New digital algorithm for distance relay

The value of the fault place impedance mainly depends on the design characteristics of the transmission line ground wire and towers footing resistance. The influence of the fault place grounding impedance in existing algorithms for ground fault distance relay is disregarded. Because of this approximation the distance evaluation is incorrect and the relay may misoperate. This is especially expressed in the case of the relatively short lines, as they are those in HV distribution networks. The development of the algorithm is based on the detailed consideration of all the return paths (ground wire, towers and substation grounding electrodes) of the ground fault current to its sources (the power system). The algorithm takes into account the main factors important for the accuracy of the distant estimation, i.e. fault place grounding impedance at fault place and fault current component coming from the opposite end of the line. Also, it is possible to take into account the influence of the arc at the fault place and the pre-fault current, although the influence of these factors cannot be considered as important for practice. The proposed algorithm was tested using simulated current data. Sample test results are also presented.