電氣外文翻譯

翻譯部分中文譯文中壓補償電網(wǎng)間歇性接地故障檢測摘要-從波蘭中壓電力配網(wǎng)獲得的經(jīng)驗表明應(yīng)用于間歇性接地故障的故障點定位判據(jù)是不可靠的，這主要是因為不穩(wěn)定性，還有低功率水平的測量信號常常衰減到了保護動作值以下。本文提出來一種新的基于小波分析的自適應(yīng)算法，這種算法能夠動態(tài)檢測間歇性接地故障中的測量信號。本算法利用EMTP程序包產(chǎn)生的信號進行分析驗證。1、前言一般來說，波蘭的中壓配網(wǎng)采用中性點經(jīng)消弧線圈接地的方式。經(jīng)查證，農(nóng)村地區(qū)線路大部分是架空線路。這種網(wǎng)絡(luò)的特征是90%的線路故障是接地故障。這主要因為故障點較高的過渡電阻和一些天氣因素如閃電，狂風，高溫和低溫等的影響，這些因素都將導(dǎo)致傳輸線路的老化，破裂，從而導(dǎo)致接地故障的發(fā)生。由于上述接地故障特征的干擾，使得檢測定位故障點也比較困難。主要討論如下故障類型：高阻抗%接地故障；進線側(cè)線路短路過程中的閃落；周期的和非周期發(fā)生的故障；一個實際的故障可以表現(xiàn)出上述所有特征。本文所做的分析僅限于間歇性接地故障過程中的自動保護單元。為了評估保護的運行性能，在故障過程中測量信號的特征和等級均是被標定了的。電網(wǎng)發(fā)生間歇性接地時最重要的信號指示是零序電壓分量，該值可以通過計算瞬時相電壓值求得。故障定位的判據(jù)如下：零序電流分量，I;0零序電壓分量U0，零序電流分量10計算所得零序功率；零序電流和零序電壓分量的相位角：零序?qū)Ъ{y，或者它的實部氣，和虛部氣；然而，上述判據(jù)值在間歇性接地故障發(fā)生時就不一定準確了。2、網(wǎng)絡(luò)模型為了模擬和研究間歇型接地故障現(xiàn)象，本文給出了一種典型的中壓對稱網(wǎng)絡(luò)。網(wǎng)絡(luò)模型如下圖所示：

Mm.,Fig.lMediumvoltage-networkschenie故障采用EMTP/ATP程序仿真，電網(wǎng)的仿真參數(shù)設(shè)置如下表所示:Mm.,15Kv模擬電網(wǎng)參數(shù)電網(wǎng)電容電流I0101.3A故障線路電容電流I0110.6A補償度+15%過渡電阻RF2在上述模型中，假定故障線路接地電容電流為10.6A，負載功率為150kW。本文分別分析了以下故障類型：A、永久性故障；B、持續(xù)時間和中斷時間均為10ms的間歇性接地故障；C、持續(xù)時間為10ms，中斷時間為100ms的間歇性接地故障；D、持續(xù)時間為50ms，中斷時間為50ms的間歇性接地故障；所有的故障類型均在線路1的初始端進行模擬，即靠近母線側(cè)。記錄如下數(shù)值:零序電壓分量U0，故障線路零序電流分量101和非故障線路零序電流分量102。3、實驗結(jié)一導(dǎo)納判據(jù)在第一節(jié)強調(diào)的保護判據(jù)里面，對于比較復(fù)雜的故障如間歇性接地故障，最有效的判據(jù)是零序?qū)Ъ{K，或者它的實部G，和虛部B為了實現(xiàn)導(dǎo)納型故障保護，使用了幅值比較器（見圖2中CA1,CA2）。簡單模型中，輸入信號按照如下規(guī)則進行比較：TOC\o"1-5"\h\z*=匕匕■；（1）52=kU0；（2）七=kU0；（3）其中，k，k，k為測量過程中處理輸入信號的對應(yīng)系數(shù)。123Fig.2.Admittance-typeearthfaultprotecticn-Fig.2.Admittance-typeearthfaultprotecticn-equivalentschemeCAI^CA2接地故障保護反應(yīng)于零序?qū)Ъ{模塊信號土和土比較單元。比較發(fā)生在幅值比較器CA1，當滿足下式：§<52；（4）第i條線路保護動作。這也意味著第i條線路的保護動作區(qū)域由如下導(dǎo)納向量y=n>、；（5）01Uk02所決定。圖3表示了這種保護的啟動響應(yīng)，它僅僅是一個普通的同樣包含復(fù)導(dǎo)納平面所有部分的譜圖。保護動作輔助部分是適當水平的零序電壓分量。本方案中，啟動單元是比較器CA2，CA2中信號53和啟動信號53依據(jù)下式比較：S3=kU0>54；（6）其中54是按照根據(jù)接地故障時和正常電網(wǎng)的不同設(shè)定的初始值。

^Jpeuiriiigcharacren^ricFig.3.Srart-uyresponseofrheadmitrance-T^peearth-faulprotection圖4中表示了線路1發(fā)生永久性故障時的故障線路零序電流分量101和非故障線路I，零序電壓分量U，故障線路零序?qū)Ъ{K，非故障線路零序?qū)Ъ{K。0200102Fig.4Conriiivousearthfault(Atype)-mline1測得的故障線路零序?qū)Ъ{將高于非故障線路。依據(jù)判據(jù)4分辨故障線路不會造成判斷問題。類似的，間歇性接地故障截止頻率高，相應(yīng)的幅值如圖5所示。由于故障發(fā)生時暫態(tài)的延遲作用，零序電壓仍為發(fā)生永久故障時電壓值，并且測得故障線路的導(dǎo)納將持續(xù)明顯高于非故障線路。(VJyCVIM(WM-m.rm》#ESWSHIN.Rys.5.Lnt^ruurteutearthfaul(B-type)mlineLHine(niF電6BLremuttentearrhfault(C-type)inline1Fig.7LttemiitTenrearrlifault（D-rype）inlineL短路線路中斷時間比較長時（如C型和D型故障）描述比較困難。