Effects of the pyrolysis of metal passivator on the characteristics of insulating oil under the thermal condition

As a high efficient antioxidant for oil-immersed transformers, adding benzotriazole and its derivatives to the insulating oil is proved to be one of the most effective suppression methods for sulfur corrosion in the transformers. However, high temperature during the device operation may affect the stability of metal passivator in the oil. This study explored the pyrolysis of metal passivator in the oil and the effect of its degradation on the characteristics of insulating oil under the thermal condition. The thermal ageing experiments of oil-paper insulation with and without different content metal passivator of BTA, TTA and Irgamet 39 were carried out to discuss the properties variation trend of oil, further combined with the molecular dynamics pyrolysis simulation of the mixed system of oil molecules and passivator molecules, the mechanism of metal passivator pyrolysis and degradation in the oil was discussed from macro and micro levels. The experiment results show that the pyrolysis and oxidation resistance of metal passivator in the insulating oil depends on the oil-paper insulation thermal ageing degree and the dynamic change in passivator concentrations dissolved in the oil, especially the pyrolysis of passivator resulting in the abnormal generation of stray gassing, further leading to the misjudgment of DGA result. The combinational and complementary method of the thermal ageing experiment and molecular simulation further elaborated the effect of the pyrolysis and oxidation resistance of metal passivator on the characteristics of insulating oil under the thermal condition.