The Practice of Ground Differential Relaying

This paper presents the basic concepts of ground differential protection for transformers and generators. It is an important but seldom used scheme. During low magnitude faults the scheme provides a high degree of sensitivity and quick response for minimum burning time. The scheme should also provide good performance at maximum fault levels. It may help minimize equipment repair and enhance system reliability. This paper illustrates a method of current transformer (CT) selection to help insure proper operation of the ground differential scheme.