Dielectric properties of natural ester, synthetic ester Midel 7131 and mineral oil Diala D

Insulating liquids are widely used in high voltage industry applications which include the power stations, high voltage transformers and impulse power generators. Typical insulating liquids used in industry are mineral oils. In recent years, a large number of research papers have been published which focus on search for suitable liquid dielectrics to replace mineral oils and to achieve better dielectric performance. The dielectric performance of insulating liquids is a key factor which has to be considered in industrial design. Dielectric properties including ac breakdown voltage and mobility of charges are important parameters which characterize dielectric properties of liquid insulators. In this paper dielectric properties of synthetic ester, Midel 7131; mineral oil, Shell Diala D and basic vegetable (rapeseed) oil have been investigated. The ac breakdown voltages and the dc pre-breakdown currents have been obtained and an apparent mobility of charge carriers in these liquids has been calculated.