A Novel Line Protection Scheme for a Single Phase-to-Ground Fault Based on Voltage Phase Comparison

Concerning the maloperation or operation-rejection problem caused by the fault resistance, a novel line protection scheme for a single-phase-to-ground fault based on voltage phase comparison is proposed. First, according to phase relationship between the negative-sequence current at the relaying point and the negative-sequence current at the fault point, the angular difference between the measured current and the fault voltage is calculated. Subsequently, with the measured voltage as reference, the phase angles of the voltage at the fault point and the compensatory voltage are calculated. Finally, line protection criterion is formed according to the phase difference between the voltage at the fault point and the compensatory voltage in in-zone and out-of-zone faults. Simulation tests on the real time digital simulator verify that the proposed scheme could identify in-zone and out-of-zone faults correctly, unaffected by the fault resistance, source impedance, and system operating condition. Besides, the operation time and setting value error of the proposed protection scheme both meet the technical requirements of line protection. Furthermore, it is valuable in engineering practice due to the small computation amount.