Effects of Pyrolysis of Metal Passivator on Characteristics of Insulating Oil Under Thermal Condition

As a highly efficient antioxidant for oil-immersed transformers, adding benzotriazole and its derivatives to insulating oil is proved to be one of the most effective suppression methods for sulfur corrosion in transformers. However, high temperature during device operation may affect stability of metal passivator in oil. This study explores pyrolysis of metal passivator in oil and effect of its degradation on characteristics of insulating oil under thermal condition. Thermal ageing experiments on oil-paper insulation, both with and without varying concentrations of the metal passivators BTA, TTA, and Irgamet 39, are conducted to analyze oil property variations. These experimental findings, combined with molecular dynamics simulations of the pyrolysis of oil-passivator molecular systems, elucidate the pyrolysis and degradation mechanisms of metal passivators in oil from both macro and micro perspectives. Experiment results show pyrolysis and oxidation resistance of metal passivator in insulating oil depends on oil-paper insulation thermal ageing degree and dynamic change in passivator concentrations dissolved in oil, especially pyrolysis of passivator resulting in abnormal generation of stray gassing, further leading to misjudgment of DGA result. Combinational and complementary method of thermal ageing experiment and molecular simulation further elaborates effect of pyrolysis and oxidation resistance of metal passivator on characteristics of insulating oil under thermal condition.