Santaldih Thermal Power Station of West Bengal Power Development Corporation Limited is a power station with an installed capacity of 500 MW (2×250 MW). Unit#5 (250 MW) got tripped in the morning on 25.05.17 due to Generator 100% Stator earth fault protection. After necessary checking, again Unit was synchronized in the evening. But after 1:30 hrs, it was observed that shaft vibration went very higher side for some time. After that Unit load was increased to full loads i.e. 250 MW at night. Then an annunciation came regarding “GRP Stator slot Winding temperature high”. At that time, it was observed that one slot temperature reaches above 105 deg. Centigrade and also observed that most of the slots temperature was being maintained at higher side. Due to this reason, the load was decreased & necessary actions were taken (opened all Generator hydrogen cooler vents & one hydrogen gas cylinder was fed to increase the gas pressure). After taken above actions, slot temperatures started to decrease. After that, it was observed that there was a huge mismatch in current (approx 1000 amps) at R- phase with respect to other two Phases. But suddenly unit got tripped at around 01:12 Hrs on 26.05.2017 due to generator electrical protection (100% Stator earth fault) operated.