Subsurface Transformer Finish Systems

A finish system providing corrosion protection for subsurface transformers is exposed to severe and variable environmental conditions. For example, it can be subjected to temperatures as high as 125 °C, wet and dry soils, and soils´containing fertilizer, salt, and other chemicals which affect the resistivity and pH of the soil. The coating can also be subjected to severe cathodic and anodic disbonding conditions that result from electrochemical reactions caused by the presence of copper groundings and zinc or magnesium anodes. The advantages and disadvantages of several finish systems used for subsurface transformers are reviewed in their relationship to these severe environments.