Charging mechanisms of polymer spacers electrically stressed in SF 6 environment

An attempt is made to elucidate the mechanisms causing charge accumulation on and inside insulating spacers. The experiments were conducted inside a glass cruciform vessel which could be evacuated to 10 ^-2 torr and had a maximum SF₆ working pressure of 2 bar. Cylindrical spacers of polytetrafluorethylene and polyethylene (diameter 20 mm, height 10 mm) were investigated. The charge accumulation on smooth-surfaced insulators was controlled by three mechanisms: dielectric polarization producing heterocharge, surface charge injection from the electrode, and bulk injection from the electrode. The charge accumulated was of the same polarity as the applied voltage. The rough-surfaced insulator produced charge distributions which had charge densities higher than those of the comparable smooth-surfaced insulator