电气工程及其自动化外文翻译

1、BriefIntroductiontoTheElectricPowerSystemPart1MinimumelectricpowersystemAminimumelectricpowersystemisshowninFig.1-1,thesystemconsistsofanenergysource,aprimemover,agenerator,andaload.EnergysourceFig-1-1ThemifilmumelectricpowersystemTheenergysourcemaybecoal,gas,oroilburnedinafurnacetoheatwaterandgener

2、atesteaminaboiler;itmaybefissionablematerialwhich,inanuclearreactor,willheatwatertoproducesteam;itmaybewaterinapondatanelevationabovethegeneratingstation;oritmaybeoilorgasburnedinaninternalcombustionengine.Theprimemovermaybeasteam-driventurbine,ahydraulicturbineorwaterwheel,oraninternalcombustioneng

3、ine.Eachoneoftheseprimemovershastheabilitytoconvertenergyintheformofheat,fallingwater,orfuelintorotationofashaft,whichinturnwilldrivethegenerator.Theelectricalloadonthegeneratormaybelights,motors,heaters,orotherdevices,aloneorincombination.Probablytheloadwillvaryfromminutetominuteasdifferentdemandso

4、ccur.Thecontrolsystemfunctions(are)tokeepthespeedofthemachinessubstantiallyconstantandthevoltagewithinprescribedlimits,eventhoughtheloadmaychange.Tomeettheseloadconditions,itisnecessaryforfuelinputtochange,fortheprimemoverinputtovary,andfortorqueontheshaftfromtheprimemovertochangeinorderthatthegener

5、atormaybekeptatconstantspeed.Inaddition,thefieldcurrenttothegeneratormustbeadjustedtomaintainconstantoutputvoltage.Thecontrolsystemmayincludeamanstationedinthepowerplantwhowatchesasetofmetersonthegeneratoroutputterminalsandmakesthenecessaryadjustmentsmanually.Inamodernstation,thecontrolsystemisaserv

6、omechanismthatsensesgenerator-outputconditionsandautomaticallymakesthenecessarychangesinenergyinputandfieldcurrenttoholdtheelectricaloutputwithincertainspecifications.Part2MoreComplicatedSystemsInmostsituationstheloadisnotdirectlyconnectedtothegeneratorterminals.Morecommonlytheloadissomedistancefrom

7、thegenerator,requiringapowerlineconnectingthem.Itisdesirabletokeeptheelectricpowersupplyattheloadwithinspecifications.However,thecontrolsarenearthegenerator,whichmaybeinanotherbuilding,perhapsseveralmilesaway.Ifthedistancefromthegeneratortotheloadisconsiderable,itmaybedesirabletoinstalltransformersa

8、tthegeneratorandattheloadend,andtotransmitthepoweroverahigh-voltageline(Fig.1-2).Forthesamepower,thehigher-voltagelinecarrieslesscurrent,haslowerlossesforthesamewiresize,andprovidesmorestablevoltage.Fl善.1-2Ageneratorconnectedthroughtransformersandahigh-voltagelineioadistantloadInsomecasesanoverheadl

9、inemaybeunacceptable.Insteaditmaybeadvantageoustouseanundergroundcable.Withthepowersystemstalkedabove,thepowersupplytotheloadmustbeinterruptedif,foranyreason,anycomponentofthesystemmustbemovedfromserviceformaintenanceorrepair.Additionalsystemloadmayrequiremorepowerthanthegeneratorcansupply.Anotherge

10、neratorwithitsassociatedtransformersandhigh-voltagelinemightbeadded.Itcanbeshownthattherearesomeadvantagesinmakingtiesbetweenthegenerators(1)andattheendofthehigh-voltagelines(2and3),asshowninFig.1-3.Thissystemwilloperatesatisfactorilyaslongasnotroubledevelopsornoequipmentneedstobetakenoutofservice.F

11、ig.1-3Asystemwithparalleloperationofthegenerators1-1*一rofthetran$formersandofthetransmissionlinesTheabovesystemmaybevastlyimprovedbytheintroductionofcircuitbreakers,whichmaybeopenedandclosedasneeded.Circuitbreakersaddedtothesystem,Fig.1-4,permitselectedpieceofequipmenttoswitchoutofservicewithoutdist

12、urbingtheremainderofsystem.Withthisarrangementanyelementofthesystemmaybedeenergizedformaintenanceorrepairbyoperationofcircuitbreakers.Low-voitageHigh-voltairebusLow-voltagebusFtg«1-4AsystemwithnecessarycircuitbreakersOfcourse,ifanypieceofequipmentistakenoutofservice,thenthetotalloadmustbecarrie

