局部放电检测原理

ReviewofLecture51.MechanismsofDielectric

AgingbyPD2.ProcessofDielectric

AgingbyPD3.TheInfluenceFactorsonAgingRate4.PD

EvaluationApproachesContents:Electricalagingisatypeofdielectricdeteriorationunderthelong-termelectricalfieldandduetothefactofpartialdischarges.DefinitionofElectricalAging:精品资料1ReviewofLecture5Damageofinternaldischargetopolymerandoil-paperbranchedtypebrushtypetree精品资料2ReviewofLecture5TheInfluenceFactorsonAgingRateElectricalfieldstressVoltagefrequencySituationofcavityandgascontentsinsideTemperatureandhumidityMechanicalforce精品资料3ReviewofLecture5Estimationbythebasicparameters(1)Apparentcharge,qa(2)Dischargeenergyandpower,WandP(3)Thephaseangleofpulses(4)UiandUeEstimationbythedistribution(statistical)graphs精品资料4Lecture6PrinciplesofElectricalDischargeDetection局部(júbù)放电检测的基本原理精品资料5Contents1.TheBasicDiagramofERA2.TheDetectionImpedance3.TheAmplificationofImpulses4.DetectionSensitivity5.ImpulseResolution6.Calibration脉冲电流法基本原理检测(jiǎncè)阻抗脉冲(màichōng)放大检测灵敏度脉冲分辨率放电量标定精品资料61.TheBasicDiagramofERA1.Ahigh-voltagesourcee,freeofdischarge.2.Asamplecxaffectedbydischarges.3.AnimpedanceZd4.AcouplingcapacitanceCk6.AnamplifierA7.AnobservationunitO高压电源，无局放试品检测(jiǎncè)阻抗耦合电容(diànróng)放大器观测单元Δu5.AprotectingimpedanceZm保护阻抗，低通滤波精品资料71.TheBasicDiagramofERATwoconnectingmethods(thelocationofZdincircuit):1.InserieswiththesampleCx-Seriescircuit.2.InserieswiththecouplingcapacitorCk-Parallelcircuit.SeriescircuitParallelcircuit串联(chuànlián)回路并联(bìnglián)回路精品资料82.TheDetectionImpedanceFunctions:(1)totransfertheimpulsecurrentintovoltageand(2)tosuppresstheinterferencesofpowerfrequencyandharmonicfromsource.RCcircuitRLCcircuit取得局部放电所产生(chǎnshēng)的高频脉冲信号抑制试验电压的工频及其谐波的低频(dīpín)信号精品资料92.1theRCcircuit2.TheDetectionImpedanceDischargeextinguishes,CddischargesviaRdCt，Tunedcapacitance调谐电容Dampingconstant衰减常数精品资料102.TheDetectionImpedanceFrequencyspectrumofRCcircuitIfconsideringtherisingedgeofimpulseFT3dB精品资料11(1)Theheightoftheimpulseisproportionaltothemagnitudeqofthedischarges.(2)Cd↘→Δudm↗→sensitivity

↗.检测阻抗上的脉冲高度(gāodù)与放电量q成正比一定(yīdìng)的q下，减小Cd可以增大Δudm,提高灵敏度(3)AcouplingcapacitanceCkisneeded,substitutingarbitrarycapacitanceforCkresultsinaverysmallΔudm

→sensitivity↘.耦合电容是必须的，采用杂散电容替代Ck导致测量得到的脉冲幅值会变得非常小,降低灵敏度2.TheDetectionImpedanceSomeconclusionsofRCcircuit:精品资料122.TheDetectionImpedance(4)TheheightoftheimpulseisindependentofRd.however,R↘→

αd

↗,theimpulsebecomesosharpandwillnotbeamplifiedfullyinsomeamplifier,whichresultinsmallerimpulseamplitude→sensitivity↘.测量得到脉冲高度虽然与Rd无关(wúguān)，但降低Rd会使得脉冲下降变快，频谱变宽，对放大器要求高，降低灵敏度.(5)TheimpulsesdetectedbyRCcircuitisunidirectionalandone-to-onecorrespondingtodischarge,αd

↗→resolution↗RC上的脉冲(màichōng)与放电脉冲(màichōng)一一对应，脉冲(màichōng)持续时间短分辨率越高精品资料132.TheDetectionImpedance(6)Theintegralofud(t)withrespecttotisindependentonαf.Anintegratedcircuitisconvenienceforobservationofq.

e.g.lowerfrequencyamplifierUd(t)对时间的积分与上升沿无关，与q成正比，因此适合采用积分式电路观测(guāncè)q，比如采用低频放大器.精品资料14tud(t)2.TheDetectionImpedance2.2theRLCcircuitLRCcircuitTheimpulseisanattenuatedoscillationwiththesamecrestvoltageaswithanRCcircuit.衰减振荡波，同RC回路峰值(fēnɡzhí)相等DampingconstantOscillatingangularfrequency衰减系数振荡(zhèndàng)角频率ba精品资料152.TheDetectionImpedanceab精品资料162.TheDetectionImpedanceSomeconclusionsofRLCcircuit:(1)Theheightoftheimpulseisproportionaltothemagnitudeqofthedischarges.脉冲高度(gāodù)仍然与放电量大小成正比(2)ThemaximumofUd(w)occursatω=ωd

