Factors affecting the position of interception of an electrical discharge in a composite gap under positive impulses

The results of an experimental research concerning the factors affecting the position of interception of an electrical discharge in a composite gap when stressed by positive impulses are presented in this paper. The test arrangement consisted of a wooden container with a metallic plate as a bottom and a vertical rod at a variable distance. The container was filled up to a variable height with sand. Over the surface of the sand two grounded parallel wires were stretched at variable distances between them and from the surface. Positive impulses 2/40 μs were applied on the rod. The variation of the relative interception probability of the breakdowns to be intercepted by the wires, to the total breakdown probability has been investigated for different gap clearances, sand layer thicknesses, sand resistivities and distances between the grounded wires. The dependence of relative interception probability from the above factors is given in graphs and is commented on in the paper. Comparison of certain results provisions of lightning protection standards, it can be concluded that similar investigations should be interesting for longer gaps with arrangements properly simulating an actual lightning interception system