A 'Collection Volume Method' for the placement of air terminals for the protection of structures against lightning

摘要

A new methodology, the Collection Volume Method, is given for the placement of lightning rods or "air terminals" for the protection of structures against lightning. Each air terminal is assigned an "attractive radius", which is calculated as a function of its height, radius of curvature, location on the structure, structure dimensions, and a set of site, atmospheric and lightning-related parameters. In a similar manner, an attractive radius is assigned to all "competing features" on the structure which can also capture a lightning strike, e.g., building edges, corners, parapets, flagpoles, lift motor rooms, etc. The calculations of the attractive radii also depend on the upward leader inception criterion employed, in the present case a critical breakdown field of ～3 MV/m over an effective space charge or corona radius of ～0.3m, both taken from laboratory experiments of previous investigations. The attractive radius computations involve three-dimensional calculations of the electrostatic field on the surface and immediately around the structure, i.e., the degree of electric field intensification created by the penetration of the structure into the ambient field of the thunderstorm. The structure is regarded as being protected if the combined attractive areas of the various air terminals overlap those of the competing features. The Collection Volume Method is shown to be a new, practical, physically based technique for the efficient placement of air terminals on structures. It can both complement and replace existing placement methods as the need arises.