Analysis of the Dielectric and Physicochemical Performances of Thermally Aged Natural Monoester Insulating Liquids

Interest in natural esters has grown rapidly over the last four decades, due to environmental concerns and sustainability. Various vegetable oils have been proposed, and various natural esters are already produced industrially. However, it would be worth using locally available inedible natural esters. In tropical regions, the methyl esters of castor oil and palm kernel oil suit such a fate. Thus, this work presents the results of the dielectric, physicochemical, and thermofluidic characterization of these two monoesters after thermal aging. After thermal aging, the paper breakdown voltage (BDV) when dipped in methyl esters was greater than the BDV of paper dipped in mineral oil (MO). The oils’ dissipation factor and dielectric constant ranged in the order castor highest, followed by palm kernel and finally MO. UV absorbance and neutralization number revealed that castor oil better reacted to long-term thermal aging than palm kernel oil. As compared with MOs, natural monoesters produced fewer decay products than MO from 500 h of thermal aging. The observed behaviors were commented on with the evolution of the functional links through Fourier transformed infrared (FTIR) spectroscopy.