Improvement of particle-initiated DC flashover characteristics by using electrode and surface shapes in SF6 gas

To improve the withstand voltage under particle-contaminated conditions in SF₆ gas, the electrode and surface shapes of a spacer are changed simultaneously. It is shown that the breakdown voltage is considerably influenced by the distance from a particle to a rib. The characteristics are determined mainly by the field relaxation effect near the electrode and a long distance from a particle to a rib, and mainly by the barrier effect along the surface for a short distance. Therefore, it is desirable for high withstand performance under particle contaminated conditions that the electric field near the electrode decreases while keeping the barrier effect along the surface to some degree. In the case of a thick rib, the severest insulation condition takes plane when a particle is located at the rib top