The abnormal fault of high secondary voltage of 500 k V capacitor voltage transformer is introduced in this paper. It is judged preliminarily on the basis of the structural characteristics

electrical principles

capacitance and dielectric loss test of the capacitor voltage transformer that the fault is due to breakdown of 6～8 pieces of high-voltage capacitor elements of the capacitor voltage transformer. It is found throughout disassembly

inspection and analysis of the equipment that 7 pieces of high-voltage capacitor elements are breakdown and the surface of the aluminum foil has indentation and wrinkle. It is inferred that there are process issues during manufacturing process. The correctness of the theoretical calculation is verified and the fault of the equipment is found out. The mapping of the number of capacitor element breakdowns and the variation rate of secondary output voltage is derived and a warning value is set. The preventive sugegstions for the equipment supplier and operation as well as maintenance side are posposed with combination of operation experience so to assure safe and stable operation of the equipment.