A High Speed, Discriminating Generator Loss of Excitation Protection

A new loss of excitation protection scheme has been devised in order to minimize the system voltage disturbance caused by excitation failure. It was designed specifically to prevent tripping of a sensitive load adjacent to a generating station with only one unit in operation. Besides meeting the special requirements of the single unit environment, the scheme appears to have some advantage over conventional loss-of-field protection when used in a station with more than one unit in service. The relay described has been in service for two years, complementing conventional protection, at a large nuclear plant which now has three units in operation. The relay is being modified to include limited over-excitation protection for future applications.