Insulating properties of vegetable oils and their blends

Nowadays researches on the viability of using vegetable-or plant-based oils in power transformers are gaining much attention due to the excellent biodegradability and good dielectric properties they possess. However, studies on their long-term ageing properties and improvement on their dielectric properties is still lacking. This paper reports laboratory studies carried out on 5 different vegetable oils and their blends to investigate their dielectric properties during accelerated thermal ageing. The samples were aged for 120 hours and their breakdown voltage, dissipation factor and oxidative stability investigated. The tradition mineral oil was also investigated in the same fashion for comparison purpose. Results revealed that the vegetable oils insignificant decrease in their dielectric properties. Blending of the oils improved their dielectric properties and oxidation stability. This finding thus suggests vegetable oils possess can good electrical performance during service. Furthermore blending of vegetable oils can be an effective way to improve their oxidation stability.