Ground-differential protection revisited

The use of ground differential for the protection of impedance-grounded transformers and generators has been increasing. Because of its inherent selectivity and speed of operation, ground differential provides excellent protection against ground faults within the grounded winding of the equipment. However, several factors should be considered when applying ground-differential protection to a power system. These factors include the type and ratings of the equipment being protected, whether it is a new installation or a retrofit project, and the type of relay being used. Both static or electromechanical relays may be applied for ground-differential-protection schemes on impedance-grounded transformers and generators. Each application should be evaluated regarding current transformer burden and saturation to ensure proper operation. The protection engineer should carefully consider the application factors to ensure that the desired level of protection is provided