該類故障運行曲線如圖6和圖7所示。故障持續(xù)期間，零序電壓分量（對應(yīng)于保護啟動信號七）保持較大值，再考慮故障發(fā)生后立即出現(xiàn)的比較小的衰減的暫態(tài)電壓分量，這就意味著檢測故障不難。然而，如何描述故障線路卻有點問題。這是因為暫態(tài)過程中，故障點周期性的電弧引燃，故障線路的導(dǎo)納相應(yīng)于非故障線路會周期性的下降。C型和D型故障均是這種情況，此時，相關(guān)的導(dǎo)納判據(jù)也是不正確的。利用小波展開將會是一個好的選擇，特別是對于多分辨率的信號分解方面。4、多分辨率小波分析小波分析作為一種主要工具應(yīng)用在測量信號的多分辨率分解方面，這主要通過多級的小波補充濾波（高通和低通的定比函數(shù)）實現(xiàn)的。程序?qū)崿F(xiàn)分解算法為Mallat法則。創(chuàng)造多分辨率信號表示的迭代處理過程可以用圖8所示的小波信號分解樹演示。任何一步迭代過程，所分析均是被過濾過的。迭代的階次也不是無限制的，如圖8中，n為假定的階次。每一個迭代結(jié)果包含兩部分：稱作Q的高頻分量，它在連續(xù)迭代步驟中不再過濾；用于分析初始信號S的低頻分量A，ii稱作應(yīng)用近似值。因此，信號分解過程有一種多級迭代過程實現(xiàn)低通濾波，并且連續(xù)近似和連續(xù)分解過程相反。選擇用于信號分析的母小波如圖5,6,7所示，當用于分析信號頻譜時，光滑的小波分解信號較好，因為它們有較好的頻域局部性，尖形的小波有較好的時域局部性。綜觀大多小波類型，作者得出，Haar小波的特性能夠更好的滿足本方案應(yīng)用要求，因為它的保護中實時計算速度快，區(qū)分度好?；镜腍arr小波按照如下定義：…11(0jfJ2)1(7)w(t)={-1(；<t<1)20(其它)(7)小波元素系列如下：中(t)=2-m/2中(2-mt-n)m,n=…，-2,-1,0,1,2,…(8)函數(shù)wmn在所提議應(yīng)用中的優(yōu)點主要是通過任意函數(shù)中斷的精確定位，可以獲得時域的無限精確定位（尤其對于迭代步驟，見圖5和圖6）,函數(shù)的分解通過小波列定義。Haar小波縮放函數(shù)滿足如下關(guān)系：11(0<t<1)（9）'(t)=〔0(其它)（9）眾所周知，多級分解是以高速計算性能為代價的。在一個簡單的Haar小波應(yīng)用實例中，每一步分解均限于計算平均值（低通）或者微分值（高通）。平均值是一種粗略的表示（近似），而微分值是一種精確的表示。7■-T，｝…||I二I[A11Fig.?Signalwaveletdecompositiontrre（^T））5、間歇性接地故障中測量信號的多級分解和故障線路描述為了更好的描述接地故障線路，本文使用第四節(jié)所討論的測量信號分解的迭代方法。本文分析了故障線路零序電流101,非故障線路零序電流102。圖9~14展示了B,C,D型間歇，性故障時獲得的信號和六級分解的情況。圖示結(jié)果通過基本Haar小波變換獲得，采樣頻率為10kHz。圖中，信號的頻率特征不明顯，但幅值和時間位置卻很明顯，在的，d1,d2,d3級中即時相位變換現(xiàn)象尤其明顯。在更高級的分解中，如d4,d5,d6中，相位變換現(xiàn)象就不那么明顯了（非故障線路）或者成為主要成分了（故障線路）。這種現(xiàn)象可以作為區(qū)別故障線路和非故障線路的依據(jù)。信號中斷時的尖形突出將會導(dǎo)致信號平均值遠低于信號的峰值。

在d4,d5,d6級中包含高頻成分，平均值絕對值、）的執(zhí)行比例和在寬度N的數(shù)據(jù)窗中計算得的第K個值滿足如下關(guān)系：i=NEabs[i（k-n）]；n（10）間歇性接地故障中短路線路的描述通過比較C和起始值二,實現(xiàn)，C代表瞬時電流絕對值與平均值的比值。C=abs(i(C=abs(i(k))>C；（11）一L(k)''.ofcumenlB-type-intermitXZ7T二二二XZ7T二二二Time,ms二A；0.25-r-a6o「八一■025十-

0R.ys.11.Five-leAreldecompositionofcuneiitsignal.damagedline,

C-typemteritiittetttfault1-rTOC\o"1-5"\h\z0,5丁二「了—；d40^fiR^^^j^******^^******^^**^-0,54\0.51—二；二[一二二—n—!d5o-□5【!1了—-.：[::=d6o!a^aa^amv^'/J^WJ叫叫v叫1q%A(v^1【!0251a6o^v/Y/x/^^^x/Y/xzNz^x^zx/x/vzx^^x/y/x^-0J5X1\o"CurrentDocument"0Time,ms4"Fig.12Five-LeveldecompositionofcurrentsignalZ02；undamagedline.C-typeintermittentfault-0.25+T0Time,ms。釗Rys.13.Five-leveldecctnposirionofcurrentsigiiaLJq2；damagedlineD-1ypeinteTtnitteutfault證實當保護滿足式（11）條件時，斷路器會斷開，零序電壓分量（OS1=1）接地故障仍然存在，任何切斷保護導(dǎo)納部分（OS2=0）脈沖（OS）均不發(fā)出

