Computation of inception voltage and inception time of positive impulse corona in rod--plane gaps

A method is proposed for computing the inception voltage and time of the corona in air in rod-plane gaps under a positive switching impulse and ramp-shaped voltages. The method is based on the rate of natural production of free electrons in the atmosphere as a result of cosmic ray activity, local radioactivity or ultraviolet radiation from the sun. The computed inception voltages agree reasonably with those measured experimentally for different values of the steepness of the applied switching impulse and ramp-shaped voltages and also with those measured experimentally for a rod gap stressed by a switching impulse voltage. The method is applied to different rod-plane gaps with varying rod radius and gap spacing