What protection schemes are used for large synchronous generators?

Generator protection includes: differential protection (87G - primary for internal faults, compares terminal CTs), ground fault protection (64G - 95% stator ground, 100% with injection or third harmonic), loss of excitation (40 - detects underexcitation), reverse power/motoring (32), negative sequence/unbalance (46), out-of-step (78), stator overtemperature (49), generator-transformer overall differential (87GT), and backup distance/overcurrent. Protection is coordinated with turbine controls and excitation system. Generator protection relays (GPS type) combine multiple functions with oscillography.