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

Abstract

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 biodegradability 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. • 11 proportion of blends of refined and monoester of palm kernel oil were elaborated. • Flash/fire point, viscosity, acidity and biodegradability level of each blend were investigated. • Choice of Optimal proportion using Simplex Lattice Design method in DesignExpert 13. • Optimal proportion 32.22% MEPKO and 67.78% RPKO, Viscosity of 17 cSt, close to that of mineral oil. • Neutralization number 0.04 mg KOH/g, Flash point 190 °C, Fire point 216 °C, Biodegradability 75%.