Comparison between synthetic ester and mineral oil impregnated transformer paper aging markers

For transformers in service, aging markers from cellulose in oil such as furans, water, methanol and acids are measured for diagnostic purposes. The content of these indicators, measured in oil, may therefore vary with load, temperature, solid and liquid insulation aging, as well as marker stability and evaporative loss. Correction factors estimating the level of the aging marker to a reference temperature would make the diagnostic more relevant. In this study, correction factors for temperature differences have been estimated for different aging markers in insulation systems impregnated with either mineral oil or synthetic ester. In the case of mineral oil based systems, we observe correction factors for water, methanol and furans in line with previously reported findings. On the other hand, for the synthetic ester system, novel correction factors for water and methanol are suggested while for furans, no temperature dependence was observed.