International Symposium on Electromagnetic Compatibility zyxwvutsrqponmlkjihgfedcbaZYXWVU EMC'98 ROMA September 14 - 18, 1998, Rome, Italy 1-4 COUPLING EFFECTS AMONG AERIAL STRUCTURES AND EARTHED ELECTRODES IN A LIGHTNING PROTECTION SYSTEM G. Ala, P. Buccheri Dipartimento di Ingegneria Elettrica - Università di Palermo - viale delle Scienze, 90128 Palermo - Italia Abstract - This paper proposes a field-approach global model suitable for simultaneously evaluate electromagnetic contributions and mutuai influences of ali the elements of a lightning protection system (LPS). Simulation case studies of realistic LPS are illustrated. I. INTRODUCTION During a lighming discharge directly striking a building lightning protection system (LPS, Fig. 1), the realistic evaluation of the electric and magnetic fields inside the structure to be protected is a cruciai point in order to correctly estimate effects produced on circuits and apparatus in which undesirable coupling phenomena may generate abnormal signals and dangerous electric stresses on insulation of components. At the same time, it is of great importance, for the sake of human safety, the evaluation of the electric field transferred on separated embedded electrodes and on the ground surface, in order to make provision against the dangerous touch and step voltages which can be applied to human body (Fig. 2). such as pipe-work, staircases, elevator guide rails, ventilation, heating and air conditioning ducts. Usually, in technical literature, the evaluation of the above-mentioned currents distribution is carried out by means of numerical codes based whether on electromagnetic field approach [1] oron circuit models zyxwvuts AV AV =GC[ surface electric field < —> metallic pipe leakage current air-termination system nnq conductor down-conductor meshed earth electrode Fig. 1 - Lightning protection system of a building. For these analysