論文英文翻譯

畢業(yè)設(shè)計（論文）英文文獻(xiàn)翻譯電力系統(tǒng)電力系統(tǒng)介紹隨著電力工業(yè)的增長，與用于生成和處理當(dāng)今大規(guī)模電能消費(fèi)的電力生產(chǎn)、傳輸、分配系統(tǒng)相關(guān)的經(jīng)濟(jì)、工程問題也隨之增多。這些系統(tǒng)構(gòu)成了一個完整的電力系統(tǒng)。應(yīng)該著重提到的是生成電能的工業(yè)，它與眾不同之處在于其產(chǎn)品應(yīng)按顧客要求即需即用。生成電的能源以煤、石油，或水庫和湖泊中水的形式儲存起來，以備將來所有需。但這并不會降低用戶對發(fā)電機(jī)容量的需求。顯然，對電力系統(tǒng)而言服務(wù)的連續(xù)性至關(guān)重要。沒有哪種服務(wù)能完全避免可能出現(xiàn)的失誤，而系統(tǒng)的成本明顯依賴于其穩(wěn)定性。因此，必須在穩(wěn)定性與成本之間找到平衡點(diǎn)，而最終的選擇應(yīng)是負(fù)載大小、特點(diǎn)、可能出現(xiàn)中斷的原因、用戶要求等的綜合體現(xiàn)。然而，網(wǎng)絡(luò)可靠性的增加是通過應(yīng)用一定數(shù)量的生成單元和在發(fā)電站港灣各分區(qū)間以及在國內(nèi)、國際電網(wǎng)傳輸線路中使用自動斷路器得以實(shí)現(xiàn)的。事實(shí)上大型系統(tǒng)包括眾多的發(fā)電站和由高容量傳輸線路連接的負(fù)載。這樣，在不中斷總體服務(wù)的前提下可以停止單個發(fā)電單元或一套輸電線路的運(yùn)作。當(dāng)今生成和傳輸電力最普遍的系統(tǒng)是三相系統(tǒng)。相對于其他交流系統(tǒng)而言，它具有簡便、節(jié)能的優(yōu)點(diǎn)。尤其是在特定導(dǎo)體間電壓、傳輸功率、傳輸距離和線耗的情況下，三相系統(tǒng)所需銅或鋁僅為單相系統(tǒng)的75%。三相系統(tǒng)另一個重要優(yōu)點(diǎn)是三相電機(jī)比單相電機(jī)效率更高。大規(guī)模電力生產(chǎn)的能源有：從常規(guī)燃料（煤、石油或天然氣）、城市廢料燃燒或核燃料應(yīng)用中得到的蒸汽；水；石油中的柴油動力。其他可能的能源有太陽能、風(fēng)能、潮汐能等，但沒有一種超越了試點(diǎn)發(fā)電站階段。在大型蒸汽發(fā)電站中，蒸汽中的熱能通過渦輪輪轉(zhuǎn)換為功。渦輪必須包括安裝在軸承上并封閉于汽缸中的軸或轉(zhuǎn)子。轉(zhuǎn)子由汽缸四周噴嘴噴射出的蒸汽流帶動而平衡地轉(zhuǎn)動。蒸汽流撞擊軸上的葉片。中央電站采用冷凝渦輪，即蒸汽在離開渦輪后會通過一冷凝器。冷凝器通過其導(dǎo)管中大量冷水的循環(huán)來達(dá)到冷凝的效果，從而提高蒸汽的膨脹率、后繼效率及渦輪的輸出功率。而渦輪則直接與大型發(fā)電機(jī)相連。渦輪中的蒸汽具有能動性。蒸汽進(jìn)入渦輪時壓力較高、體積較小，而離開時卻壓力較低、體積較大。蒸汽是由鍋爐中的熱水生成的。普通的鍋爐有燃燒燃料的爐膛燃燒時產(chǎn)生的熱被傳導(dǎo)至金屬爐壁來生成與爐體內(nèi)壓力相等的蒸汽。在核電站中，蒸汽的生成是在反應(yīng)堆的幫助下完成的。反應(yīng)堆中受控制的鈾或盥的裂變可提供使水激化所必需的熱量，即反應(yīng)堆代替了常規(guī)電站的蒸汽機(jī)。水電站是利用蘊(yùn)藏在消遣的能來發(fā)電的。為了將這種能轉(zhuǎn)換為功，我們使用了水輪機(jī)?，F(xiàn)代水輪機(jī)可分為兩類：脈沖式和壓力式（又稱反應(yīng)式）。前者用于重要設(shè)備，佩爾頓輪是唯一的類型；對于后者而言，弗朗西斯渦輪或其改進(jìn)型被廣泛采用。在脈沖式渦輪中，整個水頭在到達(dá)葉輪前都被轉(zhuǎn)化為動能，因?yàn)樗峭ㄟ^噴嘴提供給葉輪的；而在壓力式或反應(yīng)式渦輪中，水通過其四周一系列引導(dǎo)葉版先直接導(dǎo)入葉片再提供給葉輪（或轉(zhuǎn)子）。離開引導(dǎo)葉片的水有壓力，并且以一部分動能、一部分壓力的形式來提供能量。對于低于10,000千伏安的發(fā)電站而言柴油機(jī)是出色的原動機(jī)。其優(yōu)點(diǎn)是燃料成本低、預(yù)熱時間短以及標(biāo)準(zhǔn)損耗低。此外，其所需冷卻水量極少。柴油發(fā)電通常選擇用于滿足少量電力需求，如市政當(dāng)局、賓館及工廠等；醫(yī)院通常備有獨(dú)立的柴油發(fā)電機(jī)，以備緊急情況時使用。通過電線來傳輸電能是電力系統(tǒng)中的一個重大問題。而從下面研修目的目的架設(shè)輸電線路又是必要的：將電力從水電站輸送到可能很遠(yuǎn)的負(fù)載中心；從蒸汽站到相對較近負(fù)載中心電力的批量供應(yīng)；出于內(nèi)部連接目的將電能在緊急情況下從一系統(tǒng)轉(zhuǎn)換至另一系統(tǒng)。傳輸電壓主要由經(jīng)濟(jì)因素決定。實(shí)際上，當(dāng)距離、功率、功耗固定時，輸電線路中導(dǎo)體的重量與傳輸電壓成反比。因此，出于經(jīng)濟(jì)方面的考慮，長距離傳輸時電壓一定要高。當(dāng)然，電壓超高絕緣成本也就超高，要找到最佳電壓必須通過減小導(dǎo)體橫截面積來取得絕緣成本與經(jīng)濟(jì)節(jié)省之間的平衡。高壓傳輸通常使用配以懸掛式絕緣設(shè)備的高架結(jié)構(gòu)。