Influence of copper ions in transformer oil properties and adsorption treatment

The dissolution of copper with trace acid, oxygen, moisture, nitrogen compounds, and corrosive sulfur in oil formed copper ions. A transformer oil with 7.0 mg/kg copper ion was treated via the adsorption method. The efficiency of adsorbent was raised with the increase of addition amount and temperature. In the adsorption process, the copper ions, interfacial tension, water content, acid value, volume resistivity, and dielectric loss tangent tan δ of oil were tested, and the relationship between copper ions and electrical properties was investigated. In 140 h, the copper ions decreased to 0.5 mg/kg, the dielectric loss tangent from 2.19% to 0.07%, and the volume resistivity from 0.67×10¹² Ωcm to 7.05×10¹² Ωcm. Moreover, the antioxidant content, oxidation stability, and transformer insulation resistance before and after the adsorption treatment were analyzed. The adsorption treatment was effective in elevating the transformer insulation resistance from about one to ten thousand.