第九章操作過電壓與絕緣配合課件

第九章操作過電壓與絕緣配合

Chapter9OperationOver-voltage&InsulationCoordination

操作過電壓通常具有幅值高、存在高頻振蕩、強阻尼和持續(xù)時間短的特點，危害性極大。Typicalover-voltagehasahighamplitude.Thereareseveralharmfulcharacteristicsofhigh-frequencyoscillation,strongdampingandshortduration.第九章操作過電壓與絕緣配合

Chapter9Oper常見的操作過電壓主要包括：切斷空載線路過電壓、空載線路合閘過電壓、切除空載變壓器過電壓和斷續(xù)電弧接地過電壓這幾種。Commonover-voltageoperationsinclude:cuttingoffno-loadlines,closingonno-loadlines,removingno-loadtransformersandintermittentarcgrounding.常見的操作過電壓主要包括：切斷空載線路過電壓、空載線路合閘過絕緣配合是指綜合考慮系統(tǒng)中可能出現(xiàn)的各種作用電壓、保護(hù)裝置特性及設(shè)備的絕緣特性，最終確定電氣設(shè)備的絕緣水平。Insulationcoordinationisanintegratedsystemconsideringvarioustypesofover-voltage,insulationcharacteristicsofprotectivedevicesandequipment,Whichdeterminetheinsulationlevelofelectricalequipment.絕緣配合是指綜合考慮系統(tǒng)中可能出現(xiàn)的各種作用電壓、保護(hù)裝置特9.1切斷空載線路過電壓(Cuttingoffno-loadlinesover-voltage)9.2空載線路合閘過電壓(Closingonno-loadlinesover-voltage)9.3切除空載變壓器過電壓(Removingno-loadtransformersover-voltage)9.4斷續(xù)電弧接地過電壓(Intermittentarcinggroundover-voltage)

9.5絕緣配合(Insulationcoordination)習(xí)題和參考答案(Exercisesandreferences)

本章內(nèi)容(Maincontentofthissection)返回本章內(nèi)容(Maincontentofthis9.1切斷空載線路過電壓(Cuttingoffno-loadlinesover-voltage)

切除空載線路是電網(wǎng)中常見操作之一，在切空載線路的過程中，雖然斷路器切斷的是幾十安到幾百安的電容電流，比短路電流小的多，但如果使用的斷路器滅弧能力不強，在切斷這種電容電流時就可能出現(xiàn)電弧的重燃，從而引起電磁振蕩，造成過電壓。Cuttingoffno-loadlinesisoneofthecommonoperationsinpowergrid.Intheprocessofcuttingloadline,althoughthecircuitbreakercutsoffthetenstohundredsampereofcapacitivecurrentwhichissmallerthantheshort-circuitcurrent,thearcmayre-ignite,whichcauseselectromagneticvibration,resultinginover-voltageifthecircuitbreaker’scapabilitytoeliminatearcisnotstrong.9.1切斷空載線路過電壓切除空載線路是電網(wǎng)中本節(jié)內(nèi)容(Contentofthissection)

9.1.1產(chǎn)生原理

(Generationtheory)9.1.2影響因素和降壓措施

(Influencingfactorsandreducevoltagemeasures)本節(jié)內(nèi)容(Contentofthissection)

用單相集中參數(shù)的簡化等效電路來分析，如圖9-1，S斷開之前線路電壓UC(t)=e(t),設(shè)第一次熄?。ㄔO(shè)時間為t1）發(fā)生斷路器的工頻電容電流ic(t)過零時，如圖9-2，線路上電荷無處泄放，uc(t)保留為Em，觸頭間電壓ur(t)為:9.1.1產(chǎn)生原理(Generationtheory)Single-phaselumpedparametercircuitshowninfigure9-1isusedasthesimplifiedequivalentcircuittoanalyze.BeforeSisdisconnectedlinevoltageUC(t)=e(t).Supposethefirstarcextinction(thetimeist1)occurswhencircuitbreakerpowerfrequencycapacitivecurrentic(t)showedinfigure9-2crosseszero.Thechargeinthelinehasnoplacetodischarge,souc(t)remainsequalingEm.Contactvoltageur(t)is:

Ur(t)=e(t)-Em=Em(coswt-1)(9-1)用單相集中參數(shù)的簡化等效電路來分析，如圖9-1，S斷圖9-1切除空載線路時的等值計算電路圖Fig9-1

Equivalentcalculationcircuitdiagramwhencuttingofftheno-loadlines圖9-2切除空載線路過電壓的發(fā)展過程Fig9-2Over-voltagedevelopmentofcuttingoffno-loadlines圖9-1切除空載線路時的等值計算電路圖Fig9-1EquHalfcyclelater,e(t)=-Em.Thevoltagebetweentwocontactsrecoversto2Em

.Atthemomentifdielectricinsulationstrengthbetweenthecontactshasnotbeenproperlyrestored,orthestrengthofinsulationrecoverydoesnotrisefastenough,thearcmayre-ignitewhent2

