Effects of negative direct voltage pre-stressing on the breakdown of conductor-rod gaps under positive impulse voltages

The sparkover of a 50 cm conductor rod gap under positive impulses is investigated when a pre-stressing negative direct voltage is applied to the rod. Under lightning impulses the pre-stress has a small effect on the breakdown voltage of the gap. For long-front impulses, a considerable increase in the dielectric strength of the gap can be observed. Several parameters affect this behaviour, like the value of the prestressing direct voltage, the diameter of the energised conductor, the position of the rod with regard to the conductor and the waveshape of the applied impulse