高电压技术第2版 吴广宁4.3

4.3局部放电的测量4.3Measurementofpartialdischarge当电气设备内部绝缘发生局部放电时，将伴随着出现许多现象。有些属于电的，例如电脉冲、介质损耗的增大和电磁波辐射;有些属于非电的，如光、热、噪音、气体压力的变化和化学变化。这些现象都可以用来判断局部放电是否存在，因此的也可以分为电的和非电的两类。Wheninternalinsulationofelectricequipmentproducespartialdischarge,itwillaccompanyseveralphenomenon.Somephenomenonbelongtoelectricfield,suchaselectricimpulse,dielectriclossandelectromagneticradiation;othersarenon-electricfield,suchasthechangoflight,heat,noise,gaspressureandalsochemicalchanges.Thesephenomenoncanbeusedtojudgetheexistenceorabsenceofpartialdischarge.Inconclusion,detectionmethodscanbedividedintoelectricandnon-electrictwotypes.目前得到广泛应用而且比较成功的方法是电的方法，即测量绝缘中的气隙发生放电时的电脉冲。它不仅可以判断局部放电的有无，还可以判定放电的强弱。Recently,electricmeasurementisusedwidelyandsuccessfullyfordetectingpartialdischarge,thatismeasuringelectricimpulseaccompaniedwiththeair-gapdischarge.Itnotonlycanjudgewhetherthepartialdischargehappens,butalsocandeterminethestrengthofdischarge. 4.3.1局部放电测量的基础4.3.1Thebasisofpartialdischargemeasurement 4.3.2局部放电测量的脉冲电流法4.3.2Theimpulsecurrentmethodofpartialdischargemeasurement 4.3.3局部放电测量的非电检测法4.3.3Non-electricmethodofpartialdischargemeasurement本节内容Contentsinthissection(a)示意图(b)等值电路(a)Schematicdiagram(b)Equivalentcircuit4.3.1局部放电测量的基础4.3.1Thebasisofpartialdischargemeasurement图4-12绝缘内部气隙局部放电的等值电路Figure4-12EquivalentcircuitofPDininsulationinternalair-gap设在固体或液体介质内部g处存在一个气隙或气泡，Cg代该气隙的电容，Cb代表与该气隙串联的那部分介质的电容，Ca则代表其余完好部分的介质电容。Assuminganairgaporabubbleexistinginsomewhereinternalofsolidorliquiddielectric,Cgisthecapacitanceofthisairgap,Cbrepresentsthecapacitanceofdielectricwhichisinserieswithairgap,andCaisthecapacitanceofotherintactdielectric.整个系统的总电容为Totalcapacitanceofthewholesystem:在电源电压的作用下，上分到的电压为：Undertheeffectofvoltagesourceu=Umsinwt,Cgundertakesthevoltage:(4-11)(4-12)图4-13局部放电时电压电流变化曲线Figure4-13U-tandI-tcurvewhenPDhappens图4-14一次局部放电的电流脉冲Figure4-14CurrentimpulseduringPD电容上分到的电压thevoltageallocateoncapacitorug气隙放电电压air-gapdischargevoltageUr熄灭电压（剩余电压）extinctionvoltageUs表征局部放电的三个基本Threebasicparametersofpartialdischarge 视在放电量q Apparentdischargemagnitudeq 其中Ca为试品电容，△Ua为气隙放电时，试品两端的压降。q既是发生局部放电时试品Ca所放掉的电荷，也是电容Cb上的电荷增量（比真实放电量小得多）。Intheequation,Caistestsamplecapacitance,△Uaisthevoltagedroponthepolesofsampleunderair-gapdischarge.qrepresentstheelectricchargesthatCareleasedwhenPDhappens,whichisequaltotheincreasedchargesinCb(smallerthanthereleasedchargesinpractical)放电重复率（N）Thedischargerepetitionrate(N)在选定的时间间隔内测得的每秒发生放电脉冲的平均次数。Inaselectedtimeinterval,averagefrequenceofdischargepulsemeasuredinonesecond.放电能量（W）Thedischargeenergy（W）指一次局部放电所消耗的能量Theenergyconsumedinonedischarge其中q为视在放电量，Ui为局部放电起始电压。Whereqisapparentdischargecapacity,Uiisinitialvoltageofpartialdischarge.其他参数Otherparameters平均放电电流Averagedischargecurrent放电的均方率Dischargingmeansquarerate 放电功率Dischargingpower局部放电起始电压Initialvoltageofdischarge局部放电熄灭电压Extinguishingvoltageofdischarge4.3.2局部放电测量的脉冲电流法4.3.2Theimpulsecurrentmethodofpartialdischargemeasurement当发生局部放电时，试品两端会出现一个几乎是瞬时的电压变化，在检测回路中引起一高频脉冲电流，将它变换成电压脉冲后就可以用示波器等测量其波形或幅值，由于其大小与视在放电量成正比，通过校准就能得出视在放电量(一般单位用pC)。