Lightning is a main threat to transmission line safety.The existing works have studied the lightning risks leading to transmission line failures based on the factors like cloud-to-ground lightning density and so on.However

these methods do not consider the case that continuous lightning strikes the small area where many transmission lines converge.In this paper

a method is proposed for this situation.Firstly

a recursive algorithm is proposed to automatically identify the converging area from a large-scale transmission line network

which represents the transmission path.Then

the concept of unconditional or conditional multi-tripping event is defined.The number of each kind of events can reflect the tripping risk of the important transmission paths caused by continuous lightning.Taking the network made up of 25 transmission lines in Hubei Province and the data of lighting in 2013 for experiment

the proposed method is applied to get the transmission paths and the statistics of multi-tripping events of the transmission paths.Several typical cases are analyzed in detail for demonstration of the method.This study provides a new object and a calculating method for lightning damage prevention of power transmission grids.