Dielectric breakdown in high density helium and in helium impregnated solid dielectrics

An understanding of dielectric breakdown phenomena in high density helium and in helium impregnated solid dielectric is of importance in the development of superconducting electrical equipment. This investigation describes measurements of helium breakdown field which demonstrate its dependence on helium density. This dependence occurred in at least three distinct modes. The behaviour at helium densities > 100 kg m^-3, suggested to be characteristic of breakdown in high density liquid, is of particular interest. Results showing the dependence of breakdown field on helium pressure and on cathode material and surface condition are presented. Internal discharge inception voltages in helium filled cavities in polyethylene and epoxy resin are shown to depend not only on the density of the helium, the sample dimensions and permittivity of the solid, but also on cavity surface effects. © 1985.