Electromagnetic Fields of Accelerating Charges: Applications in Lightning Strikes to a Tall Tower

Abstract

The interaction of the lightning with a tall tower can be depicted by the electromagnetic field equations of a moving charge. When the equivalent moving charges are injected into the junction between the tip of tower and the bottom of lightning channel, they will travel both in the tall tower and in the channel. Along the channel, the charges will move with the return stoke speed and produce velocity field; but in the tower, they travel at the light speed without producing velocity field. At the both ends of a tower, the velocity of the moving charges will change, causing discontinuities here, and thus, the radiation fields will emit from the discontinuous ends. In such a process, the moving charges are experiencing repeatedly until the charges are fully exhausted by the channel and the ground. Based on this scenario, in this article, we proposed a method to derive the electromagnetic field radiate from the tall tower and also its current distribution by inputting the quantities of moving charges, the moving speed in the channel, the reflection and the transmission coefficient at the ends of the tower. To test the effectiveness of our method, we predict both the near-field and far-field from the tall tower struck by the lightning with three different return stroke models, i.e., transmission line (TL) model, modified TL model with exponential current decay with height (MTLE) and modified TL model with linear current decay with height (MTLL). Here, the TL model considers the velocity field and the radiation field, while MTLL and MTLE also incorporate quasi-electrostatic field produced by charges detained in the channel. Our predicted results are found to be consistent with the results from other methods. In general, our method avoids the need to incorporate the effect of current discontinuities at the return stroke frontwave compared to the extended engineering model, and could be more feasible than antenna theory method.