① Oil sample testing – Performance indicators such as withstand voltage and impurities should be tested every three years. For transformers operating at full or overload for extended periods, the interval can be shortened.
② High and low voltage insulation resistance should not be lower than 70% of the original factory value (10MΩ). The difference in the average value of the three phases of the winding DC resistance at the same temperature should not exceed 2%, and should not exceed 2% compared to the previous measurement.
③ Transformer working grounding resistance should be measured every two years.
④ The frequency of power outage cleaning and inspection should be determined based on the surrounding environment and load conditions, generally every six months to one year. Main contents include: removing defects found during inspections, cleaning the porcelain bushing casing, replacing cracked or aged gaskets, checking and tightening connection points, replenishing oil when insufficient, and checking and replacing the breather silicone sealant, etc.
