On Possible Influence of Corona Discharge on the Propagation Speed of Lightning Surges Along a Tall Grounded Object

In this article, we present a sensitivity analysis to show under what conditions corona on vertical conductors may become significant. A lightning strike to a 600-m-tall grounded metallic object (tower) on a perfectly conducting ground is simulated using the 2-D finite-difference time-domain (FDTD) method in the cylindrical coordinate system and taking into account corona discharge from the lateral surface of the object. The tall object is represented by a cylinder having a radius of 0.1, 1, or 5 m (these values are representative of tower top, not the entire tower), where the extent of radial corona is most significant. The corona discharge is represented by a radially expanding higher conductivity region around the tall object. The corona radius is largest (up to about 5 m) at the object top with no corona at its bottom. It follows from the FDTD simulations that the wavefront of lightning current surge can be distorted significantly and the apparent propagation speed can be reduced. The reduction in propagation speed becomes more significant as the magnitude of lightning current increases.