Due to the higher suspension height of large cross section

the ground shielding effective is weaker than the common section

large cross transmission lines are easily hit by lightning. In order to ensure the safe operation of power transmission

the lightning protection of large cross section must be specially designed. In this paper

a comprehensive lightning protection design has provided for the 220 kV electrical power transmission line project of Jing Gangshan hydropower station across Gan river section. By establishing the EMG 3 D electrical geometry model

the relationship between side lightning rod length and protection distance is analyzed and the transmission line shielding failure rate is calculated. By establishing lightning transient model

the influence of ground resistance and coupled ground line on lightning overvoltage is simulated and analyzed. It is shown that

when the length of side lightning rod on tower head is 3 m

the protection distance is 21 m;the shielding failure rate can be reduced 93.2% by installation of 1.2 m short side pins on the lines;reducing grounding resistance is the most direct and effective measure to reduce reverse overvoltage

but in high soil resistivity area reverse overvoltage can be reduced more effectively by setting up couplinggroundwire.