,whichisequivalenttoananti-polarityreclosing.半周期后，e(t)=-Em，兩觸頭間電壓即恢復(fù)電壓2Em。此時若觸頭間的介質(zhì)絕緣強度沒有很好恢復(fù)，或絕緣恢復(fù)強度的上升速度不夠快，可能在t2時電弧重燃，相當(dāng)于一次反極性重合閘。Halfcyclelater,e(t)=-Em.ThUCmax達(dá)到-3Em，設(shè)在t＝t3時高頻(重合閘過程，回路振蕩的角頻率,大于工頻下的M)電容電流第一次過零時熄弧，uc(t)

保持-3Em，又過T／2，e(t)又達(dá)最大值，觸頭間電壓ur(t)為4Em。依此類推，直至觸頭間絕緣足夠高，不再重燃為止。線路上的過電壓將不斷增大，一直達(dá)到很高的數(shù)值。返回圖9-2切除空載線路過電壓的發(fā)展過程Fig9-2Over-voltagedevelopprocessofcuttingoffno-loadlineUCmaxreaches-3Em,supposingatt＝t3thehigh-frequency(re-closingprocess,looposcillationangularfrequency,isgreaterthanM)capacitivecurrentcrosseszeroforthefirsttimeandarcisextinct.uc(t)remains-3Em.AfterT/2,e(t)reachesthemaximumvoltage.ur(t)is4Em,andsoon.Untiltheinsulationbetweencontactsishighenough,arcwillnolongerre-ignite.Over-voltageinlineswillcontinuetoincreasetoaveryhighvalue.UCmax達(dá)到-3Em，設(shè)在t＝t3時高頻(9.1.2影響因素和降壓措施(Influencingfactorsandreducevoltagemeasures)

影響過電壓的最大值的因素：

(Influencingfactorsofthemaximumover-voltage)1)斷路器的性能；

(Theperformanceofcircuitbreakers)

2)中性點接地方式；(Typeofneutralgrounding)9.1.2影響因素和降壓措施影響過電壓的最大值的因素：3)母線上的出線數(shù)

(Theoutletnumberofbus)

4)在斷路器外側(cè)裝有電磁式電壓互感器等設(shè)備(Electromagneticvoltagetransformerandotherequipmentoutsidethecircuitbreakers)消除或降低操作過電壓采取的措施如下：(Measurestoeliminateorreducetheover-voltageareasfollows:)

（1）改善斷路器的結(jié)構(gòu)，避免發(fā)生重燃現(xiàn)象

(Improvethestructureofcircuitbreakertoavoidarcregenerating)3)母線上的出線數(shù)（2）斷路器加裝并聯(lián)電阻(

Installingcircuitbreakerwithparallelresistors)

（3）利用避雷器保護(hù)(Usesurgearresterstoprotect)

（4）泄流設(shè)備的裝設(shè)(Installingequipmentfordischarge)（2）斷路器加裝并聯(lián)電阻圖9-3帶并聯(lián)電阻斷路器Fig9-3Circuitbreakerwithparallelresistors1—主觸頭2—輔助觸頭R—并聯(lián)電阻1—Maincontact2—AuxiliarycontactR—Parallelresistors圖9-3帶并聯(lián)電阻斷路器產(chǎn)生原理(Generationtheory)原理(Theory)優(yōu)點(Benefits)缺點(Shortcomings)影響因素和降壓措施(Influencingfactorsandreducevoltagemeasures)小結(jié)(Summary)影響過電壓的最大值的因素（4點）

Factors

affectingthemaximumover-voltage(4points)返回（本節(jié)完）產(chǎn)生原理(Generationtheory)小結(jié)9.2空載線路合閘過電壓(Closingonno-loadlinesover-voltage)

電力系統(tǒng)中，空載線路合閘過電壓也是一種常見的操作過電壓。通常分為兩種情況，即正常操作和自動重合閘。由于初始條件的差別，重合閘過電壓的情況更為嚴(yán)重。近年來由于采用了種種措施（如采用不重燃斷路器、改進(jìn)變壓器鐵芯材料等）限制或降低了其他幅值更高的操作過電壓，空載線路合閘過電壓的問題就顯得更加突出。Closingonno-loadlinesover-voltageisalsoacommonover-voltageinpowersystem.Itisusuallydividedintotwokindsthatarenormaloperation

andautomaticreclosing.Duetodifferencesininitialconditions,situationofreclosingover-voltageisworse.Inrecentyears,becausevariousmeasureshadbeentaken(suchasusingcircuitbreakerswhicharenotrenewed,improvingtransformers’corematerials,etc.)tolimitorreducetheamplitudeofotheroperationover-voltagewithhigheramplitude.Theproblemoftheclosingonno-loadlinesover-voltagebecomesevenmoreapparent.9.2空載線路合閘過電壓電力系統(tǒng)中，本節(jié)內(nèi)容(Contentinthissection)9.2.1發(fā)展過程

(Developprocess)9.2.2影響因素和降壓措施

(Influencingfactorsandreducevoltagemeasures)

