Numerical Simulation of Permissible Touch Voltages in Case of a Lightning Incidence

Abstract

When lightning strikes an outer lightning protection system, hazardous touch voltages may occur. The lightning strike itself can be composed of different current wave shapes, which are directly connected to the first and subsequent return strokes. These current impulses have different characteristics. The resulting touch voltage wave shape is related to two of those characteristics. One characteristic is the magnitude of the current. The touch voltage wave shape is linked proportionally to the current wave shape flowing to ground. The second characteristic is the steepness of the current impulse. The rate of current rise induces a touch voltage in the loop, formed by the human body, the down conductor and the ground. In case of lightning strike, limits for those voltages are not defined. In order to evaluate the threat for a human being regarding touch voltages, limits must be known. The main threat comes from the ventricular fibrillation of the heart. Standards define relations between current magnitude and duration or energies that can be handled by a human body. However, it is not clear how much current is drained through the human heart, when voltages get steeper and shorter in duration. A computer simulation of a human body is conducted to compare known integral electrical parameters with parameters from the literature. From these findings, limits on hazardous touch voltages are derived. The main focus lies on the energy consumption of the human body and the related energy turnover in the human heart as an integral value.