Dielectric properties and oxidation stability assessment of vegetable-based oils as insulation for power transformers

Abstract

This paper presents laboratory investigations on 5 different vegetable-based oils and their blends to examine their long-term performance vis-à-vis their dielectric properties and oxidation under thermal ageing. The vegetable-based oil samples investigated included Canola Oil, Coconut Oil, Olive Oil, Palm Olein Oil, Sesame Oil and blends of canola and olive oil of 3 different blend ratios. The samples were thermally aged and measurement of their dielectric properties, oxidation and physical properties were conducted. Findings from this study indicated that the vegetable-based oils samples experienced more degradation (ageing) and oxidation compared to the standard mineral oil but however they exhibited high dielectric strength. Among the vegetable-based oils samples, coconut and sesame oil samples were the most aged and possessed the lowest breakdown voltage, while olive was the least aged and most stable. Sesame and canola oils experienced the highest oxidation while olive and coconut oils experienced the least. Blending of the canola and olive oils improved their dielectric properties and oxidation by as much as 37%. The finding in this study suggests that some vegetable-based oils can have good long-term performance as insulating oils. In addition, the simple and cheap blending of such oils can improve their dielectric properties and oxidation.