Influence of rate of voltage rise on positive leader inception in long-air-gap discharge

Positive leader inception under different rates of voltage rise is a key element in physical modeling of dielectric breakdown of long air gaps and evolution of natural lightning. The leader inception phase comes first in long-air-gap discharge, including first corona, primary dark period, and second corona, which is also called “leader corona,” portending leader inception. The Les Renardières Group has stated that the primary dark period is determined by the electrode curvature, based on which no leader inception model currently in use considers the influence of the rate of the applied voltage. To determine whether that assertion is true, an experimental scheme is designed so that impulse voltages can be applied with a large range of rise rates. With an increasing rate of voltage rise, the test results clearly show the following: (i) the curves relating the injected charge and inception voltage of the first corona present regular differences; (ii) the duration of the primary dark period decreases exponentially; (iii) the leader inception voltage and the difference between the leader and first-corona inception voltages present decreasing trends. These findings indicate that the formation of the dark period is related to more than just the electrode curvature, which is just one cause but may not be the essential reason for the dark period. The present findings suggest that the rate at which the applied voltage rises impacts the physical process of the streamer-to-leader transition during the dark period.