Surface charging and flashover of spacers in SF6 under impulse voltages

The authors describe a series of experiments to study prebreakdown spacer charging and subsequent flashover in a compressed gas insulated rod-spacer-plane system under positive impulse voltages. Prebreakdown corona is identified as the most likely source for spacer charging. Surface charges were measured in situ with capacitive probes after the applied lightning impulse voltage had decayed to zero. Numerical computation of resultant electric fields, using the surface charge simulation method, shows that the electric field due to surface charges significantly lowers the electric field near the rod electrode but enhances the overall electric field over the rest of the spacer surface. The flashover voltage with a spacer is higher than for a rod-plane gap. A reversal of the applied impulse polarity may lower the flashover voltage for a rod-spacer-plane gap