section 6ppt课件

.,Chapter6ElectricPowerSystems,.,Section2ComponentsofPowerSystems,Text,NewWordsandExpressions,Exercises,End,TranslationofNegativeSentences,.,Section2ComponentsofPowerSystems,Modernpowersystemsareusuallylarge-scale,geographicallydistributed,andwithhundredstothousandsofgeneratorsoperatinginparallelandsynchronously.Theymayvaryinsizeandstructurefromonetoanother,buttheyallhavethesamebasiccharacteristics:（1）Arecomprisedofthree-phaseACsystemsoperatingessentiallyatconstantvoltage.Generationandtransmissionfacilitiesusethree-phaseequipment.Industrialloadsareinvariably,.,Section2ComponentsofPowerSystems,three-phase;single-phaseresidentialandcommercialloadsaredistributedequallyamongthephasessoastoeffectivelyformabalancedthree-phasesystem.（2）Usesynchronousmachinesforgenerationofelectricity.Primemoversconverttheprimaryenergy(fossil,nuclear,andhydraulic)tomechanicalenergythatis,inturn,convertedtoelectricalenergybysynchronousgenerators.,.,Section2ComponentsofPowerSystems,（3）Transmitpoweroversignificantdistancestoconsumersspreadoverawidearea.Thisrequiresatransmissionsystemcomprisingsubsystemsoperatingatdifferentvoltagelevels.ThebasicelementsofamodernpowersysteminU.S.A.areshowninFig.6-1.Electricpowerisproducedatgeneratingstations(GS)andtransmittedtoconsumersthroughacomplexnetworkofindividualcomponents,includingtransmissionlines,transformers,andswitchingdevices.Itiscommonpracticetoclassifythe,.,Section2ComponentsofPowerSystems,transmissionnetworkintothefollowingsubsystems:Transmissionsystem;Subtransmissionsystem;Distributionsystem.,.,Section2ComponentsofPowerSystems,Fig.6-1Basicelementsofapowersystem,.,Section2ComponentsofPowerSystems,Thetransmissionsysteminterconnectsallmajorgeneratingstationsandmainloadcentersinthesystem.Itformsthebackboneoftheintegratedpowersystemandoperatesatthehighestvoltagelevels(typically,230kVandaboveinU.S.A.).Thegeneratorvoltagesareusuallyintherangeof11to35kV.Thesearesteppeduptothetransmissionvoltagelevel,andpoweristransmittedtotransmissionsubstationswherethevoltagesaresteppeddowntothesubtransmissionlevel(typically,69to138kV).Thegenerationandtransmissionsubsystemsareoftenreferredtoasthe,.,Section2ComponentsofPowerSystems,bulkpowersystem.Thesubtransmissonsystemtransmitspowerinsmallquantitiesfromthetransmissionsubstationstothedistributionsubstations.Largeindustrialcustomersarecommonlysupplieddirectlyfromthesubtransmissionsystem.Insomesystems,thereisnocleardemarcationbetweensubtransmissionandtransmissioncircuits.Asthesystemexpandsandhighervoltagelevelsbecomenecessaryfortransmission,theoldertransmissionlinesareoftenrelegatedtosubtransmissionfunction.,.,Section2ComponentsofPowerSystems,Thedistributionsystemrepresentsthefinalstageinthetransferofpowertotheindividualcustomers.Theprimarydistributionvoltageistypicallybetween4.0kVand34.5kV.Smallindustrialcustomersaresuppliedbyprimaryfeedersatthisvoltagelevel.Thesecondarydistributionfeederssupplyresidentialandcommercialcustomersat120/240V.,.,Section2ComponentsofPowerSystems,Smallgeneratingplantslocatedneartheloadarealsoconnectedtothesubtransmissionordistributionsystemdirectly.Interconnectionstoneighboringpowersystemsareusuallyformedatthetransmissionsystemlevel.Theoverallsystemthusconsistsofmultiplegeneratingsourcesandseverallayersoftransmissionnetworks.Thisprovidesahighdegreeofstructuralredundancythatenablesthesystemtowithstandunusualcontingencieswithoutservicedisruptiontothecustomers.,Return,.,NewWordsandExpressions,inparallel并联地synchronouslyad.