Adaptive earth fault distance relay

Based on case of single-phase-to-ground fault, this paper derives the combined error of measured reactance in proportion to the distance to the fault, and provides a new adaptive impedance criterion through error correction. A new reactance line in the polygon impedance characteristic of the proposed criterion is suggested to replace the declinational reactance line. This does not need to reduce the protection zone any more as conventional way to prevent the relay from overreaching. The protection zone of the proposed distance relay is greatly increased without any danger of mal-operation. The performance of the relay is extensively tested by using EMTP. The simulation results show that the relay can be used to avoid transient overreaching effectively and has high sensitivity for the internal fault.