A unique current differential based algorithm for protection of three-winding transformers and busbars

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 a scalar sum of current terminals 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 transformers, such as overvoltage, overfluxing and overload, since the algorithm considers 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 authors. The purpose of the paper is to establish the principle and the applicability of the algorithm in busbars and three-winding power transformers.