Fuzzy adaptive transmission line differential protection with improved stabilization for near-by transformer inrush cases

In this paper enhanced differential current protection scheme dedicated for HV transmission lines is described. The adaptive fuzzy relay scheme is proposed that combines strengths of both current and phase comparison protection criteria. The relay stabilization characteristic is adapted on-line 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 near-by transformer inrush currents cause saturation of CTs installed in the protected line. The performance of fuzzy protection scheme has been tested with the use of Real Time Digital Simulator (RTDS) and compared to the traditional solutions.