According to IEC 60156 standards, the breakdown voltage of insulating oil in operational transformers must be at least 30 kV / 2.5 mm across standard test electrodes. For newly filled or reclaimed oils, values exceeding 60-70 kV are expected. Insulating oil dropping below 30 kV must immediately undergo vacuum purification (degassing and dehydration).

A Buchholz relay is a mechanical and hydraulic protective device installed in the pipe between the oil conservator tank and the main transformer tank. When minor gas generation occurs due to winding short circuits or insulation degradation, the relay's upper float triggers an alarm. In the event of a sudden and violent oil surge caused by severe internal faults, the lower flap trips the high-voltage circuit breaker within milliseconds, protecting the transformer.

SF6 (Sulfur Hexafluoride) gas provides superior arc quenching and dielectric insulation. When the pressure gauge reaches the alarm threshold (typically 0.55 MPa), immediate leak detection and sealing inspections are conducted. If the pressure falls to the lockout level, breaker operation is automatically inhibited. At this stage, the system is controlled and de-energized to execute gas replenishment and gasket refurbishment.