An initial study into silver corrosion in transformers following oil reclamation

The problem of corrosive sulfur is extremely well documented in the electrical power industry and to some extent remains a global problem. The presence of corrosive sulfur in transformers is widely reported as a cause of sudden and unexpected failure. Regeneration of transformer oil using a reactivating sorbent in the form of bauxite clays has proven effective in removal of oxidation products in transformer oils. Unfortunately, in some cases, increased levels of silver corrosion have been observed shortly after oil reclamation. It is, therefore, important to understand fully the chemistry occurring both during the oil reclamation and during silver corrosion. Once a fuller understanding of the causes of increased oil corrosivity is obtained, effective precautions can be taken to limit the formation of corrosive species, whilst minimizing the volume of oil wastage during reclamation. In this paper, the problem of silver corrosion is discussed. Initial results from corrosion tests using transformer oils are described, with particular attention paid to the analytical methods used. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDX) was found to be a good method of characterizing the topology and elemental composition of the corroded silver surface. In terms of the oil composition, x-ray fluorescence spectroscopy is a very effective method for monitoring total sulfur and copper content. It is anticipated that once corrosive species are identified from the buffer tank samples, it will be possible to target such species in future analyses, allowing the detection of corrosive species at very low concentrations.