Electric field control by polymer foam

For an improved design of high voltage apparatus a material with a low dielectric constant and a relatively high breakdown strength is advantageous. Therefore the insulating properties of polymer foam with closed pores are investigated. It was found, that for a foam with closed gas filled spheres the breakdown voltage is close to the partial discharge inception voltage and it depends on the void size and the degree of foaming. For practical applications a void diameter lower than 50 /spl mu/m in combination with a high gas content is desirable. The tested foam had a breakdown strength of 6 kV/mm and a relative dielectric constant of 1.1. Using this material a decrease of 30% of the size of high voltage electrodes can be achieved.