本節(jié)內(nèi)容(Contentinthissection)9

這種操作通常出現(xiàn)在線路檢修后的試送電。此時線路上不存在任何異常（如接地）。線路電壓的初始值為零。正常合閘時，若三相接線完全對稱，且三相斷路器完全同步動作，則可按照單相電路進(jìn)行分析研究。在這里我們用集中參數(shù)等值電路的方法分析這種過電壓的發(fā)展機理。Suchoperationoftenappearsinlinesfortrialimmediatelyafterinspectionofpowerlines.Atthemomenttheyarenormal(suchasgrounding).Theinitialvalueoflinevoltageiszero.Innormalclosingoperation,ifthree-phaseconnectionarecompletelysymmetrical,andthree-phasecircuitbreakershavesynchronizedaction,itcanbeanalyzedassingle-phasecircuit.Hereweuselumpedparameterequivalentcircuittoanalyzethemechanismofdevelopmentoftheover-voltage.1.正常合閘的情況(Normalconditions)

9.2.1發(fā)展過程(Developprocess)這種操作通常出現(xiàn)在線路檢修后的試送電。此時線路上不存圖9-4合閘示意圖Fig9-4Closingdiagram

（a）集中參數(shù)等值電路（b）簡化等值電路(a)Lumpedparameterequivalentcircuit(b)Simplifiedequivalentcircuit圖9-4合閘示意圖(a)Lumpedparameter

在圖9-4(a)所示的等值電路中，其中空載線路用一T型等值電路來代替,RT、LT、CT分別為其等值電阻、電感和電容，u為電源的電阻和電感。在作定性分析時，還可忽略電源和線路電阻的作用，這樣就可進(jìn)一步簡化成圖9-4(b)所示的簡單振蕩回路，其中電感。若取合閘瞬間為時間起算點(t＝0)，則電源電壓的表達(dá)式為Figure9-4(a)showsaequivalentcircuit,whichno-loadlineisreplacedbyaT-equivalentcircuit.RT,LT,CTstandfortheequivalentresistance,inductanceandcapacitancerespectively.uispowerresistanceandinductance.Powerandlineresistancecanbeignoredwhenmakingqualitativeanalysis.Thusitcanbefurthersimplifiedtoasimpleoscillatorcircuitshowninfigure9-4(b).Ifclosingtimeistakenasstarting-point(t=0),thepowervoltagecanbedescribedasfollowed.在圖9-4(a)所示的等值電路中（9-2）（9-3）UΦ為穩(wěn)態(tài)分量；(UΦthesteady-statecomponent)

UΦ

為自由振蕩分量。(UΦfreeoscillationcomponent)（9-2）（9-3）UΦ為穩(wěn)態(tài)分量；UΦ（9-5）再者，電源是工頻交流電壓u(t),這時uc(t)表達(dá)式將為Furthermore,thepowervoltageu(t)isACvoltage.Theexpressionofuc(t)willbe（9-4）回路存在衰減的振蕩，以衰減系數(shù)δ來表示：Theattenuationoscillationexistsintheloop.Useattenuationcoefficientδtoexpressoscillation:（9-5）再者，電源是工頻交流電壓u(t),這時uc(t)表波形如圖9-5(b）WaveformisshowninFigure9-5(b)圖9-5合閘過電壓波形Fig9-5Closingover-voltagewaveform

(a)電源電壓為直流電壓(b)電源電壓為工頻交流電壓(a)DCsupplyvoltage

(b)ACsupplyvoltage

波形如圖9-5(b）Waveformisshownin

以上是正常合閘的情況，空載線路L沒有殘余電荷，初始電壓UC(0)＝0。如果是自動重合閘的情況，那么條件將更為不利，主要原因在于這時線路上有一定殘余電荷和初始電壓，重合閘時振蕩將更加激烈。Innormalclosingconditions,thereisnoresidualchargeonno-loadlinesL.TheinitialvoltageUC(0)=0.Inautomaticreclosingoperation,theconditionswillbemoreseriousmainlybecausethereisacertainresidualchargeandinitialvoltage.Thustheoscillationwillbemoreintensewhenitisre-closed.2.自動重合閘的情況(Automaticre-closing)以上是正常合閘的情況，空載線路L沒有殘余電荷，自動重合閘是線路發(fā)生跳閘故障后，由自動裝置控制而進(jìn)行的合閘操作。Automaticre-closingareoperationscarriedoutunderthecontrolofautomaticequipmentafterafaulttripoccursonline.自動重合閘是線路發(fā)生跳閘故障后，由自動裝置控

