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ID:28017422
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时间:2018-12-07
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1、GeneratorandElectricalEquipmentsGeneratorIntroductionElectricgeneratorsconvertmechanicalenergytoelectricalenergy,whichismoreeasilytransmittedtoremotelylocatedpointsofapplication.Thefirstlargeelectricgeneratingsystemsuseddirect-current(dc)generators,mainl
2、ybecausedirectcurrentwasbetterunderstoodthanalternatingcurrent(ac).However,dcgeneratorsarelimitedtogeneratingpoweratrelativelylowvoltages,largelyduetoproblemsattheircommutates.Aspowernetworksdeveloped,higherandhighervoltageswererequiredtotransmitlargeblo
3、cksofpoweroverlongerandlongerdistances.Electrictransformerscaneasilychangethenormallylowvoltagegeneratedtothehighvoltagesneededforefficientpowertransmission,andofcourse,transformersonlyworkonalternatingcurrent.Acgenerators,oralternatorsastheyarecommonlyc
4、alled,aresomuchsimplermechanically,somuchmoreefficient,andrequiresomuchlessmaintenancethandcmachinesthatalllargegeneratingplantsoutputalternatingcurrenttoday.Althoughdetransmissionlinescantransportextremelylargeblocksofpowerveryefficientlyoverlongdistanc
5、es,thepowerisalwaysgeneratedasalternatingcurrent,transformedtothevoltagerequired,rectifiedandtransmittedasdirectcurrent,andtheninvertedbacktoalternatingcurrentatthepointofapplication.MechanicalEnergyThemechanicalenergyfordrivingthegeneratormustbederivedf
6、romasourcewithenoughreliabilityandcapacitytomakeiteconomicallyfeasibletodevelopandtransmittheenergyelectricallytothepointofuse.Asmallwatersupplyrunningonlyduringexceptionallywetyearsorlocatedatagreatdistancefromelectricalconsumerswouldprobablynotbesuitab
7、le.Mechanicalenergysourceswhichcannotbemoved,suchashydraulicturbinesorevenwindmachines,musthavethecostoftransportingtheenergyproduced(amongotherfactors)takenintoaccountwhenoverallcostsarecalculated.Steam-turbinepowerplants,however,canbelocatednearacoalse
8、am,lumbermill,orareliablesourceofcoolingwatertosaveontransportationcosts.Somemechanicalpowermaybeobtainedfromsourcesmoreeasilylocatednearthepointofutilization.Gasturbinesandreciprocatinggasordieselenginesfallintothiscatego
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