Gas generation of cellulose insulation in palm fatty acid ester and mineral oil for life prediction marker in nitrogen-sealed transformers

A new apparatus was developed for sampling the headspace of a closed thermal aging vessel. The gas characteristics of insulating material aged in mineral oil and palm fatty acid ester (PFAE), a new biodegradable dielectric fluid for transformer, were compared with the gas chromatography method, in combination with the developed gas sampling apparatus. The entire volume (Ve) and the oil dissolved volume (Vo) of gases evolved in closed vessels were determined and analyzed. The results demonstrated that the ratio (Ve/Vo) remained the same as long as the gas space ratio did not change. Carbon oxides production rates from mineral oil impregnated insulating material aging at 151°C -168.5°C are 3.7-4.7 times those for PFAE impregnated material, which revealed that PFAE protected cellulose from degradation. The volume of carbon oxides (CO2+CO) or CO2 (ml/g) correlated well with the degree of polymerization of insulating paper. The results demonstrated that carbon oxides could become a life-prediction marker in nitrogen-sealed transformers.