某500kV CVT的故障原因诊断及分析

Diagnosis and Analysis of a Fault of 500 kV Capacitor Voltage Transformer

针对一起由500 kV电容式电压互感器(CVT)的A相二次电压异常不稳定升高引起保护动作的故障,通过对该CVT的A相进行诊断试验发现,其上节耦合电容器的介损、绝缘电阻及电容值均严重不合格,初步分析是上节耦合电容器密封盖密封不严导致受潮,形成内部部分绝缘贯穿性放电通道,使得部分电容器元件被击穿或短接。通过吊芯检查证实了上部密封盖密封不严导致此CVT在一年的运行中逐渐受潮,电容器心子上有部分电容器元件被击穿或短接的放电痕迹。分析指出,部分电容器元件的被击穿或短接造成了分压比的变化,从而导致二次电压的升高,引起保护动作。

As for the secondary protection action caused by instable rise of secondary voltage of phase A of 500 kV capacitor voltage transformer（ CVT）, it is found through diagnosis and test of phase A of CVT that the dielectric loss factor, the dielectric resistance and capacitance of the upper coupling capacitor segment are severely unqualified. It is pointed in the preliminary analysis that the failure of seal cover gradually leads to inner damp, causing break-down or short-circuit of some inner capacitance sections. According to disassembly inspection, it is proved that un-tight sealing cover leads to moisture in such batch of CVT in 1 year＇ s continuous operation and the trace of breakdown or short- circuit of some capacitance sections exists. It is pointed out in the analysis that the breakdown or short-circuit of some capacitance sections causes the change of voltage ratio, which rises the secondart voltage and leads to the protection action.