A New Distance Protection Scheme Based on Improved Virtual Measured Voltage

Fault resistance causes conventional distance protection to operate incorrectly, threatening the safe operation of power system. The immunity to fault resistance is improved by utilizing fault-point voltage, measured current, and setting impedance to construct the virtual measured voltage. Then, a new distance protection scheme, known as protection scheme I, is presented to identify in-zone and out-of-zone faults by comparing the amplitudes of the original and virtual measured voltages. Then, the original and virtual measured voltages are improved by a special voltage phasor in phase with the fault-point voltage phasor. Based on the improved original and virtual measured voltages, another distance protection scheme is presented, namely protection scheme II. The two proposed protection schemes are immune to fault resistance and load current and operate well under all types of faults. However, protection scheme II has higher sensitivity to fault detection compared with protection scheme I. Simulation results verify the correctness and effectiveness of the two proposed schemes.