Abstract: Briefly describe the troubleshooting process of a 10 kV bus voltage abnormal accident in a 110 kV substation. The operation and maintenance personnel first conducted a routine inspection, measurement and analysis of the 10 kV line to identify the cause of the accident. After several twists and turns, it was finally concluded that the accident was caused by the arc suppression coil inside the station. Through the analysis of the accident investigation process, we have come to realize that the analysis of the causes of distribution line faults needs to broaden our thinking; The equipment inside the station and the outgoing lines outside the station should be considered simultaneously; Improve the ability of dispatch and operation personnel to analyze, judge, and solve accidents. Effectively shorten the time for finding the cause of accidents and improve the reliability of distribution network power supply.