證實Rys.14.Five-leveldecompositionofcurrent2d‘：undamagedline.Fig?l5.DiscrimuLationalgoritliwforlinewithmteinjittenifeiilt（csroiLudCPAC}圖16中，表示了一種自適應(yīng)接地故障保護的方案框圖，它是對傳統(tǒng)導(dǎo)納保護（見圖2）的延伸?；镜难a充模塊有：測量信號多級分解模塊WD模塊，實現(xiàn)線路描述算法的PAC比較器（峰值-均值比較器）（見圖15）。Rys.1ft.Adaptiveearthfaultprctectiou—blockscheme鑒于傳統(tǒng)保護判據(jù)的不可靠性，上述保護的邏輯結(jié)構(gòu)中，WD模塊和PAC模塊增強了保護運行過程中故障消除的能力和可靠性。6、結(jié)語本文間歇性接地故障實驗中測得信號U0和10表明，傳統(tǒng)保護設(shè)備在確定這類故障和鑒別故障線路方面存在一些問題。如果故障間中斷時間超過10ms，檢測困難也會增加。因為這種中斷也會在不平衡配網(wǎng)中出現(xiàn)，一些接地故障時保護不動作情況自然也會出現(xiàn)。因此，基于消除此類問題的新的保護判據(jù)也正在研究當中。經(jīng)過分析間歇性接地故障實驗，我們很容易得出，多級小波分解能夠甄別被保護線路的信號特征。本文所有例子表明，故障線路和非故障線路原始信號在初級分解（d1，d2，d3）中干擾比較明顯。而在高級分解之中，故障和非故障線路的譜圖明顯不同，這也促進了分辨故障線路，排除故障。7、參考文獻S.Mallat,"ATheoryformultiresolutionsignaldecomposition:thewaveletrepresentation",IEEETrans.OnPatternAnalysisandMachineIntelligence,Vol11,No7,1989,pp.674-693.Shyh-JierHuang,Cheng-TaoHsieh,Ching-LienHuang,"Applicationofwaveletstoclassifypowersystemdisturbances"ElectricalPowerandEnergySystem,47,1998,pp.87-93.O.Chilard.,L.Morel.,D.Renon.,"Compensatedgroundedmediumvoltagenetworkprotectionagainstresistivephasetogroundfaults",CIRED,Nice1999AburA.,MagnanoF.H.,"Useoftimedelaysbetweenmodalcomponentsinwaveletbasedfaultlocation",ElectricalPowerandEnergySystem,22,2000,pp.397-403LobosT.,RezmerJ.,"Wavelettransformsforreal-timeestimationoftransmissionlineimpedanceundertransientconditions",ElectricalEngineering,84,2002,pp.63-70.D.Chanda,N.K.Kishora,A.K.Sinha,"Awaveletmultiresolutionanalysisforlocationoffaultsontransmissionlines",ElectricalPowerandEnergySystem,25,2003,pp.59-69.8、作者簡介JozefLoren，生于1949年，波蘭的小鎮(zhèn)Jarocin，獲得波茲南科技大學電氣工程專業(yè)的碩士和博士學位。目前，職稱為副教授，擔任電氣電力工程學會主任。從事電力系統(tǒng)繼電保護領(lǐng)域工作，主要研究電網(wǎng)保護判據(jù)、無功補償、中壓配網(wǎng)中性點運行、接地保護、電流沖擊保護等方面。KazimierzMusierowicz，生于1943年，于1969年畢業(yè)于弗羅茨瓦夫科技大學電氣工程專業(yè)，獲得波茲南科技大學碩士學位，現(xiàn)為該校講師和研究員。從事電力系統(tǒng)繼電保護和數(shù)字信號處理領(lǐng)域的研究工作。AndrzejKwapisz，生于1971年，波蘭的小鎮(zhèn)Szczecinek，獲得波茲南科技大學碩士學位。目前為該校研究員。主要從事電力系統(tǒng)數(shù)字技術(shù)，計算機輔助電力系統(tǒng)分析，暫態(tài)和穩(wěn)態(tài)電力系統(tǒng)仿真，繼電器開發(fā)標準等領(lǐng)域研究工作。英文原文DetectionoftheIntermittentEarthFaults

inCompensatedMVNetworkJozefLorenc*/,KazimierzMusierowicz*/,AndrzejKwapisz*/Abstract-TheexperienceacquiredfromthePolishmediumvoltagepowerdistributionnetworksshowstheunreliabilityofthelocalizationcriterionsappliedtotheintermittentearthfaults.Itresultsfromthelackofstabilityandlowpowerlevelofthemeasuringsignalsfallingoftendownbelowtheprotection’sstart-uplevel.Inthepaper,anewadaptivealgorithmbasedonthewaveletanalysisenablingdetectionofspecificdynamicsofthemeasuringsignalduringintermittentearthfaultsispresented.ThealgorithmwasanalyzedutilizingthesignalsgeneratedintheEMTPprogrampackage.INTRODUCTIONIngeneral,theMVdistributionnetworksinPolandoperatewiththeneutralpointgroundedthroughthecoiltocompensatethecapacitiveshortcircuitcurrenttotheearth.Itrefersmainlytotheruralareanetworkswherethelinesaretheoverheadones.Suchnetworksarecharacterizedbylargenumberoftheearthfaultsexceeding90%ofallrecordedfaults.Duetotherelativelyhighcrossresistanceatthedefecfslocation(RF)aswellastotheeffectsoftheweatherphenomenasuchasdischarges,gustsofwind,highandlowtemperaturesresultingintheruptureofthelineconductorscontinuity,theearthfaultsoccur.Characteristicsofthesefaultsmakesimpossiblethedetectionandlocalizationofsuchdisturbance[3].Thefollowingfaulttypescanbeencounteredtothediscussedfaultsgroup:-resistancefaultsofhighcrossresistance,R,-breakinthelivewireshortcircuitonthereceiverside,-faultsbeingbrokencyclicallyandnon-cyclically.Anactualfaultcanshoweitheroneorallofthelistedfeatures.Inthepaper,theanalysisislimitedtotheautomaticprotectiveunitsoperationduringintermittentfaults.Toassesstheprotection’soperability,thelevelsandfeaturesofmeasuringsignalswhichcanoccurduringthefaultaretobeidentified.Themostimportantsignalindicatingoccurrenceoftheintermittentearthfaultinthenetworkisazero-voltagecomponentthevaluesofwhichisoftenfoundbyaddingtheinstantvaluesofphasevoltages.Thecriterionvalueofthefaultlocalizationcanbe:-zerocurrentcomponent,I0-powerofthezerocurrentcomponent,I,andzerovoltagecomponent,U,-phaseshiftanglebetweenthezerocurrentandvoltagecomponents,-zeroadmittancecomponent,Y,oritscomponents:activeGorreactive.BHowever,thecriterionvaluesaslistedaboveareoftenunreliablewhenthe

intermittentearthfaultoccurs.MODELOFNETWORKFormodelingandstudiesoftheearthfaultphenomenaaccompanyingtheintermittentearthfaults,atypicalmediumvoltagebalancednetworkhasbeenchosen.TheschemeofmodelednetworkisshowninFig.1.mW,Fig.lMediumvoltage-networkschememW,ThefaultsweremodeledandsimulatedusingtheEMTP/ATPprogrampackage.ChosenparametersofnetworkassumedforsimulationpurposesareshowninTable1.TABLE1MODELLED15KVNETWORKPARAMETERSNetworkcapacitycurrentI0101,3AFaultlinecapacitycurrentI0110,6ADecompensationlevel+15%CrossresistanceRF2WInthemodeltheassumptionwasmadethatthefaultsoccurinalinewithto-ground-capacitivecurrentof10.6Aandamoderatedpowerloadof150kW.Thefollowingfaulttypeshavebeenconsidered:-A-type-continuousfault,-B-ype-intermittentfaultoftsc=10msdurationtime,tp=10mspausetime,-C-type-intermittentfaultoftsc=10msdurationtime,tp=100mspausetime,-D-type-intermittentfaultoftsc=50msdurationtime,tp=50mspausetime.Allfaultshavebeenmodelledatthebeginningoftheline1,adjacenttothebusbars.Thefollowingmagnitudeshavebeenregistered:networkvoltagezerocomponent,U,aswellasthezerocomponentcurrentofthedamagedline,I,andthatoftheundamagedline,I.RESULTSOFEXPERIMENTS-ADMITTANCECRITERIONAmongthecriterionvaluesforprotectionsasspecifiedinsection1,forthe‘difficult’faultcasessuchasintermittentearthones,themosteffectiveiseithertheadmittanceY0oroneofitscomponents:conductanceGorsusceptanceB.Toimplementtheadmittance-typeearthfaultprotections,theamplitudecomparators(CA1,CA2inFig2)areused.Inthesimplestcase,theinputsignalscreatedaccordingtothefollowingrulesarebeingcompared:TOC\o"1-5"\h\z*=々。-；(1)七=kU0；(2)§=kUo；(3)Thek,kandkcoefficientsdeterminetheproportionalityoftheinputsignalprocessingintheprocessinginthemeasuringpaths.Fig.2.Admittance-typeearthfiultprotection-equivalentschemeTheearthfaultprotectionrespondingtothezeroadmittancemodulecomparestheS1andS2signals.ThecomparisontakesplacewithintheamplitudecomparatorCAl.Theprotectioninthei-thlineactswhenTOC\o"1-5"\h\z§<S2;(4)Itmeansthattheoperationareaofprotectionlocatedinthei-thlineisdeterminedbytheendsofadmittancevectorsofvaluesmeetingthecondition:Y=匕>、;(5)01Uk02InFig.3,thestart-upresponseofsuchaprotectionisshown.Itisaplain-admittancecurveincludingequallyallquartersofthecomplexadmittanceplane.Supplementaryclauseoftheprotectionoperationisaproperlevelofvoltagezerocomponent.Insuchasolution,thestart-upunitistheamplitudecomparatorCA2inwhichtheS3signalleveliscomparedtothatoftheS4start-upsignallevel,accordingthetheclause:S3=kU0>S4；(6)wheretheS4isthepresetstart-upvalueduetowhichtheearthfaultcanbedifferentiatedfromthenormalnetworkoperation.F〔_g-3一Start-upresponseoftheadmitrance-r^peearth-faulprotectionInFig.4,thecurrentzerocomponentsinthedamagedline,I,andintheundamagedline,I,voltagezerocomponentUaswellaszero-admittancesinthedamagedline,Y,andundamagedlineY,duringcontinuousfault(A-type)inline1arepresented.Tini-e(nit)Fig.4Tini-e(nit)Fig.4Conriuvouseaithfault(A-type}inline1Thezeroadmittancemeasuredinthedamagedlineissome-foldhigherthanthatintheundamagedline.Discriminationofdamagedlineaccordingtocriterion(4)shouldnotposetheproblems.Similarcaseisforanintermittentfaultofrelativelyhighinterruptionfrequency(B-type),thecorrespondingrunsofnalysedmagnitudesareshowninFig.5.Afterdecayofthetransientstateresultingfromthefaultoccurrence,thezerovoltageremainsattheleveladjacenttohevoltageduringthecontinuousfault,andtheadmittancemeasuredinthedamagedlineisallthetimeevidentlyhigherthantheadmittancemeasuredintheundamagedline.rv.)M--1s■普■■=》liine(ms}Rys5Interiiutteutearthfaul(B-type)inline11.