Pre-charging effects on low probability DC flashover along insulating spacer surface

The flashover along insulating spacer surface occurred with probability under abrupt DC voltage application. A special test procedure has been proposed for the measurement of flashover voltage with low probability (LPFV), which is used as a minimum level for the comparison of cases with and without pre-charging. In the uniform field the surface of a cylindrical polytetrafluoroethylene (PTFE) spacer was charged by DC corona produced by an auxiliary needle. The flashover voltage was subject to relatively large statistical fluctuations. In the non-uniform field of a rod to plane electrode system the spacer charges were deposited by DC corona near the rod electrode. In this case LPFV showed small scattering and good reproducibility. The results could be interpreted with surface charge effects on predischarge conditions and flashover process, in which deposited charges could move along the surface to modify electric field and enhance surface conduction.