Fuzzy Adaptive Transmission-Line Differential Relay Immune to CT Saturation

This paper presents an enhanced current differential protection scheme with fuzzy inference system (FIS) support for high-voltage transmission lines. The proposed adaptive fuzzy scheme combines strengths of current and phase comparison protection criteria. The relay stabilization characteristic is adapted online depending on the output of the fuzzy reasoning scheme supplied with information from the phase comparison unit. The resulting protection is characterized by improved selectivity for external fault cases as well as when nearby transformer inrush currents cause the saturation of current transformers installed in the protected line. The performance of the fuzzy protection scheme has been tested with the signals generated with the use of Alternative Transients Program-Electromagnetic Transients Program and compared to the traditional solutions.