Measured impedance by distance relay elements in a single phase to ground fault

Distance relays are one of the mostly used protective devices in the transmission systems. These relays are used as the main and backup protective device. Fault resistance is a source of error for distance relays in the form of the measured impedance deviation from its actual value. This paper discusses the measured impedance by six elements of distance relay first zone in the case of a single phase to ground (AG) fault. This is done by presenting the measured impedance at the relaying point and the distance relay ideal tripping characteristic for each element. The variation of the ideal tripping characteristic due to the changes in the power system parameters is investigated.