Frequent input and elimination for AC filter will superpose the circuit breaker a large DC residual voltage

and the influences of environmental factors easily lead to circuit breaker flashover faults

which will cause a serious threat to the safe and stable operation of HVDC system. We analyzed a 500 kV converter AC filter circuit breaker flashover accident by combining with the wave recording and field test. It is found that harsh weather conditions and the superposition between DC voltage on power side and the voltage on AC side will cause the circuit breaker interrupter insulating flashover and interphase flashover. For solving the reducing of AC filter circuit breaker insulation

we experimentally analyzed the circuit breaker external insulation flashover characteristic and improvements in the external insulation pollution flashover voltage. It is found that the pollution flashover voltage will significantly reduce with the salt density and ash dense increasing

and the installation of the creeping increasing skirt or spraying PRTV coating can significantly enhance the pollution flashover voltage. According to the test results

the corresponding measures to prevent the circuit breaker pollution flashover are put forward

and the good application results are obtained.