What protection systems are used for oil transformers?

Common protection includes differential protection for internal faults, Buchholz relay for gas accumulation in conservator types, sudden pressure or pressure relief devices, overcurrent and earth fault protection, winding and oil temperature alarms, and bushing monitoring where applicable. For larger units, online DGA or moisture monitoring may be added. Protection design coordinates with transformer impedance, system fault levels, and risk tolerance to trip quickly while avoiding nuisance operations.