Frequency dependence of dielectric properties for water absorbed epoxy resin filled with silica

Composite insulating materials used in outdoor high voltage equipment are required to have high dielectric performance because of the miniaturization. The frequency dependence of the permittivity and the loss tangent have important information. In this paper we describe the frequency dependence of the permittivity and the loss tangent for water absorbed epoxy resin filled with silica and the influence of filler shape on the dielectric properties. A peak due to polarization appears in high frequency region over 1 MHz, and is caused by water absorbed in the resins. The increase of tan/spl delta/ in the low frequency region is caused by the increment of both of the electrical conductivity and the polarization due to the shape of filler and water absorbed in and near the interface between the fillers and resins.