Surge voltage and environmental electromagnetic field analysis for HV composite transmission tower under lightning strokes

In this paper, the surge voltages of grounding system for a 330 kV high voltage (HV) composite transmission tower under lightning strokes are comprehensively presented. An equivalent distributed parameter model of the tower is established to investigate the lightning overvoltage by using EMTP program. The distributed capacitances among the adjacent two layers of cross arms, the capacitances between the lines and grounding ladders are calculated by using three dimensional (3D) Finite Element Method (FEM). The wave impedances of the ground wire cross arm, grounding ladder, and metallic tower body are determined by using the analytic equations. The lightning overvoltage calculation and comparison are conducted considering the diverse grounding configurations, such as the single-, double-, and three-ladder grounding systems. The influence of the radius of the grounding ladder on the overvoltage characteristics is analyzed. The proper grounding ladder system is determined so that the voltage between ladder and transmission lines is less than the flashover initial voltage of the cross arm. In order to evaluate the electromagnetic environment around the tower, the induced electromagnetic field at the level of 1.5 m above the ground is computed by 3D FEM. The simulated results suggest that the electric field intensity is much greater than the safety threshold of electric field intensity around the transmission lines.