A New Current Differential Protection Scheme for Two-Terminal Transmission Lines

This paper describes a new current differential relay. A current differential plane is presented firstly to depict different system statuses. Two traditional current differential protection schemes are discussed by plotting their operating and restraint region in the current-differential plane. A relay characteristic with more appropriate operating and restraint region is plotted in the plane by analyzing the tolerances a current differential relay has. Based on the analysis, a new scheme of current differential protection is designed. It is tolerant of channel delay asymmetry, power system impedance nonhomogeneity and CT saturation. Finally we prove the relay performance using simulations. It enhances current differential relay performance without a significant increase in cost.