1、1,Review of Lecture 7,1. Partial Discharge in Power Capacitors,2. Parameters and Standard,3. Electrical Detection of PD in Capacitor,Contents:,Parameters to estimate the PD of capacitor,Apparent charge, q,Inception voltage, Ui,Extinction voltage, Ue,Change of q with voltage applying time,2,Power Sou
2、rce,Compensation reactor is used in series or parallel with Cx so that to decrease the capacity of testing transformer,Review of Lecture 7,Currents through L and C while the two elements connected in parallel,Voltages across L and C while the two elements connected in series,3,Review of Lecture 7,De
3、tection circuits,Straight detection circuits,Balanced detection circuit,4,Review of Lecture 7,Some problems need to be noticed,Detection impedances is required to withstand large current.,Several detection impedances are needed to match the capacitor samples,Connection types of capacitor elements in
4、fluence detection results.,5,Lecture 8 PD Detection in Power Transformers,电力变压器的局部放电及测量,6,Contents,1. Significance of PD detection in Transformer,电力变压器测量局放的重要性,2. PD Propagation in Windings,4. Detection Circuits for Transformers,5. Calibration,6. The Influence of Discharges in Bushing,3. Test Proced
5、ure and Permissible Apparent Charge,7. Electrical Location of PD in Transformers,局部放电在绕组中的传播,测试程序和允许放电水平,变压器局部放电的测试回路,校正,套管放电的影响,变压器局部放电的电气定位方法,7,1. Significance of PD Detection in Transformer,power frequency withstand test,impulse withstand test,PD often affects the transformers properties in a lon
6、g-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 test is much lower, and the testing
7、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,8,2. PD Propagation in Windings,Equivalent circuit of a transformer winding,C-ground capacitance per unit length,L-inductance per unit length, parasitic inductance,K-series capacitance per unit length, longitudinal capacitance,O-neutral point,A-h
8、igh 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,9,Equivalent circuit of a winding with a cavity discharge source,2. PD Propagation in Windings,10,2. PD Propagation in Windings,Voltage response along the winding,沿绕组的电压响应,11,3. Test Procedure and Permissible Apparent Charge,U1:pre-applied Vol
9、tage 预加电压,U2:measuring voltage 测量电压,Um :the maximum line voltage,During 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,The 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在放电量的50%,Wh
10、en 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,12,3. Test Procedure and Permissible Apparent Charge,During the first step under the test voltage U2, the maximum apparent charge is recorded.,During the seco
11、nd step under the test voltage U2, discharge impulses need to be observed continuously and the maximum apparent charge is recorded.,在电压U2的第一阶段应读数并记录,No record is required under test voltage U1.,在U1阶段无需观测记录,在电压U2第二阶段整个时间内，应连续地观测和记录局部放电水平,13,If the following results are obtained, the PD experiment can
12、 be passed.,3. Test Procedure and Permissible Apparent Charge,During the test procedure, the test voltage never suddenly decreases.,During the last 30 minutes, the magnitudes of all observed impulses are smaller than the permissible apparent charge and do not increase towards the permissible apparen
13、t 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,14,4. Detection Circuits for Transformers,Two ways of the test：induced voltage test and applied voltage test.,Principles 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
14、主纵绝缘都能同时得到所应施加的电压,To execute the test with required voltage on both main insulation and longitudinal insulation.,To use high voltage leads as short as possible.,15,4.1 Detection circuits for single-phase transformers,4. Detection Circuits for Transformers,(a),(b),(c),(d),单相变压器的测试回路,applied voltage,i
15、nduced voltage,16,4.2 Detection Circuits for Three-Phase Transformers,4. Detection Circuits for Transformers,UA=0.25U, UB=0.75U, UC=U,UBC=1.75U,UAC=1.25U,UA=0.5U, UB=U, UC=0.5U,UAB=1.5U,UBC=1.5U,三相变压器的测试回路,17,4. Detection Circuits for Transformers,UA=0.5U, UB=0.5U, UC=U,UAC=1.5U,UBC=1.5U,UA=0.5U, UB
16、=0.5U, UC=U,UAC=1.5U,UBC=1.5U,18,5. Calibration,Co0.1Cx,Cx: entrance capacitance 入口电容,Co：50100pF,Calibration impulse injected from the HV terminal,Calibration impulse injected from the measuring terminal,高压端校正,入口校正,Ck: capacitance of bushing 套管电容,19,5. Calibration,Execute calibration at the place cl
17、ose to the detection terminal.,Requirements of calibration:,Put calibration unit as close as possible to the HV terminal in order to avoid influences of parasitic capacitances.,Record 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,20,6.The Influence of Discharges in Bushing,e.g. Cx=2500pF,Ck=250pF,Qk=20pC, Qx=200pC,21,多端测量定位法,7. Electrical Location of PD in Transformers,Location by multiple-terminal test,Calibration 校正,PD measurement 局放测量,22,The end,
