Investigation of lightning arc between conductor and nearby tree under artificial rainfall

In the Nordic countries, most distribution networks are installed in forest areas. Direct strokes to a tree can cause severe damage to nearby power lines by initiating an arc channel through air to bare conductors. In this paper, this phenomenon is examined experimentally using a full-scale laboratory setup considering dry-air and wet-air conditions, and the experimental results were reproduced by computer simulations. In a number of the experimental runs performed, it was found that the conducting arc path allows the establishment of a large long-duration lightning current from the lightning-struck tree to the bare conductor under the wet-air condition. Consequently, a higher induced voltage is measured on the conductor. The lightning-triggered arc phenomenon was monitored closely. It was confirm that lightning strokes to a nearby tree can be more intense in the wet-air than in dry-air conditions, and cause a flashover on power lines. The ATP/EMTP computer simulation using the arc model shows that the experimental results, one of which has been photographed and reported in the paper, are reproducible by means of system modeling. Both the experimental and simulation results provide strong evidence confirming the phenomenon of the arc conduction and the induced voltages due to lightning strokes to nearby trees within the vicinity of power conductors. Using a Rusck model, the study is extended to evaluate the induced voltage from the tree to the power conductor for larger clearances.