A combined S‐transform and fuzzy expert system for phase selection in digital relaying

This paper presents a new approach for faulty phase selection in transmission line based on combined S‐transform and Fuzzy Expert System (FES). The S‐transform with complex window is used to generate S‐contours (time–frequency contours), which ‘time‐localizes’ the fault. Features such as standard deviation (sd) and change in energy (ce) of the S‐contours for half cycle post fault current samples are calculated and fuzzified with simple triangular membership function. The fuzzified inputs are fed to the FES and the corresponding fuzzy rule is fired to provide the output as “1” for faulty phase and ground involved and “0” for no‐fault. The proposed integrated approach is tested for all 11 types of shunt faults with a wide range of operating conditions of the power system network. For testing the robustness of the proposed technique, the same is applied for the faults created on experimental set up with different operating conditions and provides accurate results. The output from the FES shows the fastness of the proposed technique and thus suitable for online application.