New distance protective relay with improved coverage for high-resistance earth faults

Distance-type protective equipment often has, for a variety of practical reasons, rather limited tolerance to high-resistance earth-fault conditions. In this paper, a new distance relay, which has increased resistive coverage, is described, and it is shown to possess a characteristic which varies so as to accommodate more closely the impedance measured for various prefault loading conditions. Complicated setting procedures are avoided, and the results of dynamic tests show that the accuracy of the measurement can be maintained. A high degree of immunity to balanced phenomena such as power swings and operation during faults not involving a particular phase is inherent to the new relays. The paper concludes with a presentation of results relating to an application involving a 220 kV line of unearthed construction.