同步地facilityn.容易，方便灵活，熟练（便利）条件（常用复数）设备，装置，工具，器材primaryenergy一次能源fossiln.化石，石块hydraulica.水力学的，水压的，液压的，液力的mechanicalenergy机械能,.,NewWordsandExpressions,switchingdevice开关装置，开关设备subtransmissionn.二次输电subtransmissionsystem分支输电系统，二次输电系统distributionsystem配电系统substationn.变电所，变电站，分站，分所feedern.馈线，馈电电路redundancyn.多余，冗余contingencyn.意外事故，偶然事故,Return,.,TranslationofNegativeSentences,四、意义上的肯定英语中有的否定词与其他词连用形成一个固定结构，这种结构在形式上是否定的，但意义上是肯定的，常见的有nothinglike（没有什么比得上），cannottoo（越越好），no/not/nothing+more+than（不过），no/not/nothing+less+than（多达）等。（1）Theimportanceoftheprojectcanhardlybeexaggerated.这项工程的重要性怎么说也不过分。,.,TranslationofNegativeSentences,四、意义上的肯定（2）Itisimpossibletooverestimatethevalueoftheinvention.这项发明的价值无论怎样估计也不会太高。（3）Pesticidescancausealotofharm,soyoucanneverbetoocarefulwhenusingpesticides.杀虫剂会造成很大危害，所以当使用杀虫剂时应特别小心。,.,TranslationofNegativeSentences,五、含蓄否定英语里有些词或词组形式上是肯定的，但意义往往是否定的。由这类词或词组表达的否定称为含蓄否定。翻译时，一般要把否定的意义明确译出，可译成“不”、“没”、“没有”、“非”等。1.动词或动词短语引起的否定常见的有deny拒绝，否认，fail失败，lack缺乏，refuse拒绝，stop停止protectfrom,保护免受，keepfrom避免，overlook忽视，忽略，miss失败，错过等。,.,TranslationofNegativeSentences,五、含蓄否定1.动词或动词短语引起的否定(1)Theexperimentfailedofsuccess.实验没有成功。(2)Thevalueoflossinthisequationissosmallthatwecanoverlookit.在此方程中，损耗值太小，可以忽略不计。(3)Thespecificationlacksdetail.这份说明书不够详尽。,.,TranslationofNegativeSentences,五、含蓄否定2.名词引起的否定常见的有neglect忽视，absence缺乏，loss失去，exclusion排除，ignorance无知等。Afewinstrumentsareinastateofneglect.一些仪器处于无人管理状态。,.,TranslationofNegativeSentences,五、含蓄否定3.形容词或形容词短语引起的否定常见的有freefrom不受影响，ignorantof不知道，shortof缺乏，last最不，little少，few少等。(1)Theprecisioninstrumentmustbekeptfreefromdust.精密仪器必须保持无尘。(2)Thisequationisfarfrombeingcomplicated.这个方程式一点也不复杂。,.,TranslationofNegativeSentences,五、含蓄否定4.介词或介词短语引起的否定常见的有beyond超出，above超出之外，beneath不值得，beside同无关，insteadof而不是等。(1)Theproblemisbeyondthereachofmyunderstanding.这个问题我无法理解。(2)TheTheoryofRelativityworkedoutbyEinsteinisnowabovemanypeoplescomprehension.爱因斯坦提出的“相对论”，现在还有不少人理解不了,.,TranslationofNegativeSentences,五、含蓄否定5.连词及其某些短语引起的否定常见的有before在以前，尚未，but而不，wouldratherthan宁可而不愿，与其不如，ratherthan而不，tooto太不等。Neverstarttodotheexperimentbeforeyouhavecheckedthemeter.没有检查好仪表，切勿开始做试验。,Return,.,Exercises,I.Choosethebestanswerintotheblank,1.Inpowerplantsconverttheprimaryenergytomechanicalenergy,andcon-vertmechanicalenergytoelectricenergy.A.synchronousgenerators,primemoversB.primemovers,synchronousgeneratorsC.primemovers,asynchronousgeneratorsD.primemovers,primemovers,.,Exercises,I.Choosethebestanswerintotheblank,2.Thegeneratorvoltagesareusuallysteppeduptothetransmissionvoltagelevelby.A.seriescapacitorsB.parallelreactorsC.step-uptransformersD.step-downtransformers3.Residentialandcommercialcustomersaresuppliedbythesecondarydistributionfeedersat.A.120/240VB.220/380VC.110/220VD.48/110V,.,Exercises,I.Choosethebestanswerintotheblank,4.InU.S.A.,thevoltagesofthetransmissionsystemaretypically.A.345kVB.500kVC.230kVandaboveD.115kVandabove,.,Exercises,II.Answerthefollowingquestionsaccordingtothetext,1.Whatcomponentsisamodernpowersystemcomprisedof?2.Whatisthefunctionofthedistributionsystem?3.Whatisthefunctionofthetransmissionsystem?4.Whatisthefunctionofthesubtransmissionsystem?5.Whatisthecharacteristicsofamodernpowersysteminnetworkstructure?,.,Exercises,III.TranslatethefollowingintoChinese,Instabilitymayalsobeencounteredwithoutlossofsynchronism.Forexample,asystemconsistingofasynchronousgeneratorfeedinganinduc