Voltages induced on an overhead wire by lightning strikes to a nearby tall grounded object

The aim of this study was to identify conditions under which the presence of tall strike object can serve to increase or decrease lightning-induced voltages on a nearby overhead wire. We examined the ratios of magnitudes of lightning-induced voltages on the overhead wire for the cases of strikes to a tall object and to flat ground as a function of distance from the lightning channel d, current reflection coefficients at the top of the strike object rho_top and at the bottom of the strike object rho_bot, the current reflection coefficient at the channel base (in the case of strikes to flat ground) rho_gr, and the return stroke speed v. Lightning-induced voltages were computed using the finite-difference time-domain (FDTD) method. The transmission line (TL) model was used to find the distribution of current along the lightning channel and the strike object. The ratio of magnitudes of lightning-induced voltages for tall-object and flat-ground cases increases with increasing d (ranging from 40--200 m), decreasing rho_bot(<1), decreasing rho _top (<0, except for the case of rho_bot=0), and decreasing v (<c, speed of light). Also, the ratio increases with decreasing the lightning current rise time. Under realistic (expected) conditions such as rho_bot=1,rho_top=-0.5, and v=c/3, the ratio is larger than unity (the tall strike object serves to enhance lightning-induced voltages), but it becomes smaller than unity (the tall object serves to decrease lightning-induced voltages) under some special conditions, such as rho_bot=1,rho_top =0, and v=c