Copper-in-oil dissolution and copper-on-paper deposition behavior of mineral insulating oils

Copper-in-oil dissolution and copper-on-paper deposition may affect the insulation of oil-filled power transformers, shunt reactors and high voltage bushings. Dissolved copper increases the dielectric losses in oil, and copper deposition can dramatically increase insulating papers' conductivity. The available literature does not report researches where the mechanisms of dissolution of copper in oil and copper deposition on the surface of solid insulation (Kraft paper) have been elucidated. This study is aimed at the investigation of the tendency of some commercially available unused mineral oils of different compositions to dissolve copper and to deposit it in the cellulose phase. Different conditions of reaction, presence of oxidation inhibitor (of the hindered-phenols family), addition of triazole-type compound (used as corrosion inhibitor) and general oil properties were studied to investigate their influence on copper concentration in oil and onto paper after artificial aging in controlled conditions.