Once upon time the Generator Transformer 22.8 kV / 525 kV shown Buchhozl relay alarm, and then check actual at location that accumulation gas appear on sight glass of buchholz relay.
The accumulation gasses on the transformer means the oil as cooling, isolation and dielectric has degradation of oil quality. The accumulation gasses as H2, CH4, C2H2, C2H4, C2H6, CO and CO2 so long so high and the Unit load got alarm level light when the accumulation gasses reach 350 cm3 as picture below this ( Unit trip at heavy categorize on gasses level > 550cm3.
Operator try to make the Unit electric produce more longer by vent that gasses but combustible gasses accumulation so long reach the danger level, so that we reduce the Unit load until operator can control that accumulation gasses, but it was useless.
The Unit must shutdown, but after Unit de-synchronize, the gasses on transformer buchholz relay still appear, so we had to de-energize the transformer.