-.-=Vrv.)M--1s■普■■=》liine(ms}Rys5Interiiutteutearthfaul(B-type)inline11.-.-=V重密M號，EefflJ=mp<3=O>Tini-eJwouli-InnFig.6IcLTermirt<ntearrhfauh(C-type)inline1Adiscriminationoftheshort-circuitedlineincasewhenthepausebetweensuccessivefaultsisrelativelylong(longtimetp-CandDtypes)canbemoredifficult.Therunsrelatedtosuchfaultsareshowninfigures6and7.Duringentiredurationoffault,thevoltagezerocomponent(towhichthestart-upsignalS3isproportional)remainsatthehighlevel;itmeansthatthefaultdetectionshouldnotbedifficultduetotherelativelylowattenuationofthevoltagetransientsafterinstantaneousdisappearingofthefault.However,theproblemscouldarisewithdamagedlinediscrimination.Duetothefeaturesofthetransientprocessinthenetworkresultingfromthecyclicarcignitionsinthefaultlocation,thedamagedlineadmittancefallscyclicallydowntotheundamagedlineadmittancelevel.ItreferstoboththeC-typeandD-typefaults.Insuchacase,animproperoperationoftheadmittancecriterion-relatedprotectioncanbeexpected.Betteropportunitiesopenwhenusingthewaveletexpansions[2],[4],[5],especiallythemulti-resolutiondecomposition[6]ofthemeasuringsignals(WD).MULTI-RESOLUTIONWAVELETANALYSISAmaintoolofthewaveletanalysisintheproposedapplicationisthemulti-resolutiondecompositionofmeasuringsignalsrealizedbythemultistagesetofthewaveletcomplementaryfilters(high-passwaveletsandlow-passscalingfunctions).ThecalculatingprocedureleadingtothedecompositioniscalledtheMallatalgorithm[1].Theiterationprocessofcreatingthemulti-resolutionsignalrepresentationcanbepresentedintheformofthewaveletsignaldecompositiontreeasshowninFig.8.Atanyiterativestep,theanalysedsignalisfiltered.Thenumberofiterativestepsisunlimited;inFig.8,nstepshavebeenassumed.Eachiterationresultsinboth:thehigh-frequencycomponentcalledadetail(Di)whichisnomorefilteredduringsuccessiveiterativesteps,andthelow-frequencycomponent(Ai)ofanalysedoriginalsignalS,calledanapproximation.Thus,thesignaldecompositionprocesshasaformofthemultileveliterativeprocesscarriedoutonthelow-passfiltrationchannel,andthesuccessiveapproximationsaresubjecttothesuccessivedecomposition.Whenchoosingthemotherwaveletforanalysisofmeasuringsignalsshowninfigures5,6and7,theknownrulehasbeentakenintoaccountthe‘smooth-shape’wavelets(theMorlet'swavelet,forexample)areofbetterresolutionwhenanalysingthesignalfrequencyspectrum,i.e.theyhavebetterlocalizationoffrequencycomponentsalongthefrequencyaxis,whilethediscontinuously-shapedwavelets(theS^r'swavelet,forexample)havebetterresolutionalongthetimeaxis.Referringtotheoverviewofpropertiesofmanywaveletstypes,theAuthorsdrewaconclusionthattheHaar’swavelet’spropertiesmeetinthebestwaytherequirementsoftheconsideredapplication,regardingboththemetrologicalaspectsasthespeedofreal-timecalculationscarriedoutinprotections.ThebasicHaar’swaveletisdefinedasfollows:f11(0JtJ2)1W(t)={—1(—JtJ1)(7)20(其它)andgeneratesasetofwaveletswithelementsas中(t)=2-m/2中(2-mt—n)m,n=…，-2,-1,0,1,2,…(8)Advantageoftheymnfunctioninproposedapplicationistheirgoodlocalizationasforaninfinitelypreciselocalizationintimeisobtainedenablingarbitraryaccuracy

oflocalizationofthefunctiondiscontinuity(especiallythatofthestep-seeFigures5and6),thefunctionexpansionbeingdefinedregardingtheHaar'swaveletset.TheHaar’sscalingfunctionisgivenbyrelationship:11(0<t<1)(9)"')」0(其它)(9)Presentedrealizationofmeasuringsignalsmulti-leveldecompositionischaracterizedbyhighcalculationefficiency.InresultofapplicationofasimpleHaar’swavelet,decompositionateachlevelislimitedtocalculationoftheaveragevalue(low-passfilter)orofadifference(highpassfilter).Theaveragevalueisaroughrepresentation(approximation)whilethedifferenceisapreciserepresentation(adetail).Fig.8SignalwavelerdecQinpositicntree(WD}DECOMPOSITIONOFMEASURINGSIGNALSANDDAMAGEDLINEDISCRIMINATIONDURINGINTERMITTENTEARTHFAULTSFig.8SignalwavelerdecQinpositicntree(WD}Todiscriminatethelineinwhichtheearthfaultoccurred,theiterativemethodofmeasuringsignalsdecomposition(WD)presentedinsectionIVwasapplied.Thezerocurrentcomponentmeasuredintheshort-circuitedline,701,andhealthyline,I02,havebeenanalysed.Infigures9through14,thesix-leveldecompositionofsignalsobtainedforconsideredB-C-andD-typeintermittentfaultsareshown.ThereportedresultshavebeenobtainedusingthebasicHaar’swavelet,atsamplingfrequencyof10kHz.Infigures,thecharacteristicfeaturesofsignalinvariousfrequencyranges,theiramplitudesandpositiononthetimeaxisareevident.attheinstantscorrespondingtothecommutationphenomenaisespeciallyvisibleatthed1,d2andd3levels.Athigherdecompositionlevels,d4,d5,d6,localizationduringcommutationphenomenabecomeeitherlessvisible(intheundamagedline)ordominating(inthedamagedline).Suchafactcanformabasisforthedamagedlinediscriminationi.e.fordistinctionofthelatterfromtheundamagedone.Occurrenceofevident‘spikes’atthesignal’sdiscontinuityinstantsleadstothesignalaveragevaluemuchlowerthanthepeakvalue.

