Determination of the Nature and Paraffin Content in Mineral Transformer Oils

Mineral paraffinic oils, now considered for replacement of the dwindling naphthenic oils used in transformers, produce solid waxes at low temperature which can have detrimental effects on the transformer life. Since the electrical and chemical properties of both kinds of oil are almost identical, it is very difficult to determine the presence of paraffins in a sample of transformer oil. Several techniques including DSC, X-rays, and cloud point measurements were used for this purpose on paraffinic oils of different origins. The best simultaneous evaluation of the onset of crystallization and wax content is obtained by DSC.