Resistivity of pressboard immersed in mineral insulation oil

The pressboard is an important solid insulation dielectric in AC-DC converter transformers. Thus, it is very significant to understand the dielectric properties of the oil-impregnated pressboard. In this paper, the volume resistivities of oil-impregnated pressboard under different conditions have been systematically investigated. The pressboard was immersed in two kinds of mineral insulation oil, respectively. The measuring device of resistivity was full of oil and isolated from outside. All samples were measured at temperature range of 25-80°C under the field strength range of 1-30kV/mm. The influences of the temperature and the field strength on the resistivity of oil-impregnated pressboard have been investigated. The results of the volume resistivity of oil-impregnated pressboard showed that the resistivity of oil-impregnated pressboard decreased with the increase of temperature, and the activation eneregy increased with the increase of field strength. Meanwhile, with the increase of field strength, the resistivity changed slightly at first and then decreased significantly.