Low thermal fault gases of various natural monoesters and comparison with mineral oil

Natural ester oils began to be implemented in higher voltage of power transformer in 2002. Gases generated by such oils need to be examined in order to anticipate the use of dissolved gas analysis (DGA) method to diagnose the presence of faults in natural ester filled transformer in service. This paper deals with an analysis of the gas generations of natural monoesters of different molecular structures derived from palm and rice bran oils under localized and low thermal faults ranging from 200 to 300 °C. Types of gases and their generation rates at various temperature levels were investigated. An attempt is made to compare the gas generation tendency between tested oils and commercially available natural ester insulation oil reported in the previous literature as well as mineral oil. The phenomenon of ethane generation by fatty acid monoesters having C-C double bond in their hydrocarbon chains and those without C-C double bond are discussed. Due to the expectation of overheating temperature, the possible implementation of CO/CH 4 gas ratio is also evaluated.