A Buchholz relay is a gas and oil operated protection device installed in the pipe between main tank and conservator of oil filled transformers. It detects internal faults such as winding short circuits, core faults or severe oil discharges. Slow gas accumulation from minor faults triggers an alarm, while a sudden oil surge caused by a major fault operates a trip contact. The relay provides early warning of developing problems and fast tripping for serious internal failures, thus limiting damage to the transformer and enhancing overall system safety.