,andthesignalmustbeamplifiedbytheamplifierthathaveabandwidthbeingequalto,orlargerthanthatofthesignal.需选用中心频带范围等于ωd或者稍宽一些的放大器，可以对信号(xìnhào)中大部分能量进行放大(3)ThemaximumsensitivitycanbeobtainedwhenCd≈0andCk>>Cd灵敏度最大的条件为Cd≈0及Ck>>Cd

精品资料173.TheAmplificationofImpulses(1)wide-bandandlow-frequencyamplifier3.1Classificationofamplifier(2)tuningamplifierfa1(lowerlimitfrequency):kHz3dBfa2(upperlimitfrequency):MHz(wide-band),100~300kHz(low-frequency)

Narrowband:

Δfisabout10kHz,f0isadjustable,Medianband:

Δfisabout100kHz.窄频带(píndài)中频带(píndài)宽频带和低频放大调谐放大器精品资料183.TheAmplificationofImpulses(1)AfterRCCircuitAmplifier:anidealamplifierandalowpassfilter理想(lǐxiǎng)放大器+低通滤波器3.2Characteristicsofamplifier精品资料193.TheAmplificationofImpulses(1)(2)Wide-bandamplifierlow-frequencyamplifierIntegralamplifier!精品资料203.TheAmplificationofImpulses(2)AfterRLCCircuitFrequencyselectingamplifier:anidealamplifierandatuningcircuit调谐(tiáoxié)放大器(1)α

a>αd:αresponse

(2)α

a<αd:βresponseαresponse

βresponse

精品资料214.DetectionSensitivitySensitivity:Thesmallestpartialdischargethatcanbeobservedforacertainsignal-to-noiseratio(SNR≧2).灵敏度：在保证一定的信噪比条件下，所能检测到的最小视在放电(fàngdiàn)电荷大小Noisesources:fromtheamplifierfromthecircuit.噪声(zàoshēng)来源放大器测试回路SNR=Us/Un≧2精品资料224.DetectionSensitivity4.1Sensitivitybyamplifiernoise以放大器噪声(zàoshēng)决定检测灵敏度signal精品资料234.DetectionSensitivity4.2SensitivitybycircuitnoiseTheeffectivevoltageofthenoiseoverthedetectionresistor:K-Boltzmann’sconstantCt-thecapacitancebetweenAandBT-theabsolutetemperatureABTheamplitudeofnoiseisabout2.5timesaslargeasUeff噪声(zàoshēng)的幅值是其有效值的约2.5倍，因此噪声(zàoshēng)的幅值Un为检测阻抗电阻器上的噪声(zàoshēng)电压有效值精品资料244.DetectionSensitivityqsdeterminedbyamplifier(qAs)noiseislargerthanthatofbycircuitnoise(qCs)以测试回路(huílù)噪声决定的检测灵敏度要比以放大器噪声决定的检测灵敏度高ByamplifierBycircuitThecircuitnoiseisstepped-upbyatransformerandaddedtotheamplifier1:N用变压器将回路噪声(zàoshēng)升高至超过放大器噪声(zàoshēng)精品资料255.ImpulseResolutionThedegreetowhichtheimpulsescanbeseparatedisgivenbytheresolution,whichisdefinedasthenumberofimpulsesthatcanbedistinguishedinonequadrantofa50Hzsinewave.theresolutionofthedetectioncircuit脉冲(màichōng)分辨率是指在50Hz正弦波的一个象限内，能分辨的脉冲(màichōng)数。ImpulseresolutiondependentsontheresolutionoftheoscilloscopescreenTheresolutionoftheamplifier检测(jiǎncè)单元分辨率放大器分辨率示波器分辨率脉冲分辨率取决于精品资料265.ImpulseResolution5.1theresolutionofthedetectioncircuit(1)RCcircuitDampingconstant衰减常数Timeconstant时间常数(shíjiānchánɡshù)Inordertobeseenseparated,theimpulsesmustrecurafteratimeintervalwhichis1.5to3timesthetimeconstantτdoftheimpulses.为了使各个脉冲(màichōng)能充分分辨，脉冲(màichōng)必须经过约1.5~3倍的时间常数τd，精品资料275.ImpulseResolution(2)RLCcircuitDampingconstant衰减常数Timeconstant时间常数(shíjiānchánɡshù)精品资料285.ImpulseResolution5.2theresolutionoftheamplifierTheresolutionofamplifierdependsonitsbandwidthΔf放大器的分辨率取决于它的频带宽度Δf(1)Tuningamplifier(2)wide-bandorlowfrequencyamplifier精品资料295.3theresolutionoftheoscilloscopescreen示波器屏幕(píngmù)分辨率5.ImpulseResolutionTheminimumthicknessoftheluminouslineonanormaloscilloscopescreenisabout0.2mm示波器上可分辨(fēnbiàn)的发光线最小宽度约为0.2mmIfthescreenhasawidthof100mm,itcanresolveamaximumof500linesorimpulses.Twoquadrantsofthe50Hzsinewaveusuallyaredisplayedoverthefullwidthofthescreen.Consequently,amaximumof250impulsesperquadrantcanberesolved.屏幕宽度为100mm,可分辨最多500个脉冲，100mm为2个象限的宽度，因此分辨率为500/2=250精品资料305.4thetotalresolution5.ImpulseResolutiondetectioncircuit(1)RCcircuit(2)RLCcircuitamplifier(1)Tuningamplifier(2)wide-bandorlowfrequencyamplifieroscilloscopescreenrtotalisdeterminedbythesmallestone!总的分辨率由最小的一个(yīɡè)决定精品资料316.Ca