Dielectric properties of silicone oil, natural ester, and mineral oil under accelerated thermal aging

This paper reports experimental results on dielectric properties of silicone, natural ester, and mineral oil under accelerated thermal ageing. Samples are conditioned to the same initial conditions through the heating at a temperature of 100 °C for 24 hours. A number of oil samples of silicone, natural ester, and mineral oil with volume of 800 ml were put in hermetical bottles where 10 paper insulation sheets inside. The bottles containing oil and paper samples were subjected to thermal aging at 120
^o
C and 150
^o
C. Dielectric measurement was done after aging time of 336 hours, 672 hours and 1008 hours. Several dielectric parameters such as breakdown voltage, water content, acidity, dissipation factor and relative permittivity were tested. The experimental results indicated that natural ester has higher breakdown voltage compared to mineral and silicone oil. However, it has higher water content and dielectric losses factor. Silicone oil showed highest DC resistivity due to low water content. Natural ester showed low DC resistivity as result of high water content.