Investigations into pre-discharges in a rod-plane gap under negative lightning impulse voltage

Results are reported of investigations into the influence of the space charge associated with impulse corona on the growth and direction of the leader in a rod-plane of 1.72 m with a negative-polarity lightning impulse voltage applied to the rod. The charge oscillograms show three distinct steps of 2.5, 5.0, and 8.0 μC, and these are attributed to the first corona and secondary discharges including leader development. In order to assess the effect of impulse corona space charge on the field distribution, field calculations with and without space charges were carried out using the charge simulation method. From the results of the calculations together with photographs taken of the discharge, attempts are made to explain the direction and growth of the leader in the gap