220kv变电站设计外文翻译

PAGE4PAGE1GeneralRequirementstoConstructionofSubstationSubstationsareavitalelementinapowersupplysystemofindustrialenterprises．Theyservetoreceive，convertanddistributeelectricenergy.Dependingonpowerandpurpose,thesubstationsaredividedintocentraldistributionsubstationsforavoltageof110-500kV;mainstep-downsubstationsfor110-220/6-10-35kV;deepentrancesubstationsfor110-330/6-10Kv;distributionsubstationsfor6-10Kv;shoptransformersubstationsfor6-10/0.38-0.66kV.Atthemainstep-downsubstations,theenergyreceivedfromthepowersourceistransformedfrom110-220kVusuallyto6-10kV(sometimes35kV)whichisdistributedamongsubstationsoftheenterpriseandisfedtohigh-voltageservices.Centraldistributionsubstationsreceiveenergyfrompowersystemsanddistributeit(withoutorwithpartialtransformation)viaaerialandcablelinesofdeepentrancesatavoltageof110-220kVovertheenterpriseterritory.Centraldistributionsubstationdiffersfromthemaindistributionsubstationinahigherpowerandinthatbulkofitspowerisatavoltageof110-220kV;itfeaturessimplifiedswitchingcircuitsatprimaryvoltage;itisfedfromthepowertoanindividualobjectorregion.Low-andmedium-powershopsubstationstransformenergyfrom6-10kVtoasecondaryvoltageof380/220or660/380.Step-uptransformersubstationsareusedatpowerplantsfortransformationofenergyproducedbythegeneratorstoahighervoltagewhichdecreaseslossesatalong-distancetransmission.ConvertersubstationsareintendedtoconvertACtoDC(sometimesviceversa)andtoconvertenergyofonefrequencytoanother.Convertersubstationswithsemiconductorrectifiersareconvertenergyofonefrequencytoanother.Convertersubstationswithsemiconductorrectifiersaremosteconomic.Distributionsubstationsfor6-10kVarefedprimarilyfrommaindistributionsubstations(sometimesfromcentraldistributionsubstations).Withasystemofdividingsubstationsfor110-220kV,thefunctionsofaswitch-gearareaccomplishedbyswitch-gearsfor6-10kVatdeepentrancesubstations.Dependingonlocationofsubstationstheirswitch-gearmaybeoutdoororindoor.Thefeedandoutputlinesat6-10kVsubstationsaremainlyofthecabletype.at35-220kVsubstationsoftheaerialtype.Whenerectingandwiringthesubstations,majorattentionisgiventoreliableandeconomicpowersupplyofagivenproduction.Substationsareerectedbyindustrialmethodswiththeuseoflargeblocksandassembliespreparedatthesiteshopsofelectricengineeringorganizationsandfactoriesofelectricalengineeringindustry.Substationsareusuallydesignedforoperationwithoutcontinuousattendanceofthedutypersonnelbutwiththeuseofelementaryautomaticandsignalingdevices.Whenconstructingthestructuralpartofasubstation.itisadvisabletouselight-weightindustrialstructuresandelements(panels,floors,etc.)madeofbentsections.Theseelementsarepre-madeoutsidetheerectionzoneandareonlyassembledatsite.Thisconsiderablycutsthetermsandcostofconstruction.Basiccircuitryconceptsofsubstationsarechosenwhendesigningapowersupplysystemoftheenterprise.Substationsfeatureprimaryvoltageentrances.transformersandoutputcablelinesorcurrentconductorsofsecondaryvoltage.Substationsaremountedfromequipmentandelementsdescribedbelow.Thenumberofpossiblecombinationsofequipmentandelementsisverygreat.Whenelaboratingasubstationcircuitry,itisnecessarytostriveformaximumsimplificationandminimizingthenumberofswitchingdevices.Suchsubstationsaremorereliableandeconomic.Circuitryissimplifiedbyusingautomaticreclosureorautomaticchangeovertoreservefacilitywhichallowsrapidandfaultlessredundancyofindividualelementsandusingequipment.Whendesigningtransformersubstationsofindustrialenterprisesforallvoltages,thefollowingbasicconsiderationsaretakenintoaccount:1.Preferableemploymentofasingle-bussystemwithusingtwo-bussystemsonlytoensureareliableandeconomicpowersupply;2.Wideuseofunitizedconstructionsandbuslesssubstations;3.Substantiatedemploymentofautomaticsandtelemetry;ifthesubstationdesigndoesnotenvisagetheuseofautomaticsortelemetry,thecircuitryissoarrangedastoallowforaddingsuchequipmentinfuturewithoutexcessiveinvestmentsandre-work.4.Useofsimpleandcheapdevices-isolatingswitches,short-circuitingswitches,load-breakingisolators,fuses,withdueregardfortheirswitchingcapacitymaydrasticallycuttheneedforexpensiveandcriticaloil,vacuum,solenoidandairswitches.Substationandswitch-gearcircuitriesaresomadethatusingtheequipmentofeachproductionlineisfedfromindividualtransformers,assemblies,thelinestoallowtheirdisconnectionsimultaneouslywithmechanismswithoutdisruptingoperationofadjacentproductionflows.Whenelaboratingcircuitryofasubstation,themostvitaltaskistoproperlychooseandarrangeswitchingdevices(switches,isolators,currentlimiters,arresters,high-voltagefuses).Thedecisiondependsonthepurpose,powerandsignificanceofthesubstation.Manyyearsago,scientistshadveryvagueideasaboutelectricity.Manyofthemthoughtofitasasortoffluidthatflowedthroughwiresaswaterflowsthroughpipes,buttheycouldnotunderstandwhatmadeitflow.Manyofthemfeltthatelectricitywasmadeupoftinyparticlesofsomekind,buttryingtoseparateelectricityintoindividualparticlesbaffledthem.Then,thegreatAmericanscientistMillikan,in1909,astoundedthescientificworldbyactuallyweighingasingleparticleofelectricityandcalculatingitselectriccharge.Thiswasprobablyoneofthemostdelicateweighingjobseverdonebyman,forasingleelectricparticleweighsonlyabouthalfofamillionthofapound.TomakeupapounditwouldtakemoreofthoseparticlesthantherearedropsofwaterintheAtlanticOcean.Theyarenostrangerstous,theseelectricparticles,forweknowthemaselectrons.Whenlargenumbersofelectronsbreakawayfromtheiratomsandmovethroughawire,wedescribethisactionbysayingthatelectricityisflowingthroughthewire.Yes,theelectricalfluidthatearlyscientiststalkedaboutisnothingmorethanelectricalflowingalongawire.Buthowcanindividualelectronsbemadetobreakawayfromatoms?Andhowcanthesefreeelectronsbemadetoalongawire?Theanswertothefirstquestionliesinthestructureoftheatomsthemselves.Someatomsaresoconstructedthattheyloseelectronseasily.Anatomofcopper,forexample,iscontinuallylosinganelectron,regainingit(oranotherelectron),andlosingitagain.Acopperatomnormallyhas29electrons,arrangedinfourdifferentorbitsaboutitsnucleus.Theinsideorbithas2electrons.Thenextlargerorbithas8.Thethirdorbitispackedwith18electrons.Andtheoutsideorbithasonlyoneelectron.Itisthisoutsideelectronthatthecopperatomiscontinuallylosing,foritisnotverycloselytiedtotheatom.Itwandersoff,isreplacedbyanotherfree-rovingelectron,andthenthissecondelectronalsowandersaway.Consequently,inacopperwirefreeelectronsarefloatingaroundinalldirectionsamongthecopperatoms.Thus,eventhroughthecopperwirelooksquitemotionlesstoyourordinaryeye,thereisagreatdealofactivitygoingoninsideit.Ifthewirewerecarryingelectricitytoanelectriclightortosomeotherelectricaldevice,theelectronswouldnotbemovingaroundatrandom.Instead,manyofthemwouldberushinginthesamedirection-fromoneendofthewiretotheother.Thisbringsustothesecondquestion.Howcanfreeelectronsbemadetomovealongawire?Well,menhavefoundseveralwaystodothat.Onewayischemical.Volta,svoltaicpile,orbattery,isachemicaldevicethatmakeselectricity(orelectrons)flowinwires.Anotherwayismagnetic.FaradayandHenrydiscoveredhowmagnetscouldbeusedtomakeelectricityflowinawire.MagnetsAlmosteveryonehasseenhorseshoemagnets-socalledbecausetheyareshapedlikehorseshoes.Probablyyouhaveexperimentedwithamagnet,andnoticedhowitwillpickuptacksandnails,orothersmallironobjects.Menhaveknownaboutmagnetsforthousandsofyears.Severalthousandyearsago,accordingtolegend,ashepherdnamedMagneslivedontheislandofCrete,intheMediterraneanSea.Hehadashepherdscrooktippedwithiron.Onedayhefoundanoddlyshapedblackstonethatstucktothisirontip.Later,whenmanyothersuchstoneswerefound,theywerecalledmagnets(afterMagnets).Thesewerenaturalmagnets.Inrecenttimesmenhavelearnedhowtomakemagnetsoutofiron.Moreimportantstill,theyhavediscoveredhowtousemagnetstopushelectronsthroughwires-thatis,howtomakeelectricityflow.Beforewediscussthis,therearecertaincharacteristicsofmagnetsthatweshouldknowabout.Ifapieceofglassislaidontopofahorse-shoesmagnet,andifironfilingsarethensprinkledontheglass,thefilingswillarrangethemselvesintolines.Ifthissamethingistridwithabarmagnet(ahorseshoemagnetstraightenedout),thelinescanbeseenmoreeasily.Theseexperimentsdemonstratewhatscientistscallmagneticlinesofforce.Magnets,theyexplain,workthroughlinesofforcethatext-endbetweenthetwoendsofthemagnet.Butelectronsseemtohavemagneticlinesofforcearoundthem,too.Thiscanbeprovedbystickingawirethroughapieceofcardboard,sprinklingironfilingsonthecardboard,andconnectingabatterytothewire.Thefilingswilltendtoformringsaroundthewire,asaresultofthemagnetismofthemovingelectrons(orelectricity).Sowecanseethatthereisarelationshipbetweenmovingelectronsandmagnetism,Magnetismresultsfromthemovementofelectrons.Ofcourse,electronsarenotreallyflowinginthebarmagnet,buttheyareinmotion,circlingthenucleioftheironatoms.However,inthemagnet,circlingthelinedupinsuchawaythattheirelectronsarecirclinginthesamedirection.Perhapsagoodcomparisonmightbeagreatnumberofboyswhirlingballsonstringsinaclockwisedirectionaroundtheirheads.