Robustness of distance relay applied for distribution feeders with Mho characteristic against inter phase fault resistance

This paper discusses the maximum fault resistance, which can be tolerated by a distance relay with Mho characteristic applied at the source node of a distribution feeder, in the case of inter phase, phase to phase and three phase, faults. This resistance is defined as the boundary fault resistance which is the boundary of the distance relay correct discrimination between in-zone and out-of-zone faults. The robustness criterion is defined based on the boundary fault resistance. In order to achieve this, the related equations are presented and the boundary fault resistance curve is introduced. The variation of the boundary fault resistance curve and the robustness criterion is investigated due to the changes in the network conditions.