Consideration on the relationship between dielectric breakdown voltage and water content in fatty acid esters

Recently, fatty acid esters synthesized from the natural oil obtained from plants have attracted much attention as an insulating oil from the viewpoint of environmental problems, fluidity, and greater resistance to dielectric breakdown than conventional mineral oil. In the present study, to clarify the reason for the superior moisture tolerance of fatty acid esters, the inter- and intramolecular movements of fatty acid esters and the situation of dissolved water in the esters are investigated using nuclear magnetic resonance (NMR) and infrared (IR) spectroscopic measurements and density functional theory (DFT) calculations; it became clear that water molecules in fatty acid esters are trapped by the ester group of fatty acid esters. This is why fatty acid esters have a higher moisture tolerance against electrical breakdown than mineral oil.