圖9－6為系統(tǒng)中常見的單相短路故障的示意圖。在中性點直接接地系統(tǒng)中，A相發(fā)生對地短路，短路信號先后到達(dá)斷路器Q2,Q1。斷路器S2先跳閘，在斷路器Q2跳開后，流過斷路器Q1中鍵全相的電流是線路電容電流，故當(dāng)電壓電流相位相差900時，斷路器Q1跳閘。于是在健全相線路上將留有殘余電壓。Figure9-6showsthecommonsingle-phaseshort-circuitinpowersystem.Intheneutralpointdirectgroundingsystem,shortcircuitoccurswhenA-phasegrounds.Short-circuitsignalgetstocircuitbreakersQ2andthenQ1.ThetripoccursfirstinthecircuitbreakerS2.Afterthatthelinecurrentinthekey-phaseflowingthroughthecircuitbreakerQ1iscapacitivecurrent.Sowhenthedifferenceofvoltageandcurrentphaseis90degree,thetripoccursincircuitbreakerQ1.Residueswillbeleftinnormalphasevoltagelines.圖9－6為系統(tǒng)中常見的單相短路故障的示意圖。在圖9-6重合閘示意Fig9-6Reclosingdiagram圖9-6重合閘示意

設(shè)Q1重合閘之前，線路殘余電壓已下降30％，即(1－0.3）×(1.3~1.4UΦ)=(0.91～0.98)UΦ?？紤]最嚴(yán)重的情況，重合閘時電源電壓為－UΦ，重合閘時暫態(tài)過程中過電壓為－UΦ＋[-UΦ-(0.91～.98)UΦ]=(-2.91～2.98)UΦ。在實際過程中，過電壓還要低些。在合閘過電壓中，以三相重合閘的情況最為嚴(yán)重。

返回SupposebeforeQ1isreclosed,residualvoltageonthelinehasdropped30percent,thatis(1-0.3)×(1.3~1.4UΦ)=(0.91~0.98)UΦ.Consideringthemostseriouscase,thesupplyvoltageis-UΦwhenre-closingandinthetransientprocessofreclosingtheover-voltageis-UΦ+[-UΦ-(0.91~.98)UΦ]=(-2.91~2.98)UΦ.Inpracticalprocess,over-voltageisevenlower.Intheclosingover-voltage,thethree-phasereclosingisthemostseriouscondition.設(shè)Q1重合閘之前，線路殘余電壓已下降30％，9.2.2影響因素和降壓措施(Influentialfactorsandstep-downmeasures)

以上對合閘過電壓的分析也是考慮最嚴(yán)重的條件、最不利的情況。實際出現(xiàn)的過電壓幅值會受到一系列因素的影響，最主要的有：Theaboveanalysisofclosingover-voltageconditionsisinthemostserious,themostadverse

circumstance.Theactualover-voltageamplitudewillbesubjecttoanumberoffactors.Themostimportantonesare:合閘相位(Closingphase)

線路損耗(LineLoss)線路殘余電壓的變化

(Changesofresidualinline)9.2.2影響因素和降壓措施以上對合閘過電壓1.合閘相位(Closingphase)

合閘時電源電壓的瞬時值取決于它的相位，相位的不同直接影響著過電壓幅值，若需要在較有利的情況下合閘，一方面需改進(jìn)高壓斷路器的機械特性，提高觸頭運動速度，防止觸頭間預(yù)擊穿的發(fā)生；另一方面通過專門的控制裝置選擇合閘相位，使斷路器在觸頭間電位極性相同或電位差接近于零時完成合閘。Whenclosingthesupplyvoltage,theinstantaneousvaluedependsonitsphase.Thephasedifferencedirectlyaffectstheover-voltageamplitude.Ifweneedtocloseinmorefavorablecircumstances,ontheonehandweshouldimprovethemechanicalpropertiesofhigh-voltagecircuitbreakerstoincreasethevelocityofcontacttopreventthepre-breakdownbetweencontacts;ontheotherhand,useaspecialcontroldevicetoselectclosingphase,sothatcircuitbreakercancompletetheclosingwhenthepolaritiesoftheelectricpotentialbetweencontactsarethesameordifferenceisclosetozero.1.合閘相位(Closingphase)2.線路損耗(LineLoss)

線路上的電阻和過電壓較高時線路上產(chǎn)生的電暈都構(gòu)成能量的損耗，消耗了過渡過程的能量，使得過電壓幅值降低。Thecoronaproducedwhenresistanceandover-voltageonlinesarehighconstitutestheenergyloss,whichconsumestheenergyinthetransitionprocesstolowerover-voltageamplitude.

2.線路損耗(LineLoss)Intheautomaticreclosingprocess,becausethereisacertainleakageresistanceofinsulators,about0.5sintervalperiod,residualvoltageinlinewilldrop10%~30%.Thenithelpstoreducethemagnitudeofreclosingover-voltage.Inaddition,iftheline-sideaccesswithelectromagneticvoltagetransformer,itsequivalentinductanceandequivalentresistanceandlinecapacitancetogetherconstituteadampedoscillationcircuit,sothattheresidualchargecandischargecompletelyinafewpowerfrequencycycles.3.線路上殘壓的變化(Changesofresidualinline)

