Performance analysis of natural esters as transformer liquid insulation — Coconut, castor and sesame oils

Due to the poor biodegradability, transformer mineral oil insulation is now slowly being replaced by natural esters and synthetic oil. However, prefect replacement to mineral oil has not been introduced yet because of the poor properties of such alternative oils, i.e. high conductivity, high pour point etc. This paper presents a comparison of chemical and electrical properties of three such alternative oils namely coconut, castor and sesame oil. Performance comparison with mineral oil has also been presented to check their suitability of using as transformer liquid insulation. In chemical properties acidity, viscosity and pour point were considered whereas complex capacitance, loss tangent, breakdown voltage and corona effects were compared in the electrical properties. For complex capacitance and loss tangent measurements Frequency Domain Dielectric Spectroscopy test was conducted. It was found that castor oil and sesame oil had the potential to use as an alternative liquid insulation for transformers. Further studies are recommended to improve some of the physical properties such as viscosity.