Suppressive effect of metal deactivator on the corrosion sulfur of wrapped copper immersed in mineral insulation oil

It has been found that the presence of corrosive sulfur species in mineral insulation oil leads to a large number of failures in power transformers and shunt reactors. The method of adding metal deactivators particularly Irgamet 39TM into insulating oil is widely used to prevent the reaction of corrosive sulfur with copper by forming a passive film on the copper surface. Nevertheless, the influences of paper layers and atmospheric conditions on suppressive effect of metal deactivator are not clear. In this paper, the thermal aging tests in hermetic air and nitrogen conditions are separately designed to investigate the suppressive effect of Irgamet 39TM. Copper plates wrapped up in different number of paper layers are immersed in mineral oil samples with different Irgamet 39TM concentrations and aged at 150°C for 72 hours. the effectiveness of forming passivation layers is evaluated by analyzing the atomic concentration of nitrogen, oxygen and sulfur on copper surface using an X-ray photoelectron spectroscopy (XPS). It has been found that under nitrogen condition, the content of sulfur on copper surface increases with the number of paper layers, and the nitrogen content on the samples wrapped in paper is less than the ones unwrapped. While under air condition, compared to nitrogen condition, the content of sulfur on copper surface is greater. The results show that paper layers and atmosphere conditions have significant influence on the formation of passivation film.