The practice of ground differential relaying

The basic concepts are presented of ground differential protection for transformers and generators. Ground differential relaying provides fast and sensitive ground fault protection for wye-connected and ground electrical power equipment such as rotating generators or power transformers. Because it is a differential system, there is no need to incorporate undesirable time delay or to sacrifice sensitivity for the sake of system coordination. The authors first explain ground differential relaying for power transformers and generators, and then explain the ground differential scheme using a commercially available product type relay. Finally, they illustrate a method of current transformer selection that will help better implementation of the ground differential scheme