Analysis on the causes of high lightning trip-out rate on electric transmission lines

• According to the findings presented in this article, when the lightning strikes the center of overhead ground wire between two towers, the assumption of a reflection coefficient of -1 specified in engineering practice is not entirely accurate. It is recommended that this situation be modified. • In deep canyon regions, thunderclouds may pass beneath high-voltage transmission lines, thereby creating conditions conducive to lightning strikes on these lines. • Traditional two-dimensional and three-dimensional are inapplicable or need adaptation for this deep canyon topography. The specific reasons are as described in Chapter 3 of this article. The causes of frequent lightning trip-out on transmission lines are complex and involve multiple interacting factors. In particular, high-voltage long-distance transmission lines operating in complex terrains are exposed to a markedly higher risk of lightning-induced outages. In this study, a wave reflection analysis is employed to investigate lightning performance under high soil resistivity conditions. The results indicate that when a lightning strike occurs at the midpoint of the overhead ground wire between two adjacent towers, the air gap between the overhead ground wire and the phase conductor becomes highly susceptible to back-flashover overvoltage, leading to localized flashover. Furthermore, a modified electrogeometric model tailored for canyon terrains is proposed and applied to representative engineering cases. The analysis shows that the risk of lightning shielding failure for high-voltage transmission lines in canyon areas increases significantly when canyon-depth effects are taken into account. These findings highlight that complex site conditions, such as high soil resistivity and canyon topography, should be explicitly considered in the lightning protection design of high-voltage long-distance transmission lines.