Description of the discharge process in long air gaps under lightning impulse voltage

This paper presents high-resolution synchronous, electrical-optical measurements of lightning impulse discharge process in a representative 3 m air gap rod-plane configuration. The observed discharges can be differentiated in multiple sub-processes (streamer, backward wave and leader). We empirically analyze the characteristics and dependencies of these sub-processes and present a physical approach to model the lightning discharge. Reducing the discharge process to the inception and growth of the leader, the presented approach specifically describes the dependence of leader velocity not only on the leader current but also on the electric charge. The leader's required voltage and the conductivity of air gap are investigated as well. As a main contribution, the electrical discharge current can be calculated based on the instantaneous voltage and the determined conductivity of streamer and leader. As of yet, the presented model approach is not generic but limited to standard lightning voltage in rod-plane configurations up to 4 m gap distance.