Simulation and analysis of HVDC line protection under the single pole to ground fault with high transition resistance

In the process of the single pole to ground fault occurred on the high voltage direct current (HVDC) transmission line, the sensitivity of the HVDC line main protection will reduce with the increasing of the transition resistance. Once the value of the transition resistance is bigger than a certain value, the HVDC line main protection operates inaccuracy which results in the blocking of the fault pole line without the fault recovery and restart course. For a transient fault, this mal operation will cause the transmission line out of operation unnecessarily. Since the transmission capacity of the HVDC line is large, a short time out of operation accident will cause big pressure to the power supplier. In order to avoid this problem, this paper analyzes the reason of the mal operation under the high transition resistance fault and proposes an improved solution in the end of the paper. Typical ±500kV HVDC transmission system in Chinese power system is constructed by EMTDC for the simulation. The simulation results prove the accuracy of the proposed method.