A novel directional relay for HVDC transmission line based on measured surge impedance

A directional relay based on measured surge impedance is proposed in this paper. When a fault occurs at the forward direction of convertor station, the measured surge impedance at the measuring point is the same as the impedance at rectifier backside. For faults at the backward direction of convertor station, the measured surge impedance at the measuring point is line surge impedance. Thus, according to the difference between the measured surge impedances, fault criterion is proposed to distinguish the forward faults from the backward faults. Moreover, measured surge impedances is calculated by the initial voltage traveling wave and the initial current traveling wave under specific frequencies which are extracted via S transform at the measuring point. Finally, a simulation model of a ±500kV HVDC transmission system is built based on PSCAD/EMTDC, and simulation results of different fault location and transition resistance indicate that this kind of directional relay is validity and adaptability under various fault conditions.