Influence of contact layer on the sulphur corrosion of copper conductors in power transformers

Abstract

Owing to the corrosive sulphides in the mineral insulating oil such as dibenzyl disulphide (DBDS), copper windings in oil-immersed transformers may suffer sulphur corrosion. This study investigates the influence of different contact conditions on the corrosion of copper conductors in transformers. Oil-immersed accelerated corrosion experiment was conducted on copper conductors with various contact materials and different layers of insulating paper. The surface micromorphology, deposition component and the potentiodynamic polarization characteristics of copper conductors were explored. The results show that copper with different contact materials suffer sulphur corrosion; conversely, bare copper rarely does. It was also verified that the existence of a particular gap between copper and contact layer is a significant factor in sulphur corrosion by the formation of a concentration cell on the copper surface. The insulating paper wrapped around copper conductors does not increase the corrosion tendency of copper; however, it contributes to the formation of a region concentrated with DBDS, Cu2+, H+ by adsorption and impediment, which plays a key role in facilitating the sulphur corrosion of copper conductors. Moreover, sulphur corrosion can also occur on other metal parts in transformers when there is a particular gap on surfaces other than copper.