Based on the research of lightning stroke fault character discrimination method and lightning protection caIculation method for transmission lines, the analysis method of transmission line Iightning stroke trip-out fault is proposed in this paper. It includes 4 parts: collection and sorting of operation materials, information inquiry of Iightning activities, judgment and analysis of lightning stroke accident character, and Iightning protection performance caIculation. The value of fault analysis is looking for the potential law of lightning faults, through many times of lightning failure analysis. The conclusion will provide specific guidance and advice for lightning protection measure implementation. An example of lightning stroke fault analysis for once lightning trip-out fault of 750kV transmission line in the year of 2009 is given in this paper. According to the line and fault data provided by operating units, compared with the detection information of LLS, the lightning withstanding level of shielding failure and back flashover were calculated. This trip-out fault was caused by lightning shielding failure, and the lightning currents which might cause this fault were found out. Because of the high height and complex topographical feature of tower, the transmission lines in this area were easily to be stroke by shielding failure. And the outside line located on the slope need to be paid much more attention to the shielding failure protection.
