Improvement of environmental characteristics of natural monoesters for use as insulating liquid in power transformers

Natural esters have high viscosity in their triglyceride form. Transesterification reduces their viscosity but lowers their flash point. In this paper, we proposed an optimal blend of natural esters, having the better compromise between flash point and viscosity, for use in power transformers. Mixtures of two components, refined and methyl esters of palm kernel oil (RPKO and MEPKO), were investigated by simplex lattice design (SLD). For each sample, the viscosity, flash/fire points, neutralization number and biodegrad-ability in an aqueous environment were determined. The mixture flash point increases with triglyceride proportion. The adverse effects are viscosity rise and biodegradability reduction. Optimal combination i.e., 32.22 % of MEPKO and 67.78 % of RPKO, has a lower viscosity of 41.01 % compared to RPKO and flash point reduced by only 9.32%. Although optimal flash point is lower than the requirements for natural esters, it is much higher than mineral oils flash point, with a viscosity close to that of mineral oils and a high biodegradability. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).