Variation of surface flashover voltage in SF6 withpressure

Surface flashover characteristics of solid spacers in a rod-plane configuration have been investigated in SF₆, at pressures to 400 kPa, for switching impulse voltages to determine the effect of spacer, spacer materials and polarity of applied impulses. The effect of spacer material on the flashover voltage is not significant. For negative polarity impulses, the influence of the spacer is also insignificant. But for positive polarity impulses, at pressures <200 kPa, the spacer efficiency becomes >1.0. On the other hand, at pressures >200 kPa, the presence of the spacer drastically reduces the flashover voltage of the system. At about atmospheric pressure also, the spacer efficiency in air has been found to be >1.0, with the same electrode geometry