The mechanism of gassing in power transformers

Gassing of oil is defined scientifically as the chemical decomposition of certain hydrocarbons, under the impact of electrical and thermal stress. Indeed, the homolytic breakdown of vulnerable covalent bonds generates both small and large free radicals. The small ones become gases dissolved in the oil, while the large fractions generate insoluble colloidal suspensions. Currently, the electrical power industry believes that the gassing of oil is caused solely by hidden incipient electrical failures. Consequently, these are detected and diagnosed by periodic dissolved gas analysis (DGA). This paper provides experimental evidence that the formation in service conditions of undetected oil-born decay products is a contributing factor to the gassing of oil.