High impedance fault detection in low voltage networks

High impedance faults are those with fault current magnitude similar to load currents. Experimental results were obtained that confirm operating experience that such faults can occur in the low voltage (600 V and below) underground distribution networks typically found in urban power systems. These faults produce current waveforms qualitatively similar to those found on overhead feeders, but quantitatively smaller. Loose connectors can produce similar, but cleaner current characteristics. Noisy loads remain a major impediment to reliable detection. Design and installation of an inexpensive prototype fault detector on the Seattle City Light street network is described.>