在自動重合閘過程中，由于絕緣子存在一定的泄漏電阻，大約有0.5s的間歇期，線路殘壓會下降10％～30％。從而有助于降低重合閘過電壓的幅值。另外如果在線路側(cè)接有電磁式電壓互感器，那么它的等值電感和等值電阻與線路電容構(gòu)成一阻尼振蕩回路，使殘余電荷在幾個工頻周期內(nèi)泄放一空。Intheautomaticreclosingpro合閘過電壓的限制、降低措施主要有:(Limitandreducingmeasuresofclosingover-voltageare:)(一)裝設(shè)并聯(lián)合閘電阻——最有效的措施(Installationof

co-gateresistance-themosteffectivemeasure)

圖9-3帶并聯(lián)電阻斷路器Fig9-3Circuitbreakerwithparallelresistance

如圖9-3所示，這時應(yīng)先合輔助觸頭2、后合主觸頭1。AsshowninFigure9-3,

auxiliarycontact2shouldbefirstclosed,andthenthemaincontact1shouldbeclosed.合閘過電壓的限制、降低措施主要有:(一)裝設(shè)并聯(lián)合閘電阻——整個合閘過程的兩個階段對阻值的要求是不同的：在合輔助觸頭2的第一階段，R對振蕩起阻尼作用，使過渡過程中的過電壓最大值有所降低，R越大、阻尼作用越大、過電壓就越小，所以希望選用較大的阻值；大約經(jīng)過8～15ms，開始合閘的第二階段，主觸頭1閉合，將R短接，使線路直接與電源相連，完成合閘操作。Intheentireclosingprocess,therequirementsofresistanceintwostagesaredifferent.Inthefirststagewhenclosingtheauxiliarycontact2,RdampstheoscillationSothatthemaximumofover-voltagedecreasesinthetransitionalprocess.ThelargerRis,thegreaterthedampingeffectis.Andthenover-voltageissmaller.Soalargeresistanceisfavorable.Afterabout8~15ms,secondstageofclosingbegins.Themaincontact1isclosed,Rshorted,sothatthelineisconnectedwiththepowerdirectlytocompletetheclosingoperation.整個合閘過程的兩個階段對阻值的要求是不同的：

在第二階段，R值越大，過電壓也越大，所以希望選用較小的阻值。因此，合閘過電壓的高低與電阻值有關(guān)，某一適當(dāng)?shù)碾娮柚迪驴蓪⒑祥l過電壓限制到最低。圖9-7為500kV開關(guān)并聯(lián)電阻與合閘過電壓的關(guān)系曲線，當(dāng)采用450Ω的并聯(lián)電阻時，過電壓可限制在2倍以下。Inthesecondstage,thegreatervalueRis,thegreatertheover-voltageis.Sosmallerresistanceisfavorable.Therefore,thelevelofclosingover-voltageisrelatedtoresistancevalues.Anappropriateresistorvaluemaylimittheclosingover-voltagetoaminimum.Figure9-7showstherelationshipcurveof500kVswitchingparallelresistanceandclosingover-voltage,whenusinga450Ωparallelresistance,over-voltagemaybelimitedlessthantwotimes在第二階段，R值越大，過電壓也越大，所以希望選用較小圖9-7合閘電阻R與過電壓倍數(shù)K0的關(guān)系Fig9-7TherelationshipbetweenclosingresistorRandtheover-voltagemultipleK0圖9-7合閘電阻R與過電壓倍數(shù)K0的關(guān)系（2）控制合閘相位(Controlofclosingphase)

通過一些電子裝置來控制斷路器的動作時間，在各相合閘時，將電源電壓的相位角控制在一定范圍內(nèi)，以達(dá)到降低過電壓的目的。具有這種功能的同電位合閘斷路器在國外已研制成功．它既有精確、穩(wěn)定的機械特性、又有檢測觸頭間電壓(捕捉向電位瞬間)的二次選擇回路。Thecircuitbreakeroperatingtimecanbecontrolledbyelectronicdevices.Duringtheclosingpesiodofeachphase,thephaseangleofsupplyvoltageiscontrolledinacertainrangeinordertoachievethepurposeofreducingover-voltage.Thepotentialclosingcircuitbreakerswiththisfunctionhavebeendevelopedinforeigncountries,whichhavebothaccuracyandstablemechanicalpropertiesandthesecondselectioncircuit,detectingthevoltagebetweencontacts(capturingthepotentialmoment).（2）控制合閘相位(Controlofclosing（3）利用避雷器來保護(hù)(Protectingusingthesurgearresters)

安裝在線路首端和末端(線路斷路器的線路側(cè))的ZnO或磁吹避雷器，均能對這種過電壓進(jìn)行限制，如果采用的是現(xiàn)代ZnO避雷器，就有可能將這種過電壓的倍數(shù)限制到1.5～1.6。ZnOormagnetismblowingarresterinstalledatthelineheadandend(line’sideoflinecircuitbreaker)canlimitthiskindofovervoltage.Thereispossibilitytolimitthiskindofovervoltagemultipleby1.5~1.6timesifmodernZnOarresteris（3）利用避雷器來保護(hù)(Protectingusing發(fā)展過程(Developprocess)正常合閘的情況(Thenormalclosingcondition)自動重合閘的情況(Automaticre-closingcondition)影響因素和降壓措(Influentialfactorsandstep-downmeasures)合閘相位(Closingphase)線路損耗(LineLoss)線路殘余電壓的變化(Residualchangesinlinevoltage)小結(jié)(Summary)返回（本節(jié)完）發(fā)展過程(Developprocess)小結(jié)(Sum9.3切除空載變壓器過電壓Removalofno-loadtransformerover-voltage