13、dbytheremainingequipment.Attentionmustbegiventoavoidoverloadsduringsuchcircumstances.Ifpossible,outagesofequipmentarescheduledattimeswhenloadrequirementsarebelownormal.Fig.1-5showsasysteminwhichthreegeneratorsandthreeloadsaretiedtogetherbythreetransmissionlines.Nocircuitbreakersareshowninthisdiagram

14、,althoughmanywouldberequiredinsuchasystem.Fir«1-STtiirccigc：mtorssupplyIng;ttire®ondisiBtgti-voltage'ton1ln<±sPart 3 TypicalSystemLayoutThegenerators,lines,andotherequipmentwhichformanelectricsystemarearrangeddependingonthemannerinwhichloadgrowsintheareaandmayberearrangedfromti

15、metotime.However,therearecertainplansintowhichaparticularsystemdesignmaybeclassified.Threetypesare川ustrated:theradialsystem,theloopsystem,andthenetworksystem.Alloftheseareshownwithoutthenecessarycircuitbreakers.Ineachofthesesystems,asinglegeneratorservesfourloads.TheradialsystemisshowninFig.1-6.Here

16、thelinesforma“tree”spreadingfromthegenerator.Openinganylineresultsininterruptionofpowertooneormoreoftheloads.fig-1AradialpowersystemsupplyingseveralloadsTheloopsystemisillustratedinFig.1-7.Withthisarrangementallloadsmaybeservedeventhoughonelinesectionisremovedfromservice.Insomeinstancesduringnormalo

17、peration,theloopmaybeopenatsomepoint,suchasA.Incasealinesectionistobetakenout,theloopisfirstclosedatAandthenthelinesectionremoved.Inthismannernoserviceinterruptionsoccur.Fig.1-7AlooparrangementuflinesfarsupplyingseveralloadsFig.1-8showsthesameloadsbeingservedbyanetwork.Withthisarrangementeachloadhas

18、twoormorecircuitsoverwhichitisfed.Fig.1-8Anetworkofline9forsupplyingseveralloadsDistributioncircuitsarecommonlydesignedsothattheymaybeclassifiedasradialorloopcircuits.Thehigh-voltagetransmissionlinesofmostpowersystemsarearrangedasnetwork.Theinterconnectionofmajorpowersystemresultsinnetworksmadeupbym

19、anylinesections.Part 4 AuxiliaryEquipmentCircuitbreakersarenecessarytodeenergizeequipmenteitherfornormaloperationorontheoccurrenceofshortcircuits.Circuitbreakersmustbedesignedtocarrynormal-loadcurrentscontinuously,towithstandtheextremelyhighcurrentsthatoccurduringfaults,andtoseparatecontactsandclear

20、acircuitinthepresenceoffault.Circuitbreakersareratedintermsoftheseduties.Whenacircuitbreakeropenstodeenergizeapieceofequipment,onesideofthecircuitbreakerusuallyremainsenergized,asitisconnectedtooperatingequipment.Sinceitissometimesnecessarytoworkonthecircuitbreakeritself,itisalsonecessarytohavemeans

21、bywhichthecircuitbreakermaybecompletelydisconnectedfromotherenergizedequipment.Forthispurposedisconnectswitchesareplacedinserieswiththecircuitbreakers.Byopeningthesedisconnectors,thecircuitbreakermaybecompletelydeenergized,permittingworktobecarriedoninsafety.Variousinstrumentsarenecessarytomonitorth

22、eoperationoftheelectricpowersystem.Usuallyeachgenerator,eachtransformerbank,andeachlinehasitsownsetofinstruments,frequentlyconsistingofvoltmeters,ammeters,wattmeters,andvarmeters.Whenafaultoccursonasystem,conditionsonthesystemundergoasuddenchange.Voltagesusuallydropandcurrentsincrease.Thesechangesar

23、emostnoticeableintheimmediatevicinityoffault.On-lineanalogcomputers,commonlycalledrelays,monitorthesechangesofconditions,makeadeterminationofwhichbreakershouldbeopenedtoclearthefault,andenergizethetripcircuitsofthoseappropriatebreakers.Withmodernequipment,therelayactionandbreakeropeningcausesremoval

24、offaultwithinthreeorfourcyclesafteritsinitiation.Theinstrumentsthatshowcircuitconditionsandtherelaysthatprotectthecircuitsarenotmounteddirectlyonthepowerlinesbutareplacedonswitchboardsinacontrolhouse.Instrumenttransformersareinstalledonthehigh-voltageequipment,bymeansofwhichitispossibletopassontothe

