Application of Directional relay in an Ungrounded Power System to Locate Single Line to Ground Fault

To locate the ground fault in an ungrounded power system is very difficult and challenging problem. The single phase to ground fault currents in these systems are much smaller than the required magnitude of ground fault detection devices to operate. It is also important to isolate the single phase to ground fault before restriking of second ground fault on the system to prevent a possible double phase to ground fault. Ungrounded power systems have an advantage of continue the operation with single phase to ground fault but it is also desirable and important to locate and isolate faulted feeder of the system. This paper addresses the potential of identifying faulted feeder by using a high sensitive directional relay which determines the fault current direction in the ungrounded power systems. A Matlab Simulink Model is developed for ungrounded 11 kV three feeder power system. Single phase to ground fault is created in each feeder and it is detected by directional relay.