A transient fault detection technique with varying fault detection window of earth modes in unearthed MV systems

This paper presents a transient fault detection technique in unearthed medium voltage systems. The system is simulated by ATP/EMTP program. A suitable fault detection window is introduced. The window width is the most sensitive part in the transient period. It is varying according to fault characteristics. The average impedance of the earth mode is calculated from voltage and current earth modes in the window. Based on the amplitude of the impedance, the feeder is confirmed to be faulted or not. The setting of detection is proposed from the simulation results that cover different fault inception angles and fault resistances.