDCtoACsystems.Presently,almostallelectricalpowersystemsproduceanddistributethree-phasealternatingcurrent.Tran
5、sformersallowthevoltageproducedbyanACgeneratortobeincreasedwhiledecreasingthecurrentlevelbyacorrespondingamount.Thisallowslong-distancedistributionatareducedcurrentlevel,reducespowerlosses,andincreasessystemefficiency.Theuseofelectricalmotors(电机)hasincreasedforhomeappliancesfordrivingmachin
6、esandandautomatedindustrialThusmotordesignandmotorswhichwereusedandindustrialandcommercialapplicationssophisticatedequipment.Manymachinesequipmentnowrequireprecisecontrol.complexityhaschangedsinceearlyDCprimarilywithrailroadtrains.Motorcontrolmethodshavenowbecomemorecriticaltotheefficientan
7、deffectiveoperationofmachinesandequipment.Suchinnovations(新事物)asservo(伺Jj艮)controlsystemsandindustrialrobotshaveledtonewdevelopmentsinmotordesign.Ourcomplexsystemoftransportationhasalsohadanimpact(7中击)ontheuseofelectricalmachines・Automobilesandothermeans
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