Transmission-line Return-stroke Model for Lightning Striking to Tall Towers Considering Upward Connecting Leader

We present here an engineering return-stroke model for lightning striking to tall towers with taking into account the presence of the upward connecting leader (UCL). The current distributions along the lightning channel and the tower are derived, and the resultant lightning electromagnetic fields with various lengths of UCL above tower are calculated via a transmission line model. Obtained results indicate the electric field has a shading effect showing that the field amplitude generated by lightning striking to tall towers is smaller than that to ground, and that this shading effect depends on the length of UCL. The shading effect of the electric field increases with the increase of the junction height above tower, but disappears when the observation distance exceeds a critical distance. Modeled results are also compared with their measured counterparts associated with lightning striking to the 600-m tall Canton Tower in the literature.