An improved DC line fault detection scheme using zone partition for MTDC wind power integration systems

The MMC based DC grids are an effective solution to integrate bulk wind power. Under DC faults, the wind power is continuously fed into DC grids, resulting in large fault currents. To guarantee the uninterrupted and safe operation of healthy parts, DC faults should be detected and isolated selectively. Most existing DC fault detection schemes rely on large current-limiting reactors (CLR) to guarantee high selectivity. The reliability of them will be deteriorated under weak boundary conditions. Besides, some schemes fail to identify close-in faults. Though fault detection schemes independent of CLRs are proposed, they cannot work well for remote faults. Hence, to protect the entire transmission line with smaller CLRs, an improved DC fault detection scheme using zone partition is proposed. Firstly, according to different fault distances, internal faults are partitioned into four zones along the transmission line. The fault characteristics in different zones are analyzed. Then, the polarities and arrival times of traveling-waves are used to design the criteria dedicated to different zones. The proposed method is endurable to fault resistance and noise disturbance. Simulation results show that the MTDC wind power integration systems can operate safely during DC fault isolation.