Dielectric properties of natural ester oils used for transformer application under temperature variation

The common insulating oil used in oil-filled transformer applications is mineral oil. In recent years, significant attention has been paid to alternative insulating fluids such as synthetic and natural ester liquids. The natural ester liquid is considered to be the best substitute of mineral oil in future. In order to apply natural ester liquid in transformers safely, it is important to have detailed information on its dielectric properties and its performance should be proven to be comparatively at par with mineral oil. This paper mainly focuses on a comparative study of ac breakdown voltage, dielectric constant, dissipation factor (tan δ) and resistivity of five different types of natural ester liquid under a variation of temperature. The natural ester liquids used in this experiment are rice bran oil, palm oil, corn oil, sunflower oil and canola oil. Based on the results, the dielectric constant and resistivity of all types of natural ester oil decreased with the increase in temperature. However, the dissipation factor properties in this experiment increased with the increase in temperature. In general, among all types of natural ester oil, the canola-based ester oil has the best potential to replace the current transformer oil due to its good dielectric properties as shown in this paper.