电力系统的演化.docx
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电力系统的演化.docx
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电力系统的演化
中文2188字
EVOLUTIONOFELECTRICPOWERSYSTEMS
Thecommercialuseofelectricitybeganinthelate1870swhenarclampswereusedforlighthouseilluminationandstreetlighting.
Thefirstcompleteelectricpowersystem(comprisingagenerator,cable,fuse,meter,andloads)wasbuiltbyThomasEdison-thehistoricPearlStreetStationinNewYorkCitywhichbeganoperationinSeptember1882.Thiswasadcsystemconsistingofasteam-engine-drivendcgeneratorsupplyingpowerto59customerswithinanarearoughly1.5kminradios.Theload,whichconsistedentirelyofincandescentlamps,wassuppliedat110Vthroughanundergroundcablesystem.Withinafewyearssimilarsystemswereinoperationinmostlargecitiesthroughouttheworld.WiththedevelopmentofmotorsbyFrankSpraguein1884,motorloadswereaddedtosuchsystems.Thiswasthebeginningofwhatwoulddevelopintooneofthelargestindustriesintheworld.
Inspiteoftheinitialwidespreaduseofdcsystems,theywerealmostcompletelysupersededbyacsystems.By1886,thelimitationsofdcsystemswerebecomingincreasinglyapparent.Theycoulddeliverpoweronlyashortdistancefromthegenerators.Tokeeptransmissionpowerlosers(RI2)andvoltagedropstoacceptablelevels,voltagelevelshadtobehighforlong-distancepowertransmission.Suchhighvoltageswerenotacceptableforgenerationandconsumptionofpower;therefore,aconvenientmeansforvoltagetransformationbecameanecessity.
ThedevelopmentofthetransformationandactransmissionbyL.GaulardandJ.D.GibbsofParis,France,ledtoacelectricpowersystems.GeorgeWestinghousesecuredrightstothesedevelopmentsintheUnitedStates.In1886,WilliamStanley,anassociateofWestinghouse,developedandtestedacommerciallypracticaltransformerandacdistributionsystemfor150lampsatGreatBarrington,Massachusetts.In1889,thefirstactransmissionlineinNorthAmericawasputintooperationinOregonbetweenWillametteFallsandPortland.Itwasasingle-phaselinetransmittingpowerat4,000Voveradistanceof21km.
WiththedevelopmentofpolyphasesystemsbyNikolasTesla,theacsystembecameevenmoreattractive.By1888,Teslaheldseveralpatentsonacmotors,generators,transformers,andtransmissionsystems.Westinghouseboughtthepatentstotheseearlyinventions,andtheyformedthebasisofthepresent-dayacsystems.
Inthe1890s,therewasconsiderablecontroversyoverwhethertheelectricutilityindustryshouldbestandardizedondcorac.TherewerepassionateargumentsbetweenEdison,whoadvocateddc,andWestinghouse,whofavoredac.Bytheturnofthecentury,theacsystemhadwonoutoverthedcsystemforthefollowingreasons;
●Voltagelevelscanbeeasilytransformedinacsystems,thusprovidingtheflexibilityforuseofdifferentvoltagesforgeneration,transmission,andconsumption.
●ACgeneratorsaremuchsimplerthandcgenerators.
●ACmotorsaremuchsimplerandcheaperthandcmotors.
Thefirstthree-phaselineinNorthAmericawentintooperationin1893-a2,300V,12kmlineinsouthernCalifornia.Aroundthistime,acwaschosenatNiagaraFallsbecausedcwasnotpracticalfortransmittingpowertoBuffalo,about30kmaway.Thisdecisionendedtheacversusdccontroversyandestablishedvictoryfortheacsystem.
Intheearlyperiodofacpowertransmission,frequencywasnotstandardized.Manydifferentfrequencieswereinuse:
25,50,60,125,and133Hz.Thisposedaproblemforinterconnection.Eventually60HzwasadoptedasstandardinNorthAmerica,althoughmanyothercountriesuse50Hz.
