Fault detection in multi fed underground secondary networks

Underground secondary networks in the urban areas are designed for 208 V, three phase and 120 V single phase loads. These cable connected systems with multiple transformer feeds are designed to supply heavy load requirements with a superior reliability. Since the cables are fed from various directions, there will be significant fault currents in the event of fault in the system. With aging and prolonged exposure to external environment, these cables develop faults. Some of the important type of faults are open circuit, single line to ground fault, double line to ground fault, three phase fault and high impedance faults. In this paper an approach is presented based on the three phase voltages, three phase currents, neutral voltage and neutral current to detect the various types of faults. The calculations are based on data from a practical system.