The opportunities and risks of using a dynamic electro geometrical model in lightning protection

Inhalt:
The dynamic electro-geometrical model has become a famous method to calculate interception probabilities on arbitrary structures. Nowadays numerical approaches exist to to either speed up calculation and investigate even complex arrangements. Those approaches have led to the dynamic electro-geometrical model being used time and again to conduct iterative planning of lightning protection systems on buildings and installations. It turns out that with such planning approaches, the interception areas are calculated correctly, but the relative ratios from which the interception efficiencies are derived, can degenerate. This can result in lightning protection system that do not offer substantial lightning protection. The purpose of this paper is to investigate the calculation methodology behind the dynamic elctro-geometrical model and to point out its advantages and disadvantages, as well as its drawbacks, a planner should be aware of. Although the model is primarily aimed at calculating interception efficiencies, it is made clear that the dynamic electro-geometrical model is based on the calculation of interception areas. The model thus uses a parameter that is already used in other methods to either estimate the risk of a lightning strike to a structure or to estimate the number of shielding failures or back flashovers on transmission lines. Fictitious and exaggerated examples are chosen to illustrate similarities to other methods and also to show possible problems. Suggestions are made for improving the analysis in the future. The main methodology of the dynamic electro-geometrical model remains unchanged. The focus should be placed more on the interception areas and the maximum lightning peak currents, similar to what is done when evaluating the lightning performance of transmission lines and the risk assessment in the lightning protection standard, where absolute vales like the number of strikes or dangerous events are calculated.