T外文文獻(xiàn)：SelectionandCoolingofPowerTransformerTheselectionofthetransformercanhaveamajorimpactonthecostasubstation,sincethetransformerrepresentsthemajorcostitem.Nameplateratingisonlyaguidetotransformerapplication,andshouldonlybeusedasafirststepintheselectionprocess.Thetransformerisavailableasaself-cooledunit,oritcanbepurchasedwithadditionalstepsofforcedcoolingthatusefanorfansandoilpumps.Transformerratingscanbeincreasedfrom25%to66%bytheadditionoffansandpumps.Thenameplateratingisbasedonacontinuousloadproducinga55℃to65℃conductortemperatureriseoverambient.Sincemanytransformersdonotcarrycontinuousloads,advantagecanbegainedfromthethermaltimelagtocarryhigherpeakloadswithoutexceedingthetemperaturelimits.Transformerratingsarebasedontheassumptionthatonlyanextremelyslowdeteriorationofinsulationwilltakeplacewithnormaloperation.Asubstantialincreaseinratingcanbeachievedbyacceleratingthelossofinsulationlife.Thisincreaseinratingmightapproach200%foranhourortwo,andapproximately120%for24hours.Forsubstationsthataredesignedtocarryfullloadundertheoutageofanyonetransformer,ahighemergencyratingfora24-hourperiod(e.g.untilthefailedunitcanbereplaced)couldmeantheselectionofsmallertransformersandasubstantialsavinginsubstationcost.Theselectionofthetransformershouldinvolveacarefulevaluationofanumberofotherfactors：(1)Impedancesshouldbeselectedconsideringtheireffectonshort-circuitdutiesandlow-sidebreakerratingsbothforinitialandfuturestationdevelopments.Inaddition,impedanceisimportanttoachieveaproperloaddivisionintheparalleloperationoftransformers..(2)Noloadtaprangesshouldbeselectedtoprovideanadequatelow-sidebusvoltage.(3)Ifthehigh-sideorlow-sidevoltagesvaryoverawiderangeduringtheloadcycle,itmaybenecessarytoprovidebusregulation.Theactualregulationcanbecalculatedusingthesystemandloadcharacteristics.Ifregulatingequipmentisneeded,itmaybedesirabletoprovideitinthetransformerbyusingloadtapchanger(LTC)equipment.Iftheneedforbusregulationisnotpresentlyevident,butmayberequiredinthefuture,itmaybeeconomicaltoleavespaceinthestationforfutureregulators,andbuytransformerswithoutLTCequipment.Agreatmanytransformers,includingallthelargeonesandallthehighvoltageonesareimmersedinmineraloilwhichservesthedoublepurposeofcoolingandinsulatingthewindings.Smalltransformershaveenoughtanksurfacetoradiateal1theheatcausedbytheirlosseswithoutexceedingthepermissibletemperaturerise.Assizeincreases,thelossesincreasefasterthanthetanksurfacewhichsoonbecomesinadequate.Variousmethodshavebeendevelopedtogettheheatoutofthetankmoreeffectively.Largepowertransformerbeingbuilttodayarecommonlyoftheforced-oil-cooledtype.Inthisdesigntheoilispumpedboththroughtheexternalcoolingdevices(airorwaterheat-exchangers)andthroughinternalchannelsthatarelocatednearestthepointswheretheheatisgenerated.Thusthetransferofheattoandfromtheoilisfarmoreeffectivethanintheplainself-cooledorfan-cooledunitwheretheoilisallowedtocirculatebyconvection.Whenoil-to-airheatexchanger(agroupfansoneachradiator)isused,thiscoolingtypeisdesignatedastypeofFOA.Whileoil-to-waterheatexchangerisused,itiscalledFOW.Forapplicationswhereanyliquid,evenanonflammableone,isobjectionable,thedry-typetransformerisused.Theventilateddry-typeunitiscooledbyacontinuousnaturaldraftofairandconsequentlyisnotsuitableforlocationswheretheairiswetordirty.Fortheselocationsacompletelyenclosedunit,thesealeddry-type,isavailable,havingacore-and-coilinatankthatissealedandfilledwithaninsulatinggas.Dry-typetransformersarecompletelynonflammable,usingorganicmaterialsuchasepoxyresin.中文譯文：電力變壓器的選擇和冷卻變壓器的選擇對(duì)變電所的建造成本具有重大影響，因?yàn)樽儔浩魇侵饕某杀卷?xiàng)目。銘牌定額只是變壓器應(yīng)用的指南,它只應(yīng)該用作變壓器選擇過程的第一步。變壓器可以是自冷式單位，也可以購(gòu)買額外的冷卻裝置,如強(qiáng)制冷卻風(fēng)機(jī)或機(jī)組和柴油泵。根據(jù)額外的冷卻機(jī)組和柴油泵，變壓器評(píng)級(jí)可以從25%增加到66%O銘牌評(píng)級(jí)是基于連續(xù)負(fù)荷產(chǎn)生超過環(huán)境55c到65c導(dǎo)體溫升而評(píng)定的。？？？因?yàn)楹芏嘧儔浩鞑粠нB續(xù)負(fù)載,優(yōu)勢(shì)可以獲得從熱滯后時(shí)間進(jìn)行更高的高峰負(fù)荷而不超過溫度限制。變壓器的評(píng)級(jí)是基于假設(shè)：正常操作下的絕緣老化只是一個(gè)極其緩慢的過程。通過加速絕緣老化的進(jìn)程可以大幅度的提高評(píng)定等級(jí)。在一兩個(gè)小時(shí)左右評(píng)級(jí)可能增長(zhǎng)接近200%,而在在二十四小時(shí)左右評(píng)級(jí)則增長(zhǎng)大約120虬因?yàn)樽冸娬镜脑O(shè)計(jì)要保證在任何一個(gè)變壓器斷電的情況下都要滿足全負(fù)荷運(yùn)行，為24變電站設(shè)計(jì)將滿載在停機(jī)的任何一個(gè)變壓器,因此在二十四小時(shí)內(nèi)的較高的緊急評(píng)級(jí)(例如直到失敗的單位可以更換)可能意味著選擇較小的變壓器和節(jié)約大量的變電所成本。變壓器的選擇應(yīng)該涉及對(duì)其他影響因素的審慎評(píng)估：(1)阻抗應(yīng)該被選擇的考慮到他們對(duì)短路職責(zé)和下部斷路器評(píng)級(jí)的影響對(duì)初始和未來空間站發(fā)展。此外，阻抗在并行變壓器的操作中獲得一個(gè)合適的負(fù)載也是十分重要的.⑵無載分接范圍應(yīng)該選擇提供一個(gè)足夠的下部總線電壓。(3)如果高壓側(cè)或低壓側(cè)電壓在負(fù)載周期內(nèi)變化很大的話，可能有必要提供總線監(jiān)管。通過系統(tǒng)和負(fù)載特性實(shí)際監(jiān)管和控制是可以被計(jì)算和描繪的。如果調(diào)節(jié)設(shè)備是必要的，在變壓器內(nèi)使用負(fù)載抽頭轉(zhuǎn)換開關(guān)（LTC）設(shè)備來提供監(jiān)管是可取的。如果需要總線監(jiān)管目前是不需要的,但可能在未來需要的，那么在變電站預(yù)留未來安裝設(shè)備的空間并且購(gòu)買沒有LTC設(shè)備的變壓器是十分經(jīng)濟(jì)的。許多變壓器,包括所有的大體積的和所有的高電壓的變壓器都是沉浸在礦物油,礦物油有雙重目的：冷卻和絕緣繞組。小變壓器有足夠的容器表面輻射all熱引起的損失而不超過容許溫度上升范圍。隨著體積的增加,損失增加的速度會(huì)加快，這時(shí)容器表面會(huì)變得不適宜。很多的方法已經(jīng)被改進(jìn)以使的容器的散熱更有效。今天一般建造的大型電力變壓器都是強(qiáng)制循環(huán)油冷卻類型的。在這個(gè)設(shè)計(jì)中礦物油通過油泵不僅流進(jìn)外部冷卻設(shè)備（空氣或水熱交換器），而且流過內(nèi)部最靠近熱源的凹槽。因此通過礦物油對(duì)熱量進(jìn)行轉(zhuǎn)移的方式