Understanding dissolved gas analysis of ester liquids: An updated review of gas generated in ester liquid by stray gassing, thermal decomposition and electrical discharge

In the last twenty years, natural ester liquids have come into wider use. As with mineral oil, under normal operating conditions the ester liquid in transformers is not expected to produce gases. However ethane has frequently been observed without apparent fault activity (stray gassing) and other gases have been reported from routine analysis. Results from experimental study of the temperature, electrical discharges and light exposures influence on gas production in ester liquids are presented here. Thermal faults have also been reported as producing gas in ratios that differ from mineral oil. Pyrolysis studies are used to help understand the significance of different chemical structures and reveal that the quantities of gas generated by thermal faults in ester liquids is larger than that for mineral oil. A statistical study of results obtained in routine DGA to evaluate how this could affect caution and warning limit is also presented. Finally, preliminary results of a on-going study of decomposition under partial discharge and D1 discharge conditions are presented.