Fault property identification method and application for MTDC grids with hybrid DC circuit breaker

In order to ensure that the healthy lines continue to operate after the line fault, the multi-terminal high voltage direct current (MTDC) grid based on half-bridge modular multilevel converter (HB-MMC) prefers to isolate the fault line using DC circuit breakers (DCCBs). Since most of overhead (OH) line faults are instantaneous faults, after the fault line is isolated, usually the DCCB will reclose with a certain delay to improve system stability. For fear of reclosing to permanent fault, this paper proposes a fault property identification (FPI) method suitable for MTDC grids with hybrid DCCBs (HDCCBs), which can distinguish between instantaneous and permanent faults. The method is based on the characteristic signal injected by the HDCCB with the auxiliary circuit. Besides, once a permanent fault has been determined, the method can also locate the fault position accurately. The effectiveness of the proposed FPI method is verified by extensive simulations in PSCAD/EMTDC platform.