Experimental study on the positive upward leader inception condition of horizontal conductors

It is believed that the lightning strike point of a large scale structure is dominated by the conjunction of the downward stepped leader and the upward connecting leader. The average height of conductors of the UHV transmission line is above 100m, and there is rarely report on the observation of positive upward leader initiated from ground wires or large bundle conductors in lightning attachment process to UHV transmission lines. In this paper, a series of experiments were carried out in high voltage laboratory to investigate the positive upward leader initiated from the real scale ground wire and bundle conductors. The positive upward leader emerging from horizontal conductors is recorded by high speed camera and the corresponding current is measured by using a broadband digital acquisition device. The stabilization field of ground wires and bundle conductors is derived from experiment results. It is concluded that the grounding resistance has no impact on the stable leader initiation, and the positive continuous upward leader incepted from the large bundle conductor is more difficult than the ground wire.