Comparison of low thermal fault gases of various fatty acid mono esters

Proven to be a good substitute for mineral oil as insulation in distribution transformer, natural ester oils have been implemented in higher voltage of power transformer since 2002. Gases generated by such oils need to be examined to diagnose the presence of faults in natural ester immersed transformer in service, based on dissolved gas analysis (DGA) method. In this paper, the gas generations of chemically modified natural esters which are palm fatty acid monoesters under low temperature overheating ranging from 200 to 300 °C were analyzed. Localized thermal faults were conducted to simulate the real condition in transformer operation. Experiment on several kinds of fatty acid monoesters with similar and different molecular structure as well as mineral oil were also performed for comparison. Types of gases, concentrations and their trend against temperature variation were investigated. The differences of generated gases between the fatty acid monoesters having C-C double bond in their molecular structure and those without C-C double bond are discussed. Comparison of the gas generation trend between tested oils and commercially available natural ester insulation oil reported in the previous literature, as well as mineral oil are also elaborated. The possibility of generating gas ratio method to expect the overheating temperature is also evaluated.