A directional current differential protection against CT saturation in two sides fed networks

A phase angle comparison method for detection of current-transformer (CT) saturation and stability against mis-operation on heavy external faults in numerical current differential relay is presented in this paper. The proposed directional criterion is based on comparison of line currents phase angle of two sides of the power transformer. Defined criterion can differentiate saturation condition from normal condition and various internal faults. The merit of this method is demonstrated by simulation of different faults and saturation conditions on a power transformer using ATP/EMTP software.