Thermal ageing of oil-paper insulation

Detailed knowledge of the behavior of oil-paper insulating systems under accelerated thermal load is of interest in the operation of power transformers under increased electrical demands. The authors report on experiments on neutral kraft paper and naphthenic mineral insulating oil. These materials were aged in specially designed glass cells at 125, 140, and 155 degrees C for periods varying from 100 to 4000 h in a nitrogen atmosphere. Degradation was evaluated by mechanical tests (paper) and physical-chemical electrical tests (paper and oil). Results are presented and discussed. Of the physical-chemical and electrical tests carried out on insulating oil, only those on furfuraldehyde, water, and dissolved CO content gave good correlation with the DP (degree of polymerization) values of degraded paper.>