A new algorithm for transformer ground fault protection

A new algorithm for transformer ground fault protection, also known as restricted ground fault protection, is presented. The algorithm is based on the phase comparison of the ground current and sum of the phase currents. By using a new digital phase comparator it is possible to identify presence of a transformer ground fault, thereby to reduce the probability of misoperations due to CT saturation during a ground fault outside protected zone. The algorithm is simple, fast, and reliable. Performance of the algorithm has been tested by using signals obtained by laboratory measurements and by the performed computer simulations. The paper presents the algorithm and results of the preformed tests.