Study of a Combined Surge Protective Device for a Relay Protection Circuit in a UHV Converter Station

This article focuses on the problem that the voltage recovery time of relay protection circuits in converter stations is too long under lightning surges. A surge protective device (SPD) in a relay protection circuit in an ultrahigh-voltage (UHV) converter station is investigated. Based on the action characteristics of a gas discharge tube (GDT) and metal oxide varistor (MOV) under a 1.2/50 μs lightning surge, the equivalent circuit model of a series-combined SPD is established. In the equivalent circuit model, this study considers the breakdown voltage, nonlinear impedance, parasitic capacitance, stray inductance and other parameters of GDTs and MOVs. Simulation analysis shows that a series-combined SPD can significantly increase the residual voltage and shorten the voltage recovery time of the protected system. To verify the simulation results, a test platform based on a low-voltage DC voltage divider was built for the lightning surge test. The test results are consistent with the simulation results, verifying that a series-combined SPD can meet the dual surge protection requirements of peak suppression and fast voltage recovery.