The characteristics of the surface discharge on the covered conductor for distribution systems

In relation to the prevention of outages due to the contact of animals, plants, etc. in distribution systems, the authors studied on the characteristics of the surface discharge on the covered conductor when a grounded bird nest was in contact with the covered conductor and a lightning surge appeared. Experiments were conducted in the laboratory with a test line consisted of a covered conductor, an insulator and a tie wire. The tie wire was grounded and a lightning impulse voltage was applied to the conductor. The surface flashover voltage was measured with a damaged conductor. A knife trace passed through the conductor jacket was impressed artificially to simulate the actual condition. The surface flashover voltage was measured for the position of a knife trace. Experiments were conducted under dry or wet conditions. As a result, the polarity effect was observed. Then, the characteristics of the surface discharge propagation were observed. The propagation length of the surface discharge was measured with a nondamaged conductor. Furthermore, to clarify the behaviour of the surface discharge, streak photographs were taken by an image-converter camera