The Feasibility of Using a Vegetable Oil-Based Fluid as Electrical Insulating Oil

Esters of palm kernel oil have been synthesized and characterized for application as electrical insulating oil. Since such fluids serve both as insulants and coolants, tests were performed to characterize the chemical, physical and dielectric properties. Accelerated ageing tests were carried out to mimic conditions in a power transformer. Alkyl esters were synthesized from laboratory purified palm kernel oil: methyl ester was prepared through a transesterification reaction; an epoxidation reaction involving the methyl ester produced with insitu per-acetic acid in the presence of a catalyst to produce corresponding epoxy alkyl ester. This was then reacted with acid anhydrides under nitrogen in the presence of catalyst. This opened the epoxy rings of the epoxy alkyl oleate and linoleate components to attach side hydrocarbon chains. The characteristics and composition of the products were monitored using GC-MS and FTIR spectroscopy. The synthesized ester possessed a flash point that satisfied the specified minimum flash point for mineral oil, higher thermo-oxidative stability, and high and reliable breakdown strength from the distribution of breakdown data (43 kV/mm). It has a melting point of about -7˚C which is higher than mineral oil. An ester-paper sample which was aged in a pressure vessel under nitrogen and metal catalysts exhibited improved performance compared with the mineral oil-paper system. The rate of decrease in the tensile strength of alkyl ester-paper within the ageing condition was significantly lower than mineral oil-paper. Impregnation of cellulose paper with ester increased the charge storage capacity of the insulating paper. A strong low frequency dielectric dispersion (LFD) was observed which became more pronounced with ageing. Quasi-DC conduction was deduced to have dominated the low frequency response of alkyl ester-paper. The characteristic breakdown strength of the aged paper samples in comparison with the unaged sample did not show any significant difference. It is suggested that the synthesized ester is as good as mineral oil in many ways and a viable alternative fluid for cooling and insulating power transformers.