In order to solve to the explosive accident of 500 kV AC filter circuit breaker

different methods such as on-site inspection

disintegration in the factory

detection of the key components

overvoltage simulation

sampling inspection are made on the fault circuit breaker in this paper. Insulation experiments of circuit breaker are carried out on the near phase with AC and DC withstand voltage tests at a high altitude. The near phase is same to the falut circuit breaker in the converter station. The results show that the explosion reasons of the circuit breaker arc-extinguishing chamber are the low insulation margin of the circuit breaker and the poor material of the arcing contact. The metal dust and the metal impurities lead to the distortion of the electric field distribution in the circuit breaker arc-extinguishing chamber. The metal dust is produced during the operation of circuit breaker and the metal impurities come from the assembly process of circuit breaker. Finally

the internal insulation breakdown has been occurred in the circuit breaker arc-extinguishing chamber. According to the special operation conditions for the 500 kV AC filter circuit breaker and the explosion reasons of the arc-extinguishing chamber

some protecting measures are put forward.