Fault detection and protection in a meshed MMC-HVDC grid based on bus-voltage change rate and fault component current

Fault protection for a modular multi-level converter (MMC)-based high voltage direct current (HVDC) grid with dc circuit breakers (DCCBs) is a great challenge, because faults need to be isolated fast to prevent the collapse of the grid and overcurrent damage to the equipment. Before clearing faults, faults must be detected as soon as possible. However, the fast rising speed of fault currents and the emerging fault between the DCCB and line reactor increase the difficulty of fault protection. A fast and reliable fault detection and protection method relying on bus-voltage change rate and fault component current is proposed in this paper. It requires the measurements with local sensors and makes use of a lower number of voltage sensors. The proposed algorithm is applied to a four-terminal MMC-HVDC grid. Results show that the proposed method can identify the fault type and discriminate bus faults, line faults, and wall bushing faults. It can detect faults quickly and does not generate erroneous and unnecessary trip signals.