Abstract: The circuit breaker of AC filter in converter station is an important part of HVDC system. The

occurrence of internal faults will directly affect the stable operation of HVDC system. In view of the fault diagnosis

of the circuit breaker for filter，an efficient online monitoring method was proposed to diagnose the health status of the circuit breaker according to the on-off current of the AC filter circuit breaker. Firstly，the time-domain and

frequency-domain characteristics of the switching current in the AC filter circuit breaker were analyzed. Then，the

frequency-domain analysis method of the inrush current in the circuit breaker opening and closing based on

segmented random fast Fourier transform（FFT）was used to realize the real-time monitoring and judgment of the

fault information；finally，based on the data of C phase fault recording for the 750 kV AC filter field 7632 circuit

breaker in Lingzhou converter station，the validity analysis and verification of diagnosis strategy were carried out.

Combined with the circuit breaker disassembly and inspection，the effectiveness of the fault diagnosis strategy

proposed was verified. It provides a reliable solution for the on-line diagnosis of circuit breaker fault in AC filter in

converter station，and has good engineering application value.

      Key words: converter station；AC filter；circuit breaker；fault diagnosis；segmented fast Fourier transform

（FFT）