A review on influencing factors of sulphur corrosion and metal passivation in power transformers

Corrosive sulphur compounds in mineral oil can react with the copper and silver surfaces in a power transformer which has been known to lead to failure. The metal sulphide layer may break off and be carried around the transformer by the flow of oil, and these particles then cause dielectric failure. The flaking of the metal sulphide layer exposes the new metal surface to further corrosion. To prevent this corrosion, passivators are widely added to the transformer oil. Most of the commercially available metal passivators are derivatives of Benzotriazole, which reacts with the metal surface creating a thin film passivation layer. Although these passivators are effective in preventing reactions with copper, there is some suspicion that silver surfaces are not protected. The main aim of this review article is to discuss influencing factors of sulphur corrosion and degradation of metal passivation layer.