正常運行時,空載變壓器表現(xiàn)為一勵磁電感。切除空載變壓器就是開斷一個小容量電感負(fù)荷，會在變壓器和斷路器上出現(xiàn)很高的過電壓。開斷并聯(lián)電抗器、電動機等，也屬于切斷感性小電流的情況。Duringthenormaloperation,no-loadtransformeractsasanexcitationinductor.Removalofno-loadtransformerisbreakingasmall-capacityinductanceload,andahighover-voltagewillappearontransformersandcircuitbreakers.Breakingshuntreactor,motor,arealsobelongtothesituationofcuttingoffasmallemotionalcurrent.9.3切除空載變壓器過電壓正常運行時,空載變壓本節(jié)內(nèi)容(Contentofthissection)9.3.1發(fā)展過程(Development)

9.3.2影響因素與限制措施

(Influencingfactorsandrestrictivemeasures)本節(jié)內(nèi)容(Contentofthissection)

變壓器和斷路器上出現(xiàn)過電壓的原因是變壓器的空載電流過零前就被斷路器強制熄弧而切斷，導(dǎo)致全部電磁能量轉(zhuǎn)化為電場能量而使電壓升高。Thereasonwhyover-voltageappearsontransformerandcircuitbreakeristhatbeforetransformerno-loadcurrentcrosseszero,ithasbeenshutoffbycircuitbreaker’mandatoryextinction.Alltheelectromagneticenergyischangingintoelectricenergywhichincreasesvoltage.9.3.1發(fā)展過程(Development)變壓器和斷路器上出現(xiàn)過電壓的原因是變壓器的空

研究表明：切斷100A以上的交流電流時，開關(guān)觸頭間的電弧通常是在工頻電流自然過零時熄滅的；當(dāng)所切除的電流很小時（變壓器的空載電流非常小，只有幾安到幾十安），電弧往往提前熄滅，亦即電流會在過零之前就被強行切斷，即所謂的截流現(xiàn)象。Itisdemonstratedthatwhencuttingoffcurrentismorethan100AAC,thearcusuallyextinguisheswhenfrequencycurrentisoverzeronaturallybetween

contacts.Whenthecurrenttoberemovedisverysmall(thetransformerno-loadcurrentisverysmall,onlyafewANtoscoresAN),thearcoftenextinguishesbeforehand.Thatistosaythecurrentswillbeforciblycutoffbeforetheyareoverzero,thatis,thephenomenonoftheso-calledclosure.研究表明：切斷100A以上的交流電流時，開關(guān)觸

可用圖9-8所示的簡化等值電路來說明這種過電壓的發(fā)展過程。圖中為變壓器的激磁電感，為變壓器繞組及連接線的對地電容。Figure9-8showsthesimplifiedequivalentcircuittoillustratethedevelopmentofover-voltage.Inthefigureforthetransformermagnetizinginductance,forthetransformerwindingandconnectingtheline-to-groundcapacitance.圖9-8切除空載變壓器的理想等值電路Fig9-8Theidealequivalentcircuitofremovalofno-loadtransformer可用圖9-8所示的簡化等值電路來說明這種過電壓的發(fā)

假如空載電流時發(fā)生截斷（即由突然降到零），此時電源電壓為，則切斷瞬間在電感和電容中所儲存的能量分別為:Iftheno-loadcurrentoftruncationoccurs(thatissuddenlyreducestozero),atthistimethesupplyvoltageis,thenthemomentwhencutofftheenergystoredintheinductorandcapacitor,whichareshowedbelow:

假如空載電流時發(fā)生截斷（此后即在、構(gòu)成的振蕩回路中發(fā)生電磁振蕩，在某一瞬間，全部電磁能量均變?yōu)殡妶瞿芰?，這時電容上出現(xiàn)最大電壓Thereafterelectromagneticoscillationsoccuratoscillationcircuitcomposedby、

.Inacertainmoment,alltheelectromagneticenergytransformsintoelectricenergy,atthistimemaximumofvoltage

appears

incapacitor.此后即在、構(gòu)成的振蕩回路中發(fā)生電磁振蕩，在某一式中—變壓器的特性阻抗

-transformercharacteristicimpedance若略去截流瞬間電容上所儲存的能量，則Ifomittingtheenergystoredincapacitorsattheclosuremoment.式中—變壓器的特性阻抗若略去截流瞬間電容截流現(xiàn)象通常發(fā)生在電流曲線的下降部分，設(shè)為正值，則相應(yīng)的必為負(fù)值。當(dāng)開關(guān)中突然滅弧時，中的電流不能突變，將繼續(xù)向充電，使電容上的電壓從“”向更大的負(fù)值方向增大，如圖9-9所示。Theclosurephenomenonusuallyoccursinthedeclinepartofcurrentcurve.ispositive,thecorrespondingmustbenegative.Whenthearcextinguishessuddenlyintheswitch,thecurrentcannotmutate,continuingtochargeto,sothatthevoltageonthecapacitorfromthe“"toagreaterincreaseinnegativedirection,asshowninFigure9-9.

