Influence of the copper ion on aging rate of oil–paper insulation in a power transformer

To identify the influence of copper ion on the aging rate of oil–paper insulation, accelerated thermal aging experiments on oil–paper insulation were designed and performed at two significant temperatures. A set of characteristic parameters, including dissolved gases, degree of polymerisation, furfural content, water content and acid number of oil, was tested. The experiments' results reveal that copper ion has a different influence on insulation paper and oil during the aging process of the insulation system. On the one hand, it delays the degradation of insulation paper, reducing the ratio of CO2/CO by about 11% at 80°C and by more than 50% at 130°C. On the other hand, copper ion promotes the oxidation of oil and thus accelerates the aging rate.