Improving Differential Relay Performance during Cross-Country Fault Using a Fuzzy Logic-based Control Algorithm

Abstract

This paper presents a fuzzy logic-based algorithm to improve the performance of the differential relay in short transmission line protection for Cross-Country faults. This type of faults leads to the malfunction of current differential relays, while the probability of the relay performance error becomes negligible by using a fuzzy logic system along with the changes in per-unit values and the slope of the differential relay, and consequently choosing the best stability characteristics. In the proposed algorithm, the sensitivity, operation reliability, and performance speed for several types of faults including internal faults and even the high-resistive faults are maintained in the satisfactory levels. The algorithm is also suitable for external faults with the saturation of current transformers (CTs), and it improves the relay performance. The effectiveness of the algorithm is verified in EMTDC/PSCAD software program, and the obtained results are compared with those of conventional methods.