Over-Reaching Factor for Distance Relay with Mho Characteristic for Inter Phase faults

Fault resistance is a source of error for distance relays leading to deviation of the measured impedance from its actual value. The presence of the fault resistance not only leads to measured resistance deviation, but also affects the measured reactance. This would lead to either under-reaching or overreaching. This paper investigates the over-reaching aspect by defining over-reaching factor for Mho distance characteristic in the case of inter phase, phase to phase and three phase, faults. In addition, variation of this factor due to changes in the power system conditions is investigated.