25、metersandrelaysrepresentativesamplesoftheconditionsontheoperatingequipment.Theprimaryofapotentialtransformerisconnecteddirectlytothehigh-voltageequipment.Thesecondaryprovidesfortheinstrumentsandrelaysavoltagewhichisaconstantfractionofvoltageontheoperatingequipmentandisinphasewithit;similarly,acurren

26、ttransformerisconnectedwithitsprimaryinthehigh-currentcircuit.Thesecondarywindingprovidesacurrentthatisaknownfractionofthepower-equipmentcurrentandisinphasewithit.Bushingpotentialdevicesandcapacitorpotentialdevicesservethesamepurposeaspotentialtransformersbutusuallywithlessaccuracyinregardtoratioand

27、phaseangle.中文翻译：电力系统的简介第一部分：最小电力系统一个最小电力系统如图1-1所示，系统包含动力源，原动机，发电机和负载。动力源可能是火炉中的煤，燃气或石油，加热锅炉中的水而产生蒸汽。它也可能是可裂变的材料，如原子核反应堆，加热水而产生蒸汽；也可能是在高海拔发电站上水池的水；或者是石油或燃气在内燃机中的燃烧。原动机可能是汽轮机，水轮机，水车，或内燃机。这些原动机中的一种都有能力把其他形式的能量转化为热能，势能，或使轴转动的能量，进而驱动发电机工作。发电机上的电负载可能是灯，电动机，加热器或是其他设备的个体或组合。负载可能在每一分钟内都会产生不相同的需要。控制系统的功能是保持机器

28、的速度是个稳定值和保持电压在规定的范围内变化，即使负载可能发生变化。要满足这些负载的条件，需要燃料输入的变化，需要原动机输入的变化，这是为了改变发电机中原动机轴的转矩保持恒定。止匕外,发电机的励磁电流必须加以调整，以保持恒定电压输出。该控制系统可能包括一个驻扎在电厂里的人，他看管着发电机输出终端的一整套仪表和有时进行必要的手动调整。在一个现代化的电站里，控制系统用来感应发电机输出条件，在能源输入中自动进行必要的改变和磁场电流在规定的范围内保持电力输出的一个伺服机构。第二部分：更复杂的系统在大多数情况下负载不是直接与发电机终端连接在一起的。更常见的是负载与发电机有一段距离，需要电源线把它们连接起

29、来。理想情况下是在规定的范围内对负载保持电能补给，进而控制附近的发电机。发电机可能在另一幢大楼里，也可能有几英里远。如果发电机到负载的距离是合理的，理想的情况是在发电机和负载的端部都安装变压器，通过高压线路传送电能（如图1-2）。对于相同的电能输送，更高的电压线路会流过更小的电流，对于同样尺寸的电线则降低更多的损耗，提供更稳定的电压。在某些情况下架空线可能是不合适的。相反，使用地下电缆可能会更有利。上面谈到的电力系统，不管任何原因，负载的电能补给必须被中断，供电中系统的任何元件必须被维护或者被移除。其他系统的负载所需的电能可能比发电机需要的电能更大。另外，与发电机相关的变压器和高压线路可能被增

30、加。由上可以说明连接发电机（1）和高压线路末端（2和3）是有一些优势的，如图1-3所示。这个系统只要没有任何故障或没有需求的设备在供电中被移除时，其运行将令人满意。上面的系统通过引进断路器将有很大的改善，这需要使用断路器的开通和关断功能。增加断路器的系统，如图1-4,允许选择某台设备在供电中被关断，不会影响剩余的系统设备。采用这种布局的系统可能通过断路器的操作对其进行不带电的维护或维修。当然，任何一台设备从供电中被移除，总负载必须在剩余设备中被运行。在上述情况下必须注意的是避免过载。如果可能，在低于正常值的负载需求，设备的停电是要有时间计划的。如图1-5所示，通过三条输电线路，系统的三个发电机和三个负载是捆绑在一起的。在此图中没有断路器，然而在很多时候这样的系统是被需要的。第三部分：典型的系统布局电力系统中发电机，线路和其他设备根据该地区负载的增加和变化不时的被重新排放。然而，真正的计划归类是一个特别的系统设计。三种系统类型说明：放射性系统，循环系统和网络系统。所有这些都说明不需要断路器。这些系统中的每一个都是由一个发电机来供给四个负