Degradation of cellulosic insulation in power transformers. Part 2: formation of furan products in insulating oil

The analysis of furan degradation products in transformer oil provides a complementary technique to dissolved gas analysis for monitoring transformer condition. The main products of the ageing are 2-furfuryl alcohol, 2-furaldehyde (furfural), 2-acetylfuran and 5-methylfurfural and are formed from wood-based paper (containing lignin and hemicellulose), cotton-based paper and pure cotton linters in accelerated, laboratory experiments. Also, 5-hydroxy-methyl-cellulose was seen in the early stages of some experiments. The concentration of 2-furaldehyde (furfural) was found to be highest of all the products and the concentrations of all products increased exponentially with time to a maximum value and then decreased. The concentration of most products increased rapidly as the paper approached the end of its useful life, indicating that furfural analysis could provide a sensitive trouble-shooting tool for rapid ageing. All the furan products apart from 2-furfuryl alcohol are relatively stable in the oil, at temperatures up to 140°C