Abstract: A 220kV circuit breaker trip occurred in a 220kV substation of a wind farm, which was caused by abnormal insulation of the DC system. The circuit breaker did not re-close after tripping. This accident analyzed the fault characteristics of tripping caused by the DC system. In this paper, the author gives some suggestions on how to prevent and alleviate the impact of such faults in the future by giving full play to the subjective initiative of operation personnel and processing personnel and improving the integration level of equipment operation and maintenance。