Theincreasingneedfortransmittinglargeramountsofpoweroverlongerdistancescreatedanincentivetouseprogressivelyhighervoltagelevels.Theearlyacsystemsused12,44,and60kV(RMSline-to-line).Thisroseto165kVin1922,220kVin1923,287kVin1935,330kVin1953,and765kVwasintroducedintheUnitedStatesin1969.
Toavoidtheproliferationofanunlimitednumberofvoltages,theindustryhasstandardizedvoltagelevels.Thestandardsare115,138,161,and230kVforthehighvoltage(HV)class,and345,500and765kVfortheextra-highvoltage(EHV)class.
Withthedevelopmentofmercuryarcvalvesintheearly1950s,highvoltagedc(HVDC)transmissionsystemsbecameeconomicalinspecialsituations.TheHVDCtransmissionisattractivefortransmissionoflargeblocksofpoweroverlongdistances.Thecross-overpointbeyondwhichdctransmissionmaybecomeacompetitivetoactransmissionisaround500kVforaround500kmforoverheadlinesand50kmforundergroundorsubmarinecables.HDVCtransmissionalsoprovidesanasynchronouslinkbetweensystemswhereacinterconnectionwouldbeimpracticalbecauseofsystemstabilityconsiderationsorbecausenominalfrequenciesofthesystemsaredifferent.ThefirstmoderncommercialapplicationofHVDCtransmissionoccurredin1954whentheSwedishmainlandandtheislandofGotlandwereinterconnectedbya96kmsubmarinecable.
Withtheadventofthyristorvalveconverters,HVDCtransmissionbecameevenmoreattractive.ThefirstapplicationofanHVDCsystemusingthyristorvalueswasatEelRiverin1972-aback-to-backschemeprovidinganasynchronoustiebetweenthepowersystemsofQuebecandNewBrunswick.Withthecostandsizeofconversionequipmentdecreasinganditsreliabilityincreasing,therehasbeenasteadyincreaseintheuseofHVDCtransmission.
Interconnectionofneighboringutilitiesusuallyleadstoimprovedsecurityresultsfromthemutualemergencyassistancethattheutilitiescanprovide.Improvedeconomyresultsfromtheneedforlessgeneratingreservecapacityineachsystem.Inaddition,theinterconnectionpermitstheutilitiestomakeeconomytransfersandthustakeadvantageofthemosteconomicalsourcesofpower.Thesebenefitshavebeenrecognizedfromthebeginningandinterconnectionscontinuetogrow.AlmostalltheutilitiesintheUnitedStatesandCanadaarenowpartofoneinterconnectedsystemofenormouscomplexity.Thedesignofsuchasystemanditssecureoperationareindeedchallengingproblems.
STRUCTUREOFTHEPOWERSYSTEM
Electricpowersystemvariesinsizeandstructuralcomponents.However,theyallhavethesamebasiccharacteristics:
●Arecomprisedofthree-phaseacsystemsoperatingessentiallyatconstantvoltage.Generationandtransmissionfacilitiesusethree-phaseequipment.Industrialloadsareinvariablythree-phase;single-phaseresidentialandcommercialloadsaredistributedequallyamongthephasessoastoeffectivelyformabalancedthree-phasesystem.
●Usesynchronousmachinesforelectricity.Primemoversconventtheprimarysourcesofenergy(fossil,nuclear,andhydraulic)tomechanicalenergythatis,inturn,convertedtoelectricalenergybysynchronousgenerators.
●Transmitpoweroversignificantdistancestoconsumersspreadoverawidearea.Thisrequiresatransmissionsystemcomprisingsubsystemsoperatingatdifferentvoltagelevels.
Electricpowerisproducedatgeneratingstations(GS)andtransmittedtoconsumersthroughacomplexnetworkofindividualcomponents,includingtransmissionlines,transformers,andswitchingdevices.
