Digital Differential Protection of Power Transformer using DFT Algorithm with CT Saturation Consideration

Day by day power system protection demands high accuracy and reliability against abnormal condition to reduce maloperation and improve the stability of a power system. In a power system, the transformer is a most important, costlier as well as complicated equipment with respect to other equipment. Effect of Current Transformer (CT) saturation is a major drawback in transformer differential protection even detection of CT saturation and compensation techniques is a complicated process. This paper presents detection of CT saturation on the basis of first order Full Cycle Discrete Fourier Transform (FCDFT) in power transformer protection. Various cases of magnetizing inrush condition, internal and external fault on power transformer are validated using proposed scheme. Also, the proposed algorithm is validated for various types of abnormal conditions of power transformer with mild and heavy CT saturation condition. The algorithm is designed to differentiate whether the CT saturates or not during external fault condition and it also provides fast response to initiating or block the trip signal.