截流現(xiàn)象通常發(fā)生在電流曲線的下降部分，設(shè)為正值，則相

此后，在回路中出現(xiàn)衰減性振蕩，其頻率為Sincethen,intheloopattenuationofoscillationappears,itsfrequencyis

此后，在回路中出現(xiàn)衰減性振蕩，其頻率為圖9-9截流前后變壓器上的電壓和電流波形Fig9-9Thetransformervoltageandcurrentwaveformsbeforeandafterclosure圖9-9截流前后變壓器上的電壓和電流波形

以上介紹的是理想化了的切除空載變壓器過電壓的發(fā)展過程，實際過程往往要復(fù)雜得多，斷路器觸頭間會發(fā)生多次電弧重燃。與切除空載線路的情況相反，重燃對降低過電壓是有利因素。變壓器參數(shù)也會影響切空變過電壓的幅值。實際的過電壓將大大低于理想情況下的過電壓。Descriptionaboveistheidealizeddevelopmentofremovingno-loadtransformerover-voltage.Theactualprocessisoftenmuchmorecomplex.Betweencircuitbreakercontactsthearcrenewalwilloccurseveraltimes.Oppositetotheremovalofno-loadlines,renewalisapositivefactortoreduceover-voltage.Transformerparameteralsoaffectstheamplitudeofno-loadvoltage.Theactualover-voltagewouldbesignificantlylowerthantheover-voltageinidealcase.返回以上介紹的是理想化了的切除空載變壓器過電壓的發(fā)9.3.2影響因素和限制措施(Influencingfactorsandrestrictivemeasures)

影響因素及對應(yīng)的限制措施主要有：(Influencefactorsandtherestrictivemeasuresinclude:)1、斷路器性能(CircuitBreakerPerformance)

切斷小電流的電弧時性能越好的斷路器，其切空變過電壓的幅值越高。Whencuttingoffthearcofsmallcurrent,thebettertheperformancethecircuitbreakersis,thehigheramplitudeofno-loadvoltageis.9.3.2影響因素和限制措施影響因素及對應(yīng)的限制措施主要有2、變壓器特性TransformerCharacteristics

優(yōu)質(zhì)導(dǎo)磁材料應(yīng)用日益廣泛，變壓器的激磁電流減小很多；Becausetheincreasinglywidespreadapplicationofhigh-qualitymagneticmaterials,thetransformermagnetizingcurrentisreducedalot;

變壓器繞組改用糾結(jié)式繞法以及增加靜電屏蔽等措施，使過電壓有所降低。Kink-typeoftransformerwindingsandincreasingtheelectrostaticshieldingandothermeasuresenableover-voltagetodecrease.2、變壓器特性TransformerCharacter3、采用避雷器保護(hù)Protecting

usingsurgearresters這種過電壓的特點：幅值比較大，持續(xù)時間短、能量小，易受限制。Characteristicsofthisover-voltage:relativelylargeamplitude,shortduration,smallenergy,vulnerabletorestrictions.4、裝設(shè)并聯(lián)電阻Theinstallationofparallelresistor

在斷路器的主觸頭上并聯(lián)一線性或非線性電阻，其限值應(yīng)接近于被切電感的工作激磁阻抗（數(shù)萬歐）。Thecircuitbreaker'smaincontactsareparallelwithalinearornon-linearresistors.Thelimitsshouldbeclosetotheworkofmagnetizinginductanceimpedance(tensofthousandsofEurope).3、采用避雷器保護(hù)Protectingusingsur發(fā)展過程Development影響因素和限制措施Influencingfactorsandrestrictivemeasures斷路器性能CircuitBreakerPerformance

變壓器特性TransformerCharacteristics采用避雷器保護(hù)Protectingusingsurgearrestersto裝設(shè)并聯(lián)電阻Theinstallationofparallelresistance小結(jié)(Summary)

返回（本節(jié)完）發(fā)展過程Development小結(jié)返回（本節(jié)完9.4斷續(xù)電弧接地過電壓Intermittentarcgroundingover-voltage

中性點不接地電網(wǎng)中的單相接地電流(電容電流)較大，接地點的電弧將不能自熄，而以斷續(xù)電弧的形式存在，就會產(chǎn)生另一種嚴(yán)重的操作過電壓——斷續(xù)電弧接地過電壓。Thesingle-phasegroundingcurrentinungroundedpowergrid(capacitivecurrent)islarge.Thenthearcintheplacewillnotself-extinguishandexistintheformofintermittentarcwhichcreatesanotherseriousover-voltage—intermittentarcinggroundingover-voltage.9.4斷續(xù)電弧接地過電壓中性點不接地電網(wǎng)中的單相

