High reliability overcurrent protection of DC circuit breaker under DC short-circuit fault

When the fault current exceeds the breaking capacity of the DC circuit breaker (DCCB), the overcurrent protection (OCP) needs to be activated to prevent more serious damage to the DCCB. However, at the initial stage of DC short-circuit fault, DCCB will be affected by high-frequency electromagnetic oscillation, which will lead to OCP misjudgment in serious cases. Therefore, a high reliability OCP design method was studied in this paper. Firstly, this paper pointed out that the duration Δt of the DCCB port interference voltage exceeded the OCP threshold voltage during the DC fault, which was the main cause of OCP misjudgment. And the strategy of adding delay time ΔtD at the initial stage of OCP detection was proposed. Secondly, the corresponding relationship between ΔtD and DCCB parallel resonant frequency was proposed, and the lower limit selection method of ΔtD through the impedance measurement of DCCB port was obtained. Finally, the validity of the theoretical analysis was verified in 10kV/15kA DCCB, the error is less than 8%, and the upper limit selection method of Δο was discussed. Taking 200kV DCCB in the project as an example, the theoretical analysis of the range of ΔtD was 1.5μs-60μs.