Abstract: A technique for detecting high impedance faults on solidly grounded, wye connected distribution circuits is disclosed herein. This technique bases its detection on the status of the third harmonic current component in each three-phase line current of the distribution circuit and specifically by the change in the phase of any one of the components during a period when the phases of the other third harmonic components remain unchanged. AT the same time, the technique disclosed herein discriminates between high impedance faults and many of the normal system disturbances such as capacitor switching, line switching, fuse blowing and others.

Abstract: A technique for detecting high impedance faults on distribution circuits with delta connected loads is disclosed herein. This technique bases its detection on the status of the third harmonic component in each of the three-phase line currents of the distribution circuit and specifically on a predetermined minimum increase in the amplitude of any one of these components over a continuous predetermined period, whereby to discriminate between a true high impedance fault and a transient disturbance.