Simulation of Electric Space Charges in Cavities Located Inside Industrial Dielectrics

Having excellent dielectrical properties combined with other good physical properties, polymers are used today for the electrical insulation of underground high voltage power transmission cables. Considering the microscopic level, these dielectrics are not homogeneous. They have a structure of amorphous and crystalline regions and the junction between these regions is the host of hopping regions. Thus, this microscopic inhomogeneity is providing substantial space charge at this microscopic level. The existence of space charge offers an electric stress enhancement, which may reduce the lifetime of the whole material. Complementary, the electric strength of the HV/MV cable is affected by the presence of that cavities (voids) in the insulating region. In service, when the whole insulation is subjected to electrical, mechanical and thermal stress, these cavities may lead to a larger discontinuous region. This paper treats, by simulation, the combined effect of space charge and cavities on the electric field, electric potential and temperature distribution within solid insulation. The values of their magnitudes in cavities are calculated, enabling us to envisage if partial discharges appear in these weak parts.