Atthed4,d5andd6levelsalongwiththehighfrequencycomponents,arunproportionaltotheabsoluteaveragevalue(i),thek-thvalueofwhichcalculatedintheMwidthwindowcanbefoundfromtherelationship:i=N￡abs[i(k-n)]；n(10)ispresented.Itisassumedthattheshortedline’sdiscriminationduringtheintermittentearthiscarriedoutbycomparingtheCratiooftheabsoluteinstantaneousvalueandabsoluteaveragevaluetothestart-upvalueoftheCrratio:C=abs(i(k))>C；TOC\o"1-5"\h\z一L(k)r'(11)\o"CurrentDocument"1i-I□LAjAAAAzVAjACjA八八八jAZjA八zm/II_]_L一|觸A停X，?g*m”■卜n”?”，MM打d21110；-片-***?A**，PAp，*■食,*■?■**(IjStopd611——--二二二d60訕岫型nW曾沖加叫心虬叫MpgWgk妙ma6：?0Time,ms遍Pig.10.Five-leveldecompositictiofcumentsignal,Undamagedlin^3B-typemreimineutfarlrd6o-i?015十且1oTime,ms440R.ys.11.Five-leveldecompositionofcurrentsignal.Z02；damagedline,C-typeuiterminentfaultTOC\o"1-5"\h\z1y-10.5t1di?444-~!■0j5'(J20+!d3o!+.??‘*-...?+■■?.?.??.，-1」>0,5r丁二「了1d40-0?5j10.5i：：；：[；；：-二二[T；ij二二JJiUli(15o創(chuàng)神網(wǎng)f郵伸冊0聲-j'i—m(16o!JJiUli-1】!\o"CurrentDocument"0.25110,25110一?440vlune?msFig.12Five-leveldecompositionofcurrentsignal,Z02：undamagedlineC?typeintermittentfaultRys.L3.Five-leveldecompo^iiioncfcmreatsignal.7o2；damagedline,D-typeluterauTtentfhuhWhentheprotectionmeetsthecondition(11),thebreakerwillopenprovidedthatthezerovoltagecomponent,(OS1=1),provingtheexistenceoftheearthfaultstillremains,andanypulse(OS)switchingofftheadmittancepartofprotection(OS2=0)wasnotsentout.Thealgorithmrepresentingthedescribedideaofdiscriminationofthelinetouchedbyanintermittentfaulttoground(PAC)isshowninFig.15111o0卜/VVV\/\yVVVWW\AA/WVvidl0,ot^-0,51l-rd2of-i-1Td3o：f~^-1XTOC\o"1-5"\h\zwh.-05【」05丁—二、[二(15°?0就d6o.1【!\o"CurrentDocument"°%Time,ms")Rys.14.Five-le\-eldecompositionofcuirentsignal.I02；undamagedline.D-typeintennitreatfaultInFig.16,theblockschemeofanadaptiveearthfaultprotectionbeinganextensionoftheconventionaladmittancetypeprotection(seeFig.2)ispresented.Basicsupplementaryblocksare:WDblockinwhichthemulti-leveldecompositionofneasuringsignalstakesplace,andthePACcomparator(peak-averagecomparator)inwhichthelinediscriminationalgorithmisimplemented(seeFig.15).Rys-.16.AdaptiveuetrrhfaultpioTectioii一block5-ch^meDuetothelogicstructureofprotection,theWDandPACblocksenhancefunctionalityandreliabilityofthefaultseliminationwheretheprotectionsoperatingaccordingtotheclassiccriterionsareunreliable.FINALREMARKSReportedexamplesoftheU0andI0measuringsignalsduringtheintermittentearthfaultsshowthatdetectionofsuchfaultsaswellasidentificationofdamagedlinecanposeproblemstotheconventionalearthfaultprotectingdevices.Thedifficultiesarehigherwhentheinnerpauseduringthefaultexceedstensofmilliseconds.Assuchpausescanoccurinthebalancedmediumvoltagedistributionnetworks,anumberofnon-brokenoffearthfaultsshouldbeexpected.Therefore,newprotectivecriterionseliminatingsuchatroublearetobesearched.Havinganalysedtheexamplesofintermittentfaultsitcanbeeasilyperceivedthatthemultilevelwaveletdecompositionenablestoseparatethesignalfeaturestypicalfortheprotectedlineconditions.Allreportedexampleshaveshownthatthedisturbanceoftheoriginalsignalappearsespeciallyevidentatinitialdecompositionlevels(d1,d2,d3)forthesignalscomingfromboththedamagedl