稱為路標(biāo)鐵塔用于負(fù)載andbyusingautomaticbreakersfortheseparationintosectionsofthebusbarsingeneratingstationsandofthetransmissionlinesinanationalorinternationalgridsystem.Infactalargesystemcomprisesnumerousgeneratingstationsandloadsinterconnectedbyhigh-capacitytransmissionlines.Anindividualunitofgenerationorsetoftransmission‘linescanusuallyceasetofunctionwithoutinterruptingthegeneralservice.Themostusualsystemtodayforgenerationandforthegeneraltransmissionofpoweristhethree-phasesystem.Infavorofthissystemareitssimplicityanditssimplicityanditssavingwithrespecttoothera.c.system.Inparticular,foragivenvoltagebetweenconductors,withagivenpowertransmitted,withagivendistance,andwithagivelineloss,thethree-phasesystemrequiresonly75percentofthecopperoraluminiumneededinthesingle-phasesystem.Anotherimportantadvantageofthethree-phasesystemisthatthree-phasemotorsaremoreefficientthansingle-phaseones.Thesourcesofenergyofrlarge-scaleelectricitygenerationare:steamobtainedbymeansofaconventionalfuel(coal,oilornaturalgas),thecombustionofcityrefuseortheemploymentofnuclearfuel;water;dieselpowerfromoil.Thereareotherpossiblesourcesofenergysuchasdirectsolarheat,windpower,tidalpower,etc.,butnoneofthesehasyetgonebeyondthepilot-plantstage.Inlargesteampowerplants,thethermalenergystoredinsteamisconvertedintoworkbymeansofturbines.Aturbineconsistsessentiallyofashaftorrotorfixedinbearingsandenclosedinacylindricalcasing.Therotorismadetoturnsmoothlybymeansofjetsofsteamfromnozzlesaroundtheperipheryoftheturbinecylinder.Thesesteamjetsstrikebladesattachedtotheshaft.Centralpowerstationsemploycondensingturbinesinwhichthesteampassesintoacondenserafterleavingtheturbine.Condensationiseffectedbythecirculationoflargequantitiesofcoldwaterthroughthetubesofthecondenser,thusincreasingtheexpansionratioofthesteamandtheconsequentefficiencyandworkoutputoftheturbine.Theturbinesareconnecteddirectlytolargeelectricitygenerators.Inturbinestheactionofthesteamiskinetic.Thereisprogressiveexpansionofthesteamfromthehighpressureandrelativelysmallvolumeatwhichitleaves.Steamismadebyheatingwaterinaboiler.Theusualboilerhasafurnaceinwhichfuelisburned,andtheheatgivenoffduringcombustionisconductedthroughthemetalwallsoftheboilertogeneratesteamatapressurewithintheboilervessel.Innuclearplants,steamisgeneratedwiththeaidofareactorinwhichthecontrolledfissionofuraniumorplutoniumsuppliesthenecessaryheatforthevaporizationofwater.Thusthereactorrep;acesthesteamgeneratorofconventionalplants.Useismadeoftheenergypossessedbywaterinhydroelectricstations.Inordertotransformthisenergyintowork,hydraulicturbinesareused.Modernhydraulicturbinesmaybedividedintotwoclasses:impulseturbinesandpressureorreactionturbines.Oftheformer,thePeltonwheelistheonlytypeusedinimportantinstallations;ofthelatter,theFrancisturbineoroneofitsmodificationsisuniversallyemployed.Inanimpulseturbine,thewholeheadofwaterisconvertedintokineticenergybeforethewheelisreached,asthewaterissuppliedtothewheelthroughanozzle.Inthepressureorreactionturbinethewheel(orrunner)isprovidedwithvanesintowhichwaterisdirectedbymeansofaseriesofguidevanesaroundthewholeperiphery.Thewaterleavingtheseguidevanesisunderpressureandsuppliesenergypartlyinthekineticformandpartlyinthepressureform.Thedieselengineisanexcellentprimemoverforelectricitygenerationinplantbelowabout10,000KVA.Ithastheadvantageoflowfuelcost,abriefwarming-upperiodandlowstandinglosses.Moreoveritrequireslittlecoolingwater.Dieselgenerationisgenerallychosenforsmallpowerrequirementsbymunicipalities,hotelsandfactories;hospitalsoftenkeepandindependentdieselgeneratorforemergencysupply.Thetransmissionofelectricalenergybymeansoflinesisagreatprobleminelectricalpowersystems.Transmissionlinesareessentialforthreepurposes:Totransmitpowerfromahydroelectricsitetoaloadcenterperhapsaconsiderabledistanceaway;Forthebulksupplyofpowerfromsteamstationstoloadcentersarelativelyshortdistanceaway;Forinterconnectionpurposestotransferenergyfromonesystemtoanotherincaseofemergency.Thetransmissionvoltageisdeterminedlargelybyeconomicfactors.Infact,inatransmissionline,ifthedistance,thepowerandthepowerlossarefixed,thetotalweightoftheconductorvariesinverselyasthesquareofthetransmissionvoltage.Fortheeconomictransmissionofpoweroverconsiderabledistancesthevoltagemustthereforebehigh.Naturallywithhighervoltagestheinsulationcostalsorisesandtofindtheoptimumvoltagewemuststrikeabalancebetweenthiscostandthesavingthroughthereductionofthecross-sectionoftheconductors.Forhighvoltages,overhead-lineconstructionisgenerallyusedwithsuspension-typeinsulators.Steeltower,calledpylonsservetocarrytheinsulators,witheachconductorsuspendedfromthebottomofagrouporstringofinsulatorunits.Thefollowingtypesofconductorarethosemostcommonlyused:strandedcopperconductors,hollowcopperconductorsandACSR(aluminumcable,steelreinforced)conductors.Distributionincludesallthepartsoftheelectricitysystembetweenthepowersubstationssuppliedfromhigh-voltagetransmissionlinesandtheconsumer’sswitch.Electricpowerisreceivedfromsubstationsanddistributedtotheconsumersatthevoltagelevelsandwiththedegreeofcontinuitythatareacceptabletothevarioustypesofconsumer.Inlargemetropolitansystemsbothoverheadandundergrounddistributionmethodsareused.Althoughundergrounddistributionismoreexpensivethananoverheadsystem,itisvirtuallyanecessaryinheavilyurbanizedareas.Insmallertownsandinthelesscongesteddistrictsoflargecities,theentiredistributionsystemisusuallyoverhead.ElectricSystemMonitoringAmodernelectricpowersystemisanassemblyofmanycomponentseachofwhichinfluencesthebehaviorofeveryotherpart.Properfunctioningofthesystemasawholemakesitnecessarytomonitorconditionsexistionatmanydifferentpointsonthesysteminordertoassureoptimumoperation.Theconcernofthecustomersisprimarilythatthefrequencyandvoltageofthesupplyareheldwithincertainrathernarrowlimits.Sincefrequencyofthesystemisthesameeverywhere,itmaybemonitoredbyasinglefrequencymeterlocatedatanyconvenientpoint.Incontrastthevoltageofthesystemmaybequitedifferentatdifferentpoints.Consequently,itisnecessarytomakecontinuousobservationofthevoltageatcertainkeypointsonthesysteminordertoprovideacceptableservice.Efficientoperationofthesystemisobtainedbyassigningproperloadschedulestoeachofthegeneratorsonthesystem.Newerplants,althoughindividuallymoreefficient,maybelocatedatpointsonthesystemwheretheirloadingoccasionslargesystemlosses.Itisdesirabletooperatewithadivisionoftheloadbetweengeneratorssothatthetotalcostoffuelconsumedisminimized.Toprovidereliabilityofthepowersupplyintileeventofunexpectedconditions,itisdesirabletohavethetotalkilowattratingofallmachinesinoperationsomewhatgreaterthanthetotalloadpluslosses.Thisexcessofgeneration,knownasspinningreserve,isthenavailableforpickingupsuddenlyappliedcustomerloadsortopickuptheloaddroppedbyageneratorthatmustberemovedfromserviceforemergencymaintenance.InstrumentationisnecessarytopermitbillingofCustomersforenergyused.Manyinterconnectionsexistbetweendifferentpowersystems.Instrumentsmustbeprovidedatinterchangepointstopermitbillingforenergytransferredfromonesystemtoanother.Thecontinuousmonitoringofenergytransferisnecessarytoassurethatinterchangedpoweriswithinthelimitsofcontractagreements.Thecontinuousmeasurementofconditionsonmajorpiecesofequipmentisnecessarytoavoiddamageduetooverload.Asloadincreasesfrommonthtomonth,pointsatwhichadditionalcapacityofequipmentisrequiredmayberecognizedandprovisionmadefortheinstallationofadditionalequipment.Thusinstrumentationservesasaguideforfutureconstructioninagrowingpowersystem.Occasionally,underemergencyconditions,asystemoperatorobservesthathissystemloadexceedstheabilityoftheavailablegeneratingandtransmissionequipment.Heisthenfacedwiththeproblemofloadsheddingor,moreproperly,loadconservation.Itisthennecessarytodropselectedloadswhereserviceinterruptionisleastobjectionable.Insuchanevent,hereliesonthemanyinstrumentswhichprovideinformationrelativetosystem-operationconditions.Instrumentsmaysoundalarmsasadvancewarningsofconditionsrequiringactiontoavoiddamagetoequipmentoperatingbeyonditsdesignlimitation.Intheeventofextremeconditionssuchaspower-systemfaults,defectiveequipmentisswitchedoutofserviceautomatically.Instrumentsthatcontinuouslymonitorcurrentvoltage,andotherquantitiesmustbeabletoidentifythefaultedequipmentandtobringaboutoperationofthecircuitbreakerswhichremoveitfromservice,whileleavinginserviceallotherequipmentontheoperatingsystem.Themanydifferentelectricaldevicesonapowersystemandthoseownedbythecustomersaredesignedforoperationwithincertainspecifiedranges.Operation,excessivedeterioration,or(inextremecases)thedestructionofthedevice.Carefulattentiontotheconditionsunderwhichequipmentisoperatingmayindicatecorrectiveactionthatmustbetaken.Overcurrentonallelectricaldevicesisundesirable,asitproducesexcessivetemperatures,inefficientoperation,andreducedservicelife.Overcurrentinresidentialcircuitsmaybringaboutdisconnectionofthecircuitbyfuseorbreakeraction.Overcurrent