Abstract
Solubility of copper in insulating oil depends on sulfur contents and component of insulating oil. As increasing of sulfur contents, the solubility of copper becomes large. When being added di-tert-butylparacrezole and benzotriazole into the insulating oil, solubility of copper becomes small. Evolution of combustible gas is proportional to amount of copper in insulating oil, and type of gas pattern due to results of gas analysis in insulating oil depends on chemical component of insulating oil. In the case of low aromatic content oil, hydrocarbon gas evolves preferentially, but in the case of high aromatic content oil, hydrogen gas evolves preferentially. Although degradation of the insulating oil is effected by solution of copper, breakdown voltage of insulating paper is not falling down.
