Analysis of Insulation Characteristics of Coconut Oil as an Alternative to the Liquid Insulation of Power Transformers

This paper presents the experimental results of a study, which has been carried out to analyze the insulation characteristics of coconut oil in order to check the suitability as the liquid insulation in power transformers. In this study dielectric response measurements were carried out in frequency domain at temperatures of 25degC, 50degC, 80degC. In addition, results of mineral oil samples were taken for comparison. Further, breakdown voltage was also measured on samples. Based on the results, relative permittivity and conductivity values were obtained at room temperature (25degC) and elevated temperatures. Finally, the activation energy values were calculated on each sample. The dielectric breakdown voltages of the five coconut oil samples were in the range of 9.3 kV to 18.4 kV, which should be above 50 kV according to the IEC60296 standard. Conductivity values of coconut oil at room temperature were in a range from 10^-11 to 10^-12 S, which is considerably higher than that of new mineral oil. These results imply that further purification is required to bring coconut oil to the required standard to use as an insulating medium in transformers. Effort was done to identify the effect of temperature on dielectric response measurements of oil insulation system and correlation of it with the conductivity. The activation energy of five coconut oil samples was around 0.1, which is less than that of mineral oil, i.e. 0.4. This implies that the increase of conductivity with temperature is considerably low in coconut oil, when comparing with mineral oil.