An algorithm for directional earth-fault relay with no voltage inputs

In this paper an algorithm for directional earth-fault relay without voltage inputs is presented. This relay is intended for use in isolated neutral networks. For a reference quantity the algorithm does not use the zero sequence voltage, but phase currents since in isolated neutral system they vary only slightly when a phase-to-earth fault occurs. Instead of the phase angle between the zero-sequence voltage and current phasors, the integral of the product of the phase and zero-sequence current over one-half period of the signals is calculated. For this reason the algorithm has high speed of response. The algorithm detects not only the line containing a phase-to-earth fault but also the faulted phase.

► The method is based on digital phase comparison. ► The procedure is intended for use in isolated neutral networks. ► Instead of voltage as a reference quantity the algorithm uses phase currents. ► The algorithm detects the line that contains an earth-fault and faulted phase.