Comparison of coconut/sesame/castor oils and their blends for transformer insulation

Different vegetable oils have been tested and proven as alternatives to the transformer mineral oil since recent years. This paper presents a comparison of physical, chemical and electrical properties of coconut, sesame and castor oils and their blends. The tested properties were color, acidity, viscosity, pour point, Frequency Domain Dielectric Spectroscopy (FDS) and breakdown voltage. First, commercially available vegetable oils were neutralized and de-moisturized, and were tested. Then the oils and their blends were exposed to corona ageing for 120 hours and were tested again. It was found that physical, chemical and electrical properties of oil blends change depending on the ratios of mixtures. Due to corona aging, dielectric losses and conductivity of the vegetable oils were increased.