An Innovative Directional Relaying Scheme Based on Postfault Current

Directional relaying is one of the most important features of protective relays in situations where the fault current direction is not fixed. Most transmission lines, meshed distribution networks, and modern smart grids, including dispersed generation (DG) units, are examples of these situations. Conventional directional relaying schemes have some shortcomings and cannot be used in all practical cases. The application of voltage as a reference quantity for the detection of fault direction is a common practice in transmission lines. Nevertheless, this approach is not applicable in distribution networks due to the absence of potential transformers. A recent solution is the application of prefault current, instead of voltage, as a reference quantity. However, this method requires the voltage for the detection of power-flow direction. In this paper, a novel directional relaying scheme is introduced which is able to detect the fault direction using only the postfault current. The proposed scheme overcomes all of the mentioned problems in conventional methods. The efficiency of the proposed scheme has been approved over extensive simulation studies in different operating conditions.