A study of the degradation of cellulosic insulation materials in a power transformer. Part III: Degradation products of cellulose insulation paper

The cellulosic insulation materials in operational transformers undergo a slow thermal degradation during the life-time of the transformer to form furans which dissolve in the insulation oil of the transformer. There are six furans formed in significant quantity in an operational transformer. They are 2-furfuraldehyde, 5-hydroxymethyl-2-furfuraldehyde, 2-methyl-furfuraldehyde, 2-acetyl furan, 2-furoic acid and furfuryl alcohol. The concentrations of these furans can be measured by HPLC analysis of the oil. In this paper the furan products formed by accelerated ageing of cellulose insulation paper in Shell Diala B transformer insulation oil over the temperature range 130–170 °C are investigated, and the results have been correlated with those observed for the changes in the molecular weight and tensile strength of the insulation paper