A Reclosing Scheme of Hybrid DC Circuit Breaker for MMC-HVdc Systems

With the increasing demand for large capacity power transmission over long distance, the use of overhead lines is required, which greatly increases the probability of temporary faults. After the faulty line is isolated by hybrid dc circuit breakers (HCBs), the power supply can be restored immediately by reclosing them in the event of temporary fault. However, fragile semiconductor switches will undergo two consecutive faults after the reclose of HCBs when permanent fault occurs. Therefore, a reclosing scheme is proposed in this article to avoid the nonselective reclose of HCBs, whose core principle is an identification method of the instantaneous and the permanent faults. By controlling semiconductor switches in HCB, traveling wave signal is injected into the dc line. Then, whether the fault exists on the line can be determined by the difference in propagation characteristics of the injected signal. The effectiveness of the proposed reclosing scheme is verified by both point-to-point and four-terminal high-voltage dc (HVdc) test systems based on modular multilevel converter built in PSCAD/EMTDC platform. Extensive simulations show that it is robust to fault resistance, etc., and has no identification dead zone. Besides, it has little impact on the healthy part of the system even the permanent fault occurs.