Silver corrosion in transformers

Abstract

The impact of corrosive sulfur on high value assets such as transformers is widely reported and can be considered a global problem. A great deal of research and development is focused on the remediation of corrosive transformers and the mitigation of future corrosion. Regeneration of aged and or corrosive oil by filtration through bauxite clays is a common method for removal of polar molecules and many sulfurous compounds such as dibenzyl-disulfide (DBDS). This process is largely successful, although over the last several years, increased corrosion and even total failure of transformers has been linked with the reclamation process. In some cases, the corrosion associated with a recent reclamation is selective for silver rather than copper. By thoroughly understanding the chemistry occurring during aged oil reclamation, it will be possible to take appropriate measures to limit the formation of corrosive species during future reclamation and regeneration processes. There is a requirement to minimize the amount of oil wastage during reclamation for both environmental and commercial reasons. It is also important that any changes made to the reclamation process do not have a detrimental effect on the health and life-expectancy of the transformer. This paper describes studies carried out to track the total sulfur content of oil samples taken from two different locations (transformer main tank and reclamation rig buffer tank), at multiple time intervals during an oil reclamation procedure. By tracking the total sulfur content, it is possible to determine when and where maximum sulfur accumulation occurs, possibly indicating the best point at which a portion of oil should be disposed. Once a fuller understanding of the sulfur content is obtained, GC-MS will be used to gain a detailed understanding of the types of sulfurous species present in the oil.