Itiscommonpracticetoclassifythetransmissionnetworkintothefollowingsubsystems:
1.Transmissionsystem
2.Subtransmissionsystem
3.Distributionsystem
Thetransmissionsysteminterconnectsallmajorgeneratingstationsandmainloadcantersinthesystem.Itformsthebackboneoftheintegratedpowersystemandoperatesatthehighestvoltagelevels(typically,230kVandabove).Thegeneratorvoltageareusuallyintherangeof11to35kV.Thesearesteppeduptothetransmissionvoltagelevels,andpoweristransmittedtotransmissionsubstationswherethevoltagearesteppeddowntothesubtransmissionlevel(typically,69kVto138kV).Thegenerationandtransmissionsubsystemsareoftenreferredtoasthebulkpowersystem.
Thesubtransmissionsystemtransmitspowerinsmallerquantitiesfromthetransmissionsubstationstothedistributionsubstations.Largeindustrialcustomersarecommonlysupplieddirectlyfromthesubstransmissionsystem.Insomesystems,thereisnocleardemarcationbetweensubstransmissionandtransmissioncircuits.Asthesystemexpandsandhighervoltagelevelsbecomenecessaryfortransmission,theoldertransmissionlinesareoftenrelegatedtosubtransmissionfunction.
Thedistributionsystemrepresentsthefinalstageinthetransferofpowertotheindividualcustomers.Theprimarydistributionvoltageistypicallybetween4.0kVand34.5kV.Smallindustrialcustomersaresuppliedbyprimaryfeedersatthisvoltagelevel.Thesecondarydistributionfeedersaresupplyresidentialandcommercialcustomersat120/240V.
翻译:
电力系统的演化
商业用电始于19世纪70年代后期,弧灯用于灯塔照明和街道照明。
第一个完整的电力系统(由发电机、电缆、熔丝、电表和负荷组成)是由ThomasEdison在纽约城的PearlStreetStation建成并与1882年9月投入运行,这是一个由蒸汽发动机驱动供给1.5公里内59个用户组成的直流输电系统。
负荷是包括白炽灯在内的110V供电的电缆系统。
几年之内类似系统在运行在全世界大多数大城市中。
随着1884年弗兰克电机的发展,电机负载计入电力系统系统。
这是电力发展为世界最大产业之一的开始。
尽管最初广泛使用直流系统,(但后来)几乎完全交流系统所取代。
到1886年,直流系统的局限性日益突现,只能在很短的距离内从发电机向外送电。
为了保持功率损耗和电压降落在可接受水平,需提高电压水平以保证远距离输电。
发电机和用电设备不能承受较高电压电能,因此,方便转换电压成为一种必要。
由于L.Gaulard和法国巴黎的J.D.Gibbs开发了变压器和交流输电技术,由此产生了交流电力系统。
GeorgeWestinghouse获得了这些新权利在美国应用的权利。
在1886年,西屋的助手WilliamStanley开发和试验了商业实用的变压器和在GreatBrrington,Massachusetts的由150个电灯组成的交流配电系统。
在1889年,第一个交流输电线路在北美Oregon的WillametteFalls和Portland之间投运。
这是一个单相线传输电能为4000V输送距离超过21公里的电力系统。
随着NikolasTesla多相系统的建立和发展,交流系统变得更加有吸引力。
到1888年,Tesla持有关于交流电动机、发电机、变压器和输电系统的若干专利。
Westinghouse购买了这些早期发明专利,这些发明奠定了当今交流电力系统的基础。
在19世纪90年代,关于电力工业应采用直流还是交流作为标准的相当大的争论。
在主张直流的Edison和偏好交流的Westinghouse之间发生过激烈的辩论。
到世纪末,交流系统战胜了直流系统,原因如下:
在交流系统中容易变压,因此可以灵活地使用不同电压等级的发电机,变压器和用电设备。
交流发电机比直流发电机简单得多。
交流电动机比直流发电机更简单,更便宜。
第一个三相12公里2300V输电线路在于1893年在北美Californi
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