A negative-sequence based method for fault passage identification

Reliable fault indication is crucial in any distribution feeder management system. A distribution line protective device can use different algorithms to detect whether or not it is in the fault path. When the downstream fault involves all three phases, detection is typically easy to achieve and phase elements are sufficient. Single line to ground faults cannot always be treated in the same manner, as ground sources are prevalent throughout the grid. In these cases, directionality (achieved by voltage polarization) is required. However, the requirement of both current and voltage measurements could render the solution cost prohibitive. If voltage is not available, detection may fail. Hence, there is the need for a simple but reliable ground fault indicator which is based on current measurements solely. This paper proposes the use of negative-sequence current to achieve this purpose. It is inspired by the fact that there is only one source of negative-sequence currents in a radial system. The proposed settings were implemented in large scale in the city of Fort McMurray throughout ATCO Electric's DSCADA devices. Such inputs are used by the feeder automation system to reconfigure the system automatically in case of permanent outages.