Development of a positive creeping discharge along an aerial insulated wire

In high‐voltage aerial distribution systems, the insulated cables are supported by the binding wire with the post insulator at the utility pole. When a lightning strike occurs in the neighborhood of the insulated cable in an aerial power distribution system, inductive lightning surges invade the central line of the cable. Then, creeping discharges develop along the cable surface from the binding wire tip at the same time as flashover of the post insulator at a supporting point of the cable. If the cable insulator has weak points such as pinholes, a malfunction near the cable supporting point may occur, with melting of the wire due to punch‐through breakdown. To prevent such accidents, it is important to clarify the mechanism of the creeping discharge along the insulated cable caused by the lightning strike. The polarity of creeping discharges depends on the polarity of the inductive lightning surges, and the extension length and aspect of the discharge differ greatly depending on the discharge polarity. The development of these creeping discharges is attributed to complicated behavior of the positive and negative electric charges. In the present study, we examined in detail the development of a positive creeping discharge along a wire surface by using a high‐speed image converter camera. This paper describes the mechanism of development of a positive creeping discharge based on the experimental results. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 20–29, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20997