A novel directional relay for AC lines close to the HVDC installation

Compared with traditional distance protection based on fundamental components, the R-L differential-equation algorithm in time domain, which is free of eliminating aperiodic component and insensitive to grid frequency, is more suitable for the AC lines close to high voltage direct current (HVDC) installation. However, there is a problem of voltage dead zone which occurs when the R-L differential equation algorithm is directly applied on the AC lines. According to the difference between fault currents' characteristics provided by direct current (DC) system and receiving-end AC system, then forward and reverse faults on the outlets of AC lines can be identified based on the correlation of the measured voltage drop and calculated voltage drop. Therefore, a novel directional relay based on the correlation coefficient of voltage waveform (CCVW) and low voltage component is proposed. Finally, an extensive performance evaluation in PSCAD/EMTDC and MATLAB simulation verifies the effectiveness of the directional relay. Influencing factors and comparative analysis show that the directional relay has a high sensitivity, rapidity, and reliability.