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1、Review of Lecture 71. Partial Discharge in Power Capacitors2. Parameters and Standard3. Electrical Detection of PD in CapacitorContents: Parameters to estimate the PD of capacitor lApparent charge, qlInception voltage, UilExtinction voltage, UelChange of q with voltage applying time1Power SourceComp
2、ensation reactor is used in series or parallel with Cx so that to decrease the capacity of testing transformerReview of Lecture 7Currents through L and C while the two elements connected in parallelVoltages across L and C while the two elements connected in series2Review of Lecture 7Detection circui
3、ts Straight detection circuitsBalanced detection circuit3Review of Lecture 7Some problems need to be noticeduDetection impedances is required to withstand large current.uSeveral detection impedances are needed to match the capacitor samplesuConnection types of capacitor elements influence detection
4、results.4Lecture 8 PD Detection in Power Transformers电力变压器的局部放电及测量5ContentsContents1. Significance of PD detection in Transformer电力变压器测量局放的重要性电力变压器测量局放的重要性2. PD Propagation in Windings4. Detection Circuits for Transformers5. Calibration6. The Influence of Discharges in Bushing3. Test Procedure and P
5、ermissible Apparent Charge7. Electrical Location of PD in Transformers局部放电在绕组中的传播局部放电在绕组中的传播测试程序和允许放电水平测试程序和允许放电水平变压器局部放电的测试回路变压器局部放电的测试回路校正校正套管放电的影响套管放电的影响变压器局部放电的电气定位方法变压器局部放电的电气定位方法61. Significance of PD Detection in Transformerpower frequency withstand test impulse withstand test PD often affect
6、s the transformers properties in a long-term period. The withstand strength in a short time does not change significantly. Withstand test is destructive, the voltage is so high that insulation is easy to be damaged.工频耐压试验冲击耐压试验局部放电通常影响变压器的长期运行性能，而对短时的耐压强度影响不大。耐压试验是有损试验，容易对绝缘造成破坏The voltage of PD tes
7、t is much lower, and the testing duration is longer (0.51h).局部放电试验的试验电压相对较低，试验持续时间也较长72. PD Propagation in WindingsEquivalent circuit of a transformer windingC-ground capacitance per unit lengthL-inductance per unit length, parasitic inductance K-series capacitance per unit length, longitudinal capa
8、citance O-neutral point A-high voltage end单位长度对地电容单位长度的串联电容 单位长度的电感，即寄生电感 中性点高压端8Equivalent circuit of a winding with a cavity discharge source2. PD Propagation in Windings92. PD Propagation in WindingsnVoltage response along the winding 沿绕组的电压响应103. Test Procedure and Permissible Apparent ChargeU1:
9、pre-applied Voltage 预加电压U2:measuring voltage 测量电压Um :the maximum line voltageoDuring observation, some impulses occasionally occurring with high magnitude can be neglected.在整个试验时间内连续观测，个别较高的脉冲可以忽略oThe noise level is required to be less than 50% magnitude of the highest detected impulse.外围噪声水平应低于规定的视
10、在放电量的50%pWhen test voltage is raised to U2 and decreased from U2, the inception and extinction voltages are recorded.在电压升至U2及由U2降低的过程中，记录起始可能的放电电压和熄灭电压113. Test Procedure and Permissible Apparent ChargepDuring the first step under the test voltage U2, the maximum apparent charge is recorded.pDuring
11、the second step under the test voltage U2, discharge impulses need to be observed continuously and the maximum apparent charge is recorded.U1:pre-applied Voltage 预加电压U2:measuring voltage 测量电压Um :the maximum line voltage在电压U2的第一阶段应读数并记录pNo record is required under test voltage U1.在U1阶段无需观测记录在电压U2第二阶段
12、整个时间内，应连续地观测和记录局部放电水平12 If the following results are obtained, the PD experiment can be passed.3. Test Procedure and Permissible Apparent ChargepDuring the test procedure, the test voltage never suddenly decreases.pDuring the last 30 minutes, the magnitudes of all observed impulses are smaller than
13、the permissible apparent charge and do not increase towards the permissible apparent charge.如果满足两个条件，则试验合格试验过程中，试验电压不产生突然下降在施加电压U2的第二阶段的30分钟内，所有测量的视在放电量连续维持在低于规定的限值，并且不表现出明显地、不断地倾向允许最大限制值增长的趋势134. Detection Circuits for TransformersTwo ways of the test：induced voltage test and applied voltage test.P
14、rinciples of PD circuit selection 两种试验方法：感应加压方式，直接加压方式 试验回路选择采用尽量短的引线在试验中对主纵绝缘都能同时得到所应施加的电压uTo execute the test with required voltage on both main insulation and longitudinal insulation.uTo use high voltage leads as short as possible.144.1 Detection circuits for single-phase transformers4. Detection
15、 Circuits for Transformers(a)(b)(c)(d)单相变压器的测试回路applied voltageinduced voltage154.2 Detection Circuits for Three-Phase Transformers4. Detection Circuits for TransformersUA=0.25U, UB=0.75U, UC=UUBC=1.75U,UACUA=0.5U, UB=U, UCUAB=1.5U,UBC三相变压器的测试回路164. Detection Circuits for TransformersUA=0.5U, UB=0.5
16、U, UC=UUAC=1.5U,UBCUA=0.5U, UB=0.5U, UC=UUAC=1.5U,UBC175. CalibrationCx: entrance capacitance 入口电容Co：50100pFCalibration impulse injected from the HV terminalCalibration impulse injected from the measuring terminal高压端校正入口校正Ck: capacitance of bushing 套管电容185. CalibrationlExecute calibration at the pla
17、ce close to the detection terminal.Requirements of calibration:lPut calibration unit as close as possible to the HV terminal in order to avoid influences of parasitic capacitances.lRecord the detected apparent charges and the relevant detection and calibration places.在测量部位和校正部位要接近为了避免接线杂散电容的影响，标定单元尽量靠近高压端应记录测量部位和校正部位校正要求196.The Influence of Discharges in Bushinge.g. Cx=2500pF,Ck=250pF Qk=20pC, Qx=200pC20多端测量定位法7. Electrical Location of PD in TransformersLocation by multiple-terminal test Calibration 校正PD measurement 局放测量21The end22
