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1、Lecture 7 PD Detection in Power Capacitors电力电容器的局部放电测量1ContentsContents1. Partial Discharge in Power Capacitors电力电容器中的局部放电电力电容器中的局部放电2. Parameters and Standard测试参数及相关规程测试参数及相关规程3. Electrical Detection of PD in Capacitor电力电容器的局部放电电测法电力电容器的局部放电电测法21. Partial Discharge in Power Capacitors1.1 the charac
2、teristics of power capacitorsoInsulation structure of capacitors: oil-impregnated papers, oil-impregnated dielectric membrane and their combination.绝缘结构：油浸纸，浸渍薄膜及其组合oExtremely high electrical field stress exists in capacitors and partial discharges are very possible to occur inside.介质工作场强特别高，内部特别容易发
3、生局部放电电力电容器的特点31.2 Inception and damage of PD in power capacitor 1. Partial Discharge in Power CapacitorsThe lifetime of capacitor suffering from PD decreases exponentially. PD is a key factor that results in expanding and incipient fault of power capacitor. 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
4、早期损坏的一个重要因素 42. Parameters and Specification2.1 Parameters to estimate the PD of capacitor lApparent charge, qlInception voltage, UiThe AC voltage across the capacitor at which the discharge magnitude exceeds a given value qg. 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Inception voltage (stress): The AC voltage
5、 (stress) across the sample at which discharges start to occur when the voltage is increased .5lExtinction voltage, 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。The AC voltage across the capacitor at which the discharge magnitude is less than the given magnitude qg. a is better than b2. Parameters and Specificationl
6、Change of q with voltage applying time放电量随加压时间的变化62.2 Procedure of PD detection2. Parameters and StandardsU1:pre-applied Voltage 预加电压 Type U1 (kV) U2 (kV) U3 (kV) Requirement Note Shunt capacitors 2.15un, 1s 1.2un, 10min 1.5un, 10min Series-connected capacitors 4.5un, 1s 1.6un, 10min Breaker capacit
7、ors 1.8un, 1s 1.1un, 10min During last 10min, no PD impulses with increased magnitude are observed. un is working voltage. U1 U2 U3 t1 t2 t3 U2:holding voltage 保持电压U3:measuring voltage 测量电压7u Power source: sine wave, 50Hz,60HzuThe capacitance difference before and after test should not exceed the di
8、fference caused by a fuse burning out.uA simulating small capacitors can be used when sensitivity or capacity could not meet the test requirements.2. Parameters and Standards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。83. Electrical Detection o
9、f PD in CapacitorThe capacity of a power capacitor is much larger than the usual HV equipments. Large capacity of the power source is required for PD experiment of capacitors. 3.1 Power Source and Circuits(1) Power sourceCompensation reactor is used in series or parallel with Cx so that to decrease
10、the capacity of testing transformerCurrents through L and C while the two elements connected in parallelVoltages across L and C while the two elements connected in series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9(2) Detection circuits e.g.CkqsCv3. Electrical Detection of
11、PD in Capacitorsensitivity10nA Balanced detection circuit is recommended3. Electrical Detection of PD in CapacitoruThe straight detection circuits may be used. In order to obtain high sensitivity, the coupling capacitor should be at least as large as the sample. A second sample is used as the coupli
12、ng capacitor, Ck=Cx.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11(2) The influence of internal inductance3.2 Some problems need to be noticed(1) Requirements of detection impedancesuThe capacitance range of power capacitors is larger than that of many other HV equipments，several detection impedances are needed
13、to match the capacitor samples, so that to get the proper frequency-band and sensitivity.3. Electrical Detection of PD in Capacitor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。uDetection impedances is required to withstand large current.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12(2) Conne
14、ction types of capacitor elements influence detection results.3. Electrical Detection of PD in Capacitor电容器元件的连接形式会影响检测结果。13(3) The influence of internal inductancePower capacitor is not pure capacitance. The internal inductance comes from :internal leads, leading out wires, capacitor elements connecting in series or parallel. H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。LHInfluences on PD detection:nresult in measurement error nCalibration results 3. Electrical Detection of PD in Capacitor内部电感的影响ndecrease the sensitivity, resolution测量结果误差降低灵敏度，分辨率错误的标定结果14The End15
