Selectivity Enhancement Scheme for Zero-sequence Current Protection Based on Distance Relay for High-resistance Grounding Fault

The last section of zero-sequence current protection of AC line adopts 300 A, which has the risk of disordered tripping. Therefore, a new principle of high-resistance grounding distance relay based on zero-sequence reactance line and non-fault phase polarization is proposed. The relay adopts the technical route of phase selection before measurement. The phase selection element combines zero-sequence reactance line and non-fault phase polarization method to form a variety of combined criteria to complete the phase selection. Due to the phase difference between the zero-sequence current at the protection installation site and the zero-sequence current at the fault point, the zero-sequence reactance lines of the single-phase grounding fault phase and the leading phase of the inter-phase grounding fault have aliasing region when the fault point is near the setting point. The large variation of the operation voltage of the non-fault phase is not conducive to distinguishing the two types of faults in the aliasing region, and thus the phase selection element is divided into low-resistance module and high-resistance module. The low-resistance module adopts the zero-sequence reactance line with the downward bias, which is used to identify the near-end and low-resistance short circuit. With the assistance of the low-resistance module, the high-resistance module only needs to deal with the faults near the setting point, which reduces the difficulty in distinguishing the two types of faults. After phase selection, the operation voltage before fault is obtained by non-fault phase polarization method, so as to determine the operation characteristics of the relay. The ability of high-resistance distance relay to withstand the transition resistance is far beyond the requirements of the regulations, which improves the selectivity of grounding backup protection to high-resistance faults. © 2024 Automation of Electric Power Systems Press. All rights reserved.