Protection against internal phase-to-earth faults when the system is earthed can be provided by restricted earth fault protection.
While not covering phase-to-phase faults this arrangement does have the advantage that individual phases of the generator do not have to be brought out at the neutral end.
It is usual to back-up restricted earth fault protection with an unrestricted earth fault relay energized from a single current transformer in the generator neutral.
This relay will respond to earth faults anywhere on the svstem and therefore it should be of the time delay type with current and time settings selected to give discrimination with feeder earth fault protection When neutral earthing resistors are employed an additional relay providing standby earth fault protection may also be used.