斷續(xù)電弧接地過電壓出現(xiàn)在下列三種情況下后果比較嚴(yán)重：Intermittentarcgroundingover-voltageappearinginthefollowingthreecases

willresultinmoreseriousconsequences:系統(tǒng)中有一些弱絕緣的電氣設(shè)備

Thereissomeelectricalequipmentofweakinsulationinsystem設(shè)備絕緣在運行中可能急劇下降

Equipmentinsulationmaysharplydecline設(shè)備絕緣中有某些潛伏性故障

Therearesomelatentfailuresinequipmentinsulation斷續(xù)電弧接地過電壓出現(xiàn)在下列三種情況下后果比較嚴(yán)本節(jié)內(nèi)容

(Thecontentofthissection)9.4.1發(fā)展過程Developmentprocess9.4.2防護(hù)措施Precautionmeasurements

本節(jié)內(nèi)容(Thecontentofthisse

這種過電壓的發(fā)展過程和幅值大小都與熄弧時間有關(guān)。存在兩種熄弧時間：

Thedevelopmentandamplitudeofsuchover-voltagearerelatedwithextinctiontimeofarc.Therearetwoarcblow-outtime:

電弧在過渡過程中的高頻振蕩電流過零時即可熄滅

Arccanextinctwhenhigh-frequencyoscillationisoverzerointhetransitionprocess電弧的熄滅發(fā)生在工頻電流過零的時刻Extinctionofthearcoccursatthepowerfrequencycurrentzero-crossingtime9.4.1發(fā)展過程Developmentprocess這種過電壓的發(fā)展過程和幅值大小都與熄弧時間有關(guān)

下面假定電弧的熄滅發(fā)生在工頻電流過零的時刻，來說明這種過電壓的物理發(fā)展過程：Assumingextinctionofarcoccursatthepowerfrequencycurrentzeromoment.Toillustratethephysicaldevelopmentofthisover-voltage:作如下簡化：Makethefollowingsimplification:1）略去線間電容的影響；Omitthecurrentimpactbetweenlines;2）設(shè)各相導(dǎo)線的對地電容均相等，即C1=C2=C3=C。就可得如圖9-10(a)所示的等值電路。Assumingeachphaseconductorlocatedonthegroundcapacitorsareequal.Thatis,C1=C2=C3=C.EquivalentcircuitisshowninFigure9-10(a).下面假定電弧的熄滅發(fā)生在工頻電流過零的時刻，來圖9-10單相接地故障電路圖和向量圖Fig9-10Single-phasegroundfaultcircuitandvectordiagram

圖9-10單相接地故障電路圖和向量圖AssuminggroundfaultoccursintheA-phasewhenpassesrightlythroughthemagnitudeof.SothatthepotentialAphaseconductorimmediatelybecomeszeroandtheneutralpointpotentialincreasesfromzerotophasevoltage.Thatis,,B,Ctwo-phase-to-groundvoltagesareincreasedtoalinevoltageof,.

設(shè)接地故障發(fā)生于A相，而且是正當(dāng)經(jīng)過幅值時發(fā)生，這樣A相導(dǎo)線的電位立即變?yōu)榱悖行渣c電位由零升至相電壓，即，B、C兩相的對地電壓都升高到線電壓、。Assuminggroundfaultoccursi

如以uA，uB，uC代表三相電源電壓；以u1，u2，u3代表三相導(dǎo)線的對地電壓，即C1、C2、C3上的電壓，則通過分析可得如圖所示的過電壓發(fā)展過程。IfuA,uB,uCstandforthree-phasepowersupplyvoltageandu1,u2,u3areonbehalfofthree-phaseconductorstogroundvoltage,thatis,thevoltageonC1C2,C3,thenbyanalyzingthedevelopmentofover-voltagecanbeshowninfigure.如以uA，uB，uC代表三相電源電壓；以u1，u按工頻電流過零時熄弧的理論分析得出的結(jié)論是：Theconclusionanalyzedbythetheorythatfrequency-currentisextinctwhenoverzerois

1）非故障相上的最大過電壓為3.5倍；

Themaximumover-voltageonthenon-faultphaseis3.5times;2）故障相上的最大過電壓為2.0倍。

Themaximumover-voltageonthefaultphaseis2.0times.

長期以來大量試驗研究表明：故障點電弧在工頻電流過零時和高頻電流過零時熄滅都是可能的。Foralongtime,alargenumberofpilotstudieshaveshownthat:theextinctionoffaultpointarcispossiblewhenthepowerfrequencyarc-currentandhigh-frequencyareoverzero.按工頻電流過零時熄弧的理論分析得出的結(jié)論是：Theconc發(fā)生在大氣中的開放性電弧往往要到工頻電流過零時才能熄滅；在強烈去電離的條件下，電弧往往在高頻電流過零時就能熄滅。Openelectricarcoccurringintheatmospherecanextinguishwhenthepowerfrequencyelectriccurrentisoverzero.Inintenseionizesc