New one cycle, microprocessor based differential relay for transformer protection

Abstract

This paper presents a fully selective new one cycle microprocessor based differential relay for transformer protection. The relay was tested and was found to take care of maloperation due to inrush, current transformer (CT) saturation with internal fault, unsaturated CT with external fault, saturation of one CT with external (heavy through fault) or internal fault etc., without sacrificing the performance of the differential relay under genuine fault conditions. The relay behaviour has been extensively tested by arranged circuits for differential protection of tranformers in the laboratory for all above conditions.