Dielectric properties measurements of oil immersed pressboard

Dielectric properties including relative permittivity, dielectric dissipation factor and dc resistivity has been used widely as a design parameter of insulation system. In measuring dielectric properties of oil immersed pressboard (OIP), we have to make some adaptations from IEC 60093 and IEC 60250 e.g. effect of electrode's weight. This paper is focused on study of permittivity and d.c. conductivity measurement of oil immersed pressboard (OIP). In this experiment, the dielectric interface configuration consisted of oil immersed pressboard operated under oil bath in a vacuum tight test vessel. The pressboard samples were placed on a grounded plane under live electrode. Rounded-cornered electrode with radius 3mm was used as live electrode. For this experiment, the solid and liquid dielectric were oil immersed transformerboard type B 3.1A with 2 mm thickness and operated under mineral oil bath, Nynas Nytro 4000x. The pressboard and mineral oil used in the experiment were in dry condition with moisture level <; 0.5% and <;5 ppm respectively. The test vessel, electrode system and test procedure for OIP were set up according to IEC 60093 and IEC 60250. We concluded that, first, relative permitivitty and dielectric dissipation factor of oil immersed pressboard are highly influenced by temperature. The change of dielectric dissipation factor is significant only for temperature ≥ 90°C. Second, the relative permitivitty and dielectric dissipation factor of pressboard do not depend on the electric field stress for range 0.125 kV/mm-5 kV/mm. Third, the calculation of effective surface area A for calculating relative permittivity and d.c. conductivity is not significant for B factor >; 0.83. Fourth, it was also found that electrode with pressure higher than 1.9 N/cm2 give enough pressure to prevent a thin oil layer that present on surface. Furthermore, the results could be used as a consideration on measuring the dielectric properties of oil immersed pressboard in compliment with IEC 60093 and IEC 60250.