A survey of aging characteristics of cellulose insulation in natural ester and mineral oil

The article makes a case for allowing higher temperatures in transformers filled with natural ester fluids. This article will first provide a review of data from aging studies performed on cellulose (both Kraft paper and pressboard) impregnated separately in mineral oil and BIOTEMP (ABB, USA), a high oleic sunflower based fluid. Next, possible mechanisms that explain the differences in aging behavior will be discussed. The article concludes with recommendations for new temperature limits for BIOTEMP-impregnated transformers in comparison with mineral-oil-impregnated transformers.

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