Electrical breakdown of short non-uniform air gaps

The breakdown voltage of air in highly divergent electric fields in not very short gaps (a few mm and above) is typically higher for negative energisation compared to positive energisation. Volumetric negative space charge, created by attachment of electrons to electronegative molecules in the case of negative energisation, reduces the field in the vicinity of the sharp cathode, resulting in higher breakdown voltages. This paper investigates self-breakdown voltages in short, mm and sub-mm gaps formed by point and plane electrodes and filled with atmospheric air at pressures 0.5-3.5 atm (abs). It is expected that space charge effects will change self-breakdown voltages for positive and negative energisation modes resulting in their different functional behaviour as compared with larger inter-electrode gaps.