Abstract
Lightning is the main cause of transmission system outages, affecting reliability of power supply and resulting in economic losses. Shielding failure is an important issue in addressing the lightning performance of overhead transmission lines. In this paper an improved method based on the electro-geometric model is proposed to evaluate the shielding failure flashover rate (SFFOR) of transmission lines, considering the influences of landform, lightning polarity and stroke angle. In the improved method, the striking distances to phase conductors, shield wires and ground are properly differentiated by using recent equations developed to take into account other factors not only magnitude of lightning strokes. These factors include height of wires as well as lightning polarity. To reflect the effects of changes in terrain and height of wires on SFFOR, a method for identifying the topography and the relative position among the wires and ground is proposed. A 400-kV double-circuit transmission line section in complex terrain area was taken as example, and the results show that this method can reflect changes of the SFFOR along the span and can be useful to figure out which towers are easy to be struck by lightning along the entire transmission line. This research is helpful for the design and operation of overhead transmission lines.
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