A unique transformer protection which eliminates over-voltage, over-fluxing, and CT saturation protection

The paper describes a new differential relay showing the possibility of using the vector difference as a restraint quantity, while keeping the vector sum as a differential quantity. The vector difference is between the largest incremental current and the vector sum of incremental currents of the other terminals. This is as compared with the existing algorithms that used scalar sum of current terminals for three winding transformer as a restraining quantity, which is somewhat arbitrary. This is as well as reducing the need to provide additional protection for abnormal operating conditions of a transformer, such as over-voltage, over-fluxing, and over-load since the algorithm consider these conditions inherently as an external fault. This paper is first of all concerned with the existing protection scheme and then with a new scheme proposed by the author. The purpose of the paper is to establish the principle and the applicability of the algorithm in a three winding transformer.