Influence of copper on the by-products and dielectric properties of different oil paper insulation

Transformer failure caused by the corrosion of copper material in transformer attracts great attention of researchers and engineers [1-2]. In this paper, 25# naphthenic transformer oil, 25# paraffinic transformer oil, Kraft paper and copper were used to compose four combinations of oil-paper insulation samples. The by-products resulted from thermal ageing processes at 130°C and changes in dielectric properties of the four combinations of oil-paper insulation samples were compared. The influence of copper on the by-products and dielectric properties of different oil-paper insulations was obtained. The results show that copper can accelerate the ageing rate of insulating oils and reduce their breakdown voltage. Copper has different effect on the furfural concentration in the naphthenic oil and paraffinic oil. The paper aged in the oil-paper insulation system with copper has higher moisture content than that without copper. The SEM results show that there is copper products depositing on the insulating paper surface. The insulation oil and paper aged with copper have higher dielectric loss and conductivity than that without copper.