Electrical insulation diagnostic method and maintenance criteria for oil-immersed power transformers

This paper describes the findings of studying some criteria for diagnosis and maintenance control of oil-immersed power transformer through a gas-in-oil analysis, based on the results of sampling and measuring the insulating oils out of 1,324 transformers in practical operation. At the same time, furthermore, this paper summarizes the flow electrification characteristics in a transformer and proposes the limit value of determinant indicators for the charging tendency of an insulating oil and for a leakage current of transformer winding. In addition, a technique to diagnose the insulation degradation of an oil-immersed power transformer was also studied, thereby proposing an operating life determinant criterion.