Dielectric Losses in Solid-Liquid Insulating Systems - Part II

A comparative study has been carried out on the dielectric loss behavior of polycarbonate cable models impregnated with a standard low-viscosity mineral oil and a silicone fluid within the same viscosity range. The importance of space-charge polarization at the interfaces of the well-defined solid-liquid boundaries of such insulating systems was demonstrated; large space-charge losses were found to characterize the mineral oil-polycarbonate combination used. In contrast, a closer match between the dielectric parameters of the polycarbonate plastic and the silicone fluid resulted in a low-loss insulating system, having desirable voltage stress and temperature characteristics. Impregnant contamination was observed to lead to extremely high losses, whose magnitude exceeded appreciably that found with kraft-paper cable models under identical contamination conditions.