Coconut oil as an alternative to transformer oil

Abstract

The paper presents a study which has been carried out to use coconut oil as insulation in transformers. Among the important properties considered are the dielectric strength of coconut oil which corresponds to less than 20 kV for a 2.5 mm sphere gap and the pour point which is approximately 23°C. To retain the oil in liquid form at low temperatures, several pour point depressants were tried. Some of them depressed the pour point, but also lowered the dielectric strength and proved unsatisfactory. In order to have improved properties, a purified form of coconut oil was used in the investigation. In this, the free fatty acids have been neutralized (reduced to 0.02%). Deodorization by steam distillation at 200°C has removed odorizing and tasting compounds of lower boiling points. The moisture has been reduced by heating to over 100°C. The demoisturized coconut oil sample showed promising results. The dielectric strength improved to 60kV or even higher dependant on the moisture reduction of the sample. Since the distribution transformer tank (manufactured by Lanka Transformers Ltd) is a sealed container and oil is filled inside a vacuum chamber, moisture inclusion after manufacture is prevented. As an alternative to reducing the pour point, repeated experiments on the dielectric strength of solidified and partially solidified coconut oil samples were carried out, and it was found that solidification does not appear to have any adverse effect on the dielectric strength. Coconut oil solidifies without creating voids, keeping its dielectric strength unreduced. When exposed to heavy magnetic fields, oil with a higher unsaturated degree of fats may break but coconut oil having a very low degree of unsaturated fats, ensures consistent properties at heavy magnetic fields essential for insulating oils.