Objective In recent years, safety operation problems of urban rail transit traction power supply system are attracting widespread attention. On actual operation lines, the frequently occurred rail potential abnormal rise and the frequent actions of OVPD (over-voltage protection device) threaten the safety of personnel and surrounding equipment. It is necessary to carry out in-depth analysis and research into the intrinsic mechanisms of these abnormal phenomena.

Method First, steady-state models for the traction power supply system and the return current system are established respectively, and a segmented calculation method between the models is designed. Second, the influence of transient parameters on rail potential and OVPD is analyzed, a transient model is established, then a joint modeling method of transient-state and steady-state rail potential (hereinafter referred to as "transient-steady-state") is proposed. Finally, the accuracy of the transient-state model is verified based on actual line simulation.

Result & Conclusion  Under normal operating conditions, the steady-state results and transient-state results of the rail potential distribution are basically close, thereby verifying the correctness of the transient-state model. In the steady-state model, the rail potential value cannot be changed within 1 second, making it impossible to observe the dynamic changes of rail potential within 1 second, even the microsecond-level instantaneous changes, nor to calculate the instantaneous transient overvoltage caused by OVPD tripping. However, the transient-state model can effectively solve this problem. Although OVPD action can reduce the rail potential at a certain location, it may cause an increase in rail potential across the entire line and even lead to miss operation of other OVPDs. This is the main reason for the frequent actions of OVPD.