Effect of electric field on sulfur corrosion deposition and its diffusion research in power transformers

Corrosive sulfur in transformer insulation oil will attack copper strip and this attack behavior leads to the appearance of semiconductor deposition Cu2S. This deposition reduces the insulation characteristic of winding greatly. The formation of deposition will be influenced by temperature, oxygen and other factors. The effect of electric field on the formation of deposition was investigated in this work. In addition, the deposition is formed mainly on the innermost paper surface which is close to copper conductor. Unfortunately, this deposition can migrate from innermost insulation paper to outermost paper layer due to concentration gradient. Thus, it is also very necessary to investigate the mechanism of migration. Diffusion dynamical model was established according to Fick's theory in order to investigate the deposition migration. The results show that electric field can accelerate the degree of corrosion, leading to the increase of deposition content. Electro-chemistry corrosion is considered as the main reason to this acceleration. The diffusion model of deposition between paper layers in winding can be established by Fick's second law.