此法灵敏度高、应用广泛。Whenpartialdischargehappened,aninstantaneousvoltagechangewillappearinthetwoendsofthetestsample,whichleadsahighfrequencyimpulsecurrentindetectioncircuit,afterconvertingitintovoltagepulsethewaveformandamplitudecanbemeasuredthroughoscillograph.Sinceapparentdischargecapacityisproportionaltothevalue,itcanbeobtainedthroughcalibratingreferencetothevoltagevalue.Characterizedofhighsensitivityanduniversality.4.3.3局部放电测量的非电检测法4.3.3Non-electricmethodofpartialdischargemeasurement噪声检测法Noisetestmethod光检测法Opticaltestmethod化学分析法Chemicalanalysismethod1.噪声检测法Noisetestmethod当绝缘介质中发生局部放电时，其瞬时释放的能量将放电源周围的介质加热使其蒸发，效果就像一个小爆炸。此时放电源如同一个声源，向外发出声波。由于放电持续时间很短，所发射的声波频谱很宽，可达数MHz。Whenpartialdischargehappened,theenergyemittedinstantaneouslycanmakethedielectricaroundthedischargesourceheatedandevaporated,justlikeasmallexplosion.Here,dischargesourceequalstoasoundsourcethatwillgeneratesoundwaves.Asthedischargedurationisveryshort,thesoundwavesspectrumisverywide,uptoafewMHz.介绍一种声测法传感器Introduceanacousticsensor固体中常用传感器为测震仪（Accelerometer）和声发射（AcousticEmission）传感器。Forsolidmedium,accelerometerandacousticemissionsensorarewidelyusedtodetectdischarge.SenacoAS100声传感器北京亚捷隆测控技术有限公司测震仪有着平滑的频率特性，测试频率可达50kHz以上，声发射传感器有多个频段（30k~1MHz），该传感器有很强的方向性，一般来说只能测试某个特定方向的声信号。Accelerometerhassmoothfrequencycharacter,testingfrequencecanreachupto50kHzormore.Acousticemissionsensorhasseveralfrequencychannels(30k~1MHz)featuredingooddirectivity,generallyonlyusedtotestthesoundthatcomesfromspecialdirection.2.光检测法Opticalmethod沿面放电和电晕放电常用光检测法进行测量，而且效果很好。Surfacedischargeandcoronadischargearealwaysmeasuredbyopticalmethod.Andtheeffectisgood.绝缘介质内部发生局部放电时当然会释放光子而产生光辐射放电所发出的光量。不过只有在透明介质的情况下，才能实现。有时可用光电倍增器或影像亮化器等辅助仪器来增加检测灵敏度。WhenPDhappens,photonsgeneratedintheprocesswillcauseopticaldischargeandemitweaklight,whichcanonlybeseenthroughtransparentmedium.Sometimes,withthehelpofsupplementaryinstrumentslikephotoaugetronorimageintensifier,thedetectingsensitivitycanbehigher.3.化学分析法Chemicalanalyticmethod用气相色谱仪对绝缘油中溶解的气体进行气相色谱分析，是20世纪70年代发展起来的试验方法。Theexperimentalmethodofusinggaschromatographicequipmenttoanalyzethedissolvedgasininsulationoilhasbeendevelopedsince1970s. 优点Advantage能够发现充油气体设备中一些用其他试验方法不易发现的局部性缺陷（包括局部放电）。Itcanfindoutsomepartialfaults(includingpartialdischarge)inoil-filledgasequipmentmoreeasilythanusingothermethods.局部放电的检测已成为确定产品质量和进行绝缘预防性试验的重要项目之一。Particaldischargedetectionhasbeenoneofthemostimportantprojectsthatdeterminethequalityandcarryoutpreventiveinsulationexperiment试验内容包括测量视在放电量、放电重复率、局部放电起始电压和熄灭电压、放电的具体部位。Testingcontentsincludemeasuringapparentdischargecapacity,dischargerepetitionrate,particaldischargestartingvoltageandextinctionvoltage,aswellasdischargeposition.小结Summary 表征局部放电的参数主要有：视在放电量、放电重复率、放电能量等。Parametersthatcharacterizepartialdischargeare:apparentdischargecapacity,dischargerepetitionrate,dischargeenergyandsoon. 伴随局部放电会出现多种现象：包括电、光、噪声、气压变化、化学变化等。Severalphenomenaaccompaniedwithpartialdischargeinclude:electric,optical,noise,barometricandchemicalchanges,etc.