局部放电检测原理

1、1Review of Lecture 51. Mechanisms of Dielectric Aging by PD2. Process of Dielectric Aging by PD3. The Influence Factors on Aging Rate4. PD Evaluation ApproachesContents: Electrical aging is a type of dielectric deterioration under the long-term electrical field and due to the fact of partial dischar

2、ges.Definition of Electrical Aging :2Review of Lecture 5Damage of internal discharge to polymer and oil-paperbranched type brush type tree 3Review of Lecture 5The Influence Factors on Aging Rate d c b a HV e 4Review of Lecture 5Estimation by the basic parameters(1) Apparent charge, qa(2) Discharge e

3、nergy and power, W and P(3) The phase angle of pulses (4) Ui and Ue Estimation by the distribution (statistical) graphstqa(t)qitiui00.0020.0040.0060.0080.0100.0120.0140.0160.0180.020-0.500.55Lecture 6 Principles of Electrical Discharge Detection局部放电检测的基本原理61. The Basic Diagram of ERA2. The Detection

4、 Impedance3. The Amplification of Impulses4. Detection Sensitivity5. Impulse Resolution6. Calibration7CxZdZmeCkoA1. The Basic Diagram of ERA1. A high-voltage source e, free of discharge.2. A sample cx affected by discharges.3. An impedance Zd4. A coupling capacitance Ck6. An amplifier A7. An observa

5、tion unit O高压电源，无局放试品检测阻抗耦合电容放大器观测单元ui5. A protecting impedance Zm保护阻抗，低通滤波81. The Basic Diagram of ERACxZdZmeCkoACxZdZmeCkoATwo connecting methods (the location of Zd in circuit):1. In series with the sample Cx- Series circuit.2. In series with the coupling capacitor Ck- Parallel circuit.Series cir

6、cuitParallel circuit串联回路并联回路92. The Detection ImpedanceFunctions:(1) to transfer the impulse current into voltage and(2) to suppress the interferences of power frequency and harmonic from source.CdRdCdRdCdLdRdCdLdRd取得局部放电所产生的高频脉冲信号抑制试验电压的工频及其谐波的低频信号102.1 the RC circuit2. The Detection ImpedanceCdRdC

7、kCxABu/dkdkxCCCCCqudkkdmCCCuudkkdkdkxCCCCCCCCqxkddCCCCq)1 ( )1 (kdxdvCCCCCvdmCquduDischarge extinguishes, Cd discharges via Rdddtdmtdmdeueutu/)(dkxkxddtdRCCCCCRC )(Ct，Tuned capacitance调谐电容tvddeCqtu)()/(1tddCRDamping constant 衰减常数112. The Detection Impedancedmu)(tudt2/122)()(dvdCqUFrequency spectrum

8、of RC circuittvddeCqtu)(If considering the rising edge of impulse )(/11)1 ()(/ttfdvtddfddeeCqeutuFTfUdm2dmU)(),(fUUddh2df,tdhCR1tddCRf2123dB12(1)The height of the impulse is proportional to the magnitude q of the discharges.(2) Cd ud m sensitivity .检测阻抗上的脉冲高度与放电量q成正比一定的q下，减小Cd可以增大udm ,提高灵敏度xkdddmCCC

9、Cqu)1 ( (3)A coupling capacitance Ck is needed, substituting arbitrary capacitance for Ck results in a very small udm 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. The Detection ImpedanceSome conclusions of RC circuit:132. The Detection ImpedancedU)(tudt(4) The height of the impulse is in

10、dependent of Rd. however, R d , the impulse become so sharp and will not be amplified fully in some amplifier, which result in smaller impulse amplitude sensitivity.测量得到脉冲高度虽然与Rd无关，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.)/(1tddCRxkdddmCCCCqu)1 ( (5)The impulses detected by RC circuit is unidirectional an

11、d one-to- one corresponding to discharge, d resolutionRC上的脉冲与放电脉冲一一对应，脉冲持续时间短分辨率越高142. The Detection ImpedancedU)(tudt )(/11)(ttfdvdfdeeCqtudvfdfdvdCqCqdttu11/11)(0(6) The integral of ud(t) with respect to t is independent on f. An integrated circuit is convenience for observation of q . e.g. lower

12、frequency amplifierUd(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q，比如采用低频放大器.15tud(t)2. The Detection Impedance2.2 the RLC circuitCdRdCkCxABLdLRC circuitduu)2/(1tddCRtddCL1The impulse is an attenuated oscillation with the same crest voltage as with an RC circuit. 衰减振荡波，同RC回路峰值相等Damping constantOscillating an

13、gular frequency衰减系数振荡角频率)cos()(teCqtudtvddddcos)cos()/(11)(2tdtfdvdfdeteCqtu ba162. The Detection Impedancetud(t)a b 212222222122/dddddVdLRCqU dUd17)cos()(teCqtudtvdd)1 (kdxdvCCCCC2. The Detection ImpedanceSome conclusions of RLC circuit:(1)The height of the impulse is proportional to the magnitude

14、q of the discharges.脉冲高度仍然与放电量大小成正比(2)The maximum of Ud(w) occurs at =d , and the signal must be amplified by the amplifier that have a bandwidth being equal to, or larger than that of the signal. dUd需选用中心频带范围等于d或者稍宽一些的放大器，可以对信号中大部分能量进行放大(3) The maximum sensitivity can be obtained when Cd0 and CkCd

15、灵敏度最大的条件为Cd0及CkCd 183. The Amplification of ImpulsesfA121fa1fa2fA121f0f(1)wide-band and low-frequency amplifier3.1 Classification of amplifier(2)tuning amplifierfa1(lower limit frequency): k Hz3dBfa2(upper limit frequency): MHz (wide-band), 100300kHz (low-frequency) Narrow band: f is about 10k Hz, f

16、0 is adjustable,Median band: f is about 100k Hz.窄频带中频带宽频带和低频放大调谐放大器19CxZmeCkRaARdCaudAmplifierua3. The Amplification of Impulses(1)After RC CircuitAmplifier : an ideal amplifier and a low pass filter 理想放大器+低通滤波器tvddeCqtu)(22/1aaaafCRadttavadaeeCqAtu)(22)2/(1dtddfCRfA121fa1fa2aaaCRf212fUdm2dmU)(),(fU

17、Uddh2df,3.2 Characteristics of amplifier203. The Amplification of ImpulsesdaadttavadaeeCqAtu)(1)()(ttvaadeeCqAtu1/adttvdaeeCqAtuda(2)()(ttdavadaeeCqAtutdetaeuttaetdeWide-band amplifierlow-frequency amplifierdvdCqdttu0)(Integral amplifier!213. The Amplification of Impulses(2) After RLC CircuitCxZmeCk

18、RaGRdCaLaLdCdAmplifieruduaFrequency selecting amplifier : an ideal amplifier and a tuning circuit调谐放大器uatuat(1) a d: response (2) a d: response response response dUd224. Detection Sensitivity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电荷大小Noise sources:n from the amplifiern from the circuit.噪声来源放大器测试回路4.724.734.74

19、4.754.764.77x 10-3-0.1-0.0500.050.1tUUsUnSNR=Us/Un 234. Detection Sensitivity4.1 Sensitivity by amplifier noise以放大器噪声决定检测灵敏度,)(tvddeCqtu)1 (kdxdvCCCCC)(tudA(f1,f2)vamCqAuZd2namuunvsuCq22NSvnsCuq2vsCq signalvamCqu244. Detection Sensitivity4.2 Sensitivity by circuit noiseThe effective voltage of the n

20、oise over the detection resistor:teffCKTUK-Boltzmanns constantCt-the capacitance between A and BT-the absolute temperatureCdRdCkCxABA BtnCKTU5 . 2The amplitude of noise is about 2.5 times as large as Ueff噪声的幅值是其有效值的约2.5倍，因此噪声的幅值Un为kxCCn/vnCKTnU) 1(5 . 2)/(kxkxtCCCCCdC)1 (kdxdvCCCCCvvsCKTnCq) 1(5 . 2

21、2vsCKTnq) 1(5vsCq 检测阻抗电阻器上的噪声电压有效值254. Detection SensitivityvAsCqvCsCq)1 (kdxdvCCCCCqs determined by amplifier (qAs)noise is larger than that of by circuit noise(qCs)以测试回路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CxZmeCkRdACdBy amplifierBy circuitThe circuit noise is stepped-up by a transformer and added to the am

22、plifier1:N用变压器将回路噪声升高至超过放大器噪声265. Impulse ResolutionThe degree to which the impulses can be separated is given by the resolution, which is defined as the number of impulses that can be distinguished in one quadrant of a 50Hz sine wave. uthe resolution of the detection circuit脉冲分辨率是指在50Hz正弦波的一个象限内，能分

23、辨的脉冲数。Impulse resolution dependents onuthe resolution of the oscilloscope screenuThe resolution of the amplifier检测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275. Impulse Resolution5.1 the resolution of the detection circuit(1) RC circuittvddeCqtu)(vCq)(tudttddCR)/(1tddCRDamping constant 衰减常数Time constant 时间常数In order

24、 to be seen separated, the impulses must recur after a time interval which is 1.5 to 3 times the time constant d of the impulses.为了使各个脉冲能充分分辨，脉冲必须经过约1.53倍的时间常数d ，tddRCRt35 . 135 . 1Rtr/4501d3/4501tdCR6001285. Impulse Resolution(2) RLC circuit)cos()(teCqtudtvdd)2/(1tddCRDamping constant 衰减常数tddCR2Tim

25、e constant 时间常数dRt3tdCR6Rtr/4501tdCR6/4501tdCR12001295. Impulse Resolution5.2 the resolution of the amplifierfA121f0fThe resolution of amplifier depends on its bandwidthf放大器的分辨率取决于它的频带宽度f(1) Tuning amplifierfCRaaa12fftaR133Rtr/4501f1/4501200f(2) wide-band or low frequency amplifier221fCRaaaf21fftaR2

26、1233Rtr/4501f21/4501100ffA121fa1fa2aaaCRf212305.3 the resolution of the oscilloscope screen示波器屏幕分辨率5. Impulse ResolutionThe minimum thickness of the luminous line on a normal oscilloscope screen is about 0.2mm示波器上可分辨的发光线最小宽度约为0.2mmIf the screen has a width of 100mm, it can resolve a maximum of 500 l

27、ines or impulses. Two quadrants of the 50Hz sine wave usually are displayed over the full width of the screen. Consequently, a maximum of 250 impulses per quadrant can be resolved.5002 . 010025021500r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=250315.4 the total resolution5. Impulse Resolutiondetection circuit(1) RC circuitRtr/4501tdCR6001(2) RLC circuitRtr/4501tdCR12001amplifier(1) Tuning amplifier200fRtr/4501(2) wide-band or low frequency amplifierRtr/4501100foscilloscope screen250241500rrto