Thermal aging of oil insulation comparing conventional and thermally upgraded papers

The author reports on experiments on two conventional and four thermally upgraded kraft papers and on naphtenic mineral insulating oil. These materials were aged in specially designed glass cells at 125, 140, 155 and 170/spl deg/C, between 100 and 4000 hr, in a nitrogen atmosphere. Degradation was evaluated according to the tests on papers and oil. Thermally upgraded papers with lower nitrogen content showed the best initial mechanical properties, but they displayed lower mechanical and chemical stability during aging. It is shown that the lower the TI (temperature index), the greater the FAL (furfuraldehyde) evolution.