The treble-circuit transmission lines are widely used to increasing energy transportation efficiency and saving land. Because of symmetrical electric structure, the treble-circuit transmission lines suffer from lightning trip-out for more than one circuit in a lightning strike. In this paper, an analysis model for lightning performances of treble-circuit transmission line was established. A typical treble-circuit transmission line with abundant operating data was taken as analytic target. The

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... chnical economies of two lightning protection devices and four layout schemes were discussed. By setting insulator parallel gaps and surge arresters in one circuit of a treble-circuit transmission line to break the electric balance, the average lightning trip-out rate for more than one circuit flashing can be reduced by 50%. According to the analysis result of lightning performance, setting lightning protection devices selectively can improve its lightning performance effectively with lesser cost, which has a good technology and economy.