A Novel Directional Relaying Scheme Using Superimposed Impedance Approach

Abstract

Directional relaying is an important feature of protective relays in situations where the fault current direction is not fixed. Many transmission networks, meshed distribution networks, and modern smart grids containing distributed generation (DG) units are examples of these situations. Subtracting voltage angle from current angle indicates the fault direction in common methods. However, this method shows inaccuracy in some special conditions. In this paper, a new method is introduced to detect the fault direction. The proposed method applies a novel criterion, which is called superimposed impedance. This criterion is derived from the instantaneous voltage and current samples in the power system and indicates the fault direction properly. The proposed method is tested on a sample network through simulating in PSCAD/EMTDC and the results are plotted in MATLAB. The simulation results show the accuracy and effectiveness of the proposed method for different types of faults in various conditions.