INDONESIA

Abstract:- This paper reports experimental results on dielectric properties of mixture between conventional mineral oil and a natural ester made from palm oil. The experiment was done in attempt to find new type of liquid insulating material which excellent in dielectric properties and friendly to environment. The sample used are mixtures between mineral transformer oil (Shell Diala B) and methyl ester from palm oil. The content of ester in the mixture ranged from 0 to 100 %. The breakdown voltage, losses factor and dielectric constant as function of ester content and temperature were investigated. The values of acidity, viscosity and gassing tendencies are also presented. The experimental results showed that increasing the ester content in the mixtures enhanced the breakdown voltage and slightly increased the losses factor. A higher increase of dielectric losses factor was observed at higher temperature. The dielectric constant of the mixture was stable in the range of temperature from room temperature up to 100oC. Acidity as well as viscosity increased with the ester content. The viscosity decreased with temperature. Dissolved gas analysis indicated that the total combustible in the mixture are considerably lower than that threshold value for normal condition according to IEEE C57.104. Comparing the experimental results and values of several properties in standard such as ASTM D 3487, ASTM D 1289 and IEEE C57.104, the composition of 50 % ester content is a good mixture to be used as biodegradable insulating liquid. Key-Words:- mineral oil, methyl ester, temperature, ester content, dielectric properties, dissolved gas analysi