电容器 (5)

1Lecture7PDDetectioninPowerCapacitors电力电容器的局部放电测量2Contents1.PartialDischargeinPowerCapacitors电力电容器中的局部放电2.ParametersandStandard测试参数及相关规程3.ElectricalDetectionofPDinCapacitor电力电容器的局部放电电测法31.PartialDischargeinPowerCapacitors1.1thecharacteristicsofpowercapacitorsInsulationstructureofcapacitors:oil-impregnatedpapers,oil-impregnateddielectricmembraneandtheircombination.绝缘结构：油浸纸，浸渍薄膜及其组合Extremelyhighelectricalfieldstressexistsincapacitorsandpartialdischargesareverypossibletooccurinside.介质工作场强特别高，内部特别容易发生局部放电电力电容器的特点41.2InceptionanddamageofPDinpowercapacitor1.PartialDischargeinPowerCapacitorsU+cbbaadU+cbbaadCBrbrciEdu])([]11[CBdUErbrbiThelifetimeofcapacitorsufferingfromPDdecreasesexponentially.PDisakeyfactorthatresultsinexpandingandincipientfaultofpowercapacitor.在局部放电作用下，寿命是随着电场的增加而呈指数形式下降的局部放电是造成电容器膨胀和早期损坏的一个重要因素52.ParametersandSpecification2.1ParameterstoestimatethePDofcapacitorApparentcharge,qInceptionvoltage,UiTheACvoltageacrossthecapacitoratwhichthedischargemagnitudeexceedsagivenvalueqg.vsCKTnq)1(5vsCqCdRdCkCxAB)1(kdxdvCCCCCnF40xCpCqg3nF40xCpCCqxg10/5.1视在放电量升压过程中，观测到的放电量超过某个规定值时的最低电压Inceptionvoltage(stress):TheACvoltage(stress)acrossthesampleatwhichdischargesstarttooccurwhenthevoltageisincreased.6Extinctionvoltage,Ue降压过程中，观测到放电量低于某个规定值的最高电压值。TheACvoltageacrossthecapacitoratwhichthedischargemagnitudeislessthanthegivenmagnitudeqg.queuiuba30201001020Time(min)q(pC)aisbetterthanb2.ParametersandSpecificationChangeofqwithvoltageapplyingtime放电量随加压时间的变化72.2ProcedureofPDdetection2.ParametersandStandardsU1:pre-appliedVoltage预加电压TypeU1(kV)U2(kV)U3(kV)RequirementNoteShuntcapacitors2.15un,1s1.2un,10min1.5un,10minSeries-connectedcapacitors4.5un,1s1.6un,10minBreakercapacitors1.8un,1s1.1un,10minDuringlast10min,noPDimpulseswithincreasedmagnitudeareobserved.unisworkingvoltage.U1U2U3t1t2t3U2:holdingvoltage保持电压U3:measuringvoltage测量电压8Powersource:sinewave,50Hz,60HzThecapacitancedifferencebeforeandaftertestshouldnotexceedthedifferencecausedbyafuseburningout.Asimulatingsmallcapacitorscanbeusedwhensensitivityorcapacitycouldnotmeetthetestrequirements.2.ParametersandStandards试验电压为正弦波，频率为50或60Hz测试前后测量电容，两次测量值之差不能超过一根熔丝断开的差值如果被试电容器的电容值太大，在整台上不能得到满意的精度或设备容量不够的时候，用模拟的较小电容器进行试验。93.ElectricalDetectionofPDinCapacitorThecapacityofapowercapacitorismuchlargerthantheusualHVequipments.LargecapacityofthepowersourceisrequiredforPDexperimentofcapacitors.3.1PowerSourceandCircuits(1)PowersourceCompensationreactorisusedinseriesorparallelwithCxsothattodecreasethecapacityoftestingtransformerILIcIeLuCuueCurrentsthroughLandCwhilethetwoelementsconnectedinparallelVoltagesacrossLandCwhilethetwoelementsconnectedinseries试验电源及回路电容器的容量比其他普通高压设备大很多，因此所需的试验设备容量也很大采用补偿电抗器与试品串并联的方式满足实验变压器的容量要求10(2)DetectioncircuitsvsCKTnq)1(5vsCqCdRdCkCxAB)1(kdxdvCCCCCe.g.pFCx2001pCqs05.0FCx2002sqpC50Ck↗qs↘Cv↘3.ElectricalDetectionofPDinCapacitorsensitivity11ABalanceddetectioncircuitisrecommended3.ElectricalDetectionofPDinCapacitorThestraightdetectioncircuitsmaybeused.Inordertoobtainhighsensitivity,thecouplingcapacitorshouldbeatleastaslargeasthesample.Asecondsampleisusedasthecouplingcapacitor,Ck=Cx.CxZdZmeCk=CxoACx2ZmeoACx1Zd1Zd2采用直接测量回路，并用另外一个试品作为耦合电容使用平衡检测回路12(2)Theinfluenceofinternalinductance3.2Someproblemsneedtobenoticed(1)RequirementsofdetectionimpedancesThecapacitancerangeofpowercapacitorsislargerthanthatofmanyotherHVequipments，severaldetectionimpedancesareneededtomatchthecapacitorsamples,sothattogettheproperfrequency-bandandsensitivity.3.ElectricalDetectionofPDinCapacitor电力电容器的电容量比其它高压设备电容量的变化范围大,需要准备多个检测阻抗，以匹配不同电容量大小的试品.以便得到合适的检测频带和灵敏度。Detectionimpedancesisrequiredtowithstandlargecurrent.检测阻抗需要承受较大的电容电流对检测阻抗的要求注意的问题)1(kdxdvCCCCC))/((kxkxtCCCCCdC13(2)Connectiontypesofcapacitorelementsinfluencedetectionresults.3.ElectricalDetectionofPDinCapacitor电容器元件的连接形式会影响检测结果。xCxCxCxCdURdCdCkxU)1(kdxdadCCCCqUxCxCxCxCxU'dURdCdCk)'1('kdxdadCCCCqU11'nCCnCCCxkxkk)()1(11'1'dkxdkkdkdddCCCnCCCCCCUUK14(3)TheinfluenceofinternalinductancePowercapacitorisnotpurecapacitance.Theinternalinductancecomesfrom:internalleads,leadingoutwires,capacitorelementsconnectinginseriesorparallel.L≈0.1~0.3μH电力电容器不是纯电容设备，内部电感来自于：内部引线，引出线以及以串并联连接的各个电容器元件本身。L≈0.1~0.3μHInfluencesonPDdetection:resultinmeasurementerrorCalibrationresults3.ElectricalDetectionofPDinCapacitor内部电感的影响decreasethesensitivity,resolution测量结果误差降低灵敏度，分辨率错误的标定结果15TheEnd