Is There Evidence of Transesterification of Cellulose in Ester Insulating Liquids

The life of cellulosic insulation is often described as the life of a transformer. Monitoring systems and procedures are designed to maximize the life of the cellulose and hence, the life of the transformer. Many laboratory tests have shown that cellulose degrades at a lower rate in ester-based insulating liquids than in mineral oils. One proposed theory for the enhanced stability is the transesterification reaction in which the carboxylic acid portion of the ester is hydrolyzed from the ester insulating liquid and reacted with the hydroxyl group on the cellulose. The long chain hydrocarbon group provides a hydrophobic barrier preventing water from hydrolyzing the cellulose. The transesterification reaction, and the evidence for it, will be discussed.