The relationship between carbon oxides in oil and thermal aging degree of oil-paper insulation

The thermal aging is one of the main factors leading to degradation of oil-paper insulation. Carbon oxides dissolved in insulation oil mainly come from cellulose pyrolysis, which indicates that the carbon oxides in oil can be used to predict the thermal aging degree of oil-paper insulation in power transformer. In this paper, accelerated thermal aging test for oilpaper samples composed of conventional 25# mineral oil and ordinary Kraft paper were performed at 130°C. The changing laws of degree of polymerization (DP) of insulation paper and content of carbon oxides in oil with thermal aging time were analyzed. The relationships between DP of insulation paper and the content of CO, CO
₂
, CO+CO
₂
and CO
₂
/CO were also analyzed. The results show that DP of insulation paper decreases fast with time in early thermal aging stage and decreases slowly with time in late thermal aging stage. There is no significant quantitative relationship between the content of CO and DP, also CO
₂
/CO and DP. The content of CO
₂
and CO
₂
/CO both are significant linear correlation with DP, which are good indexes used to judge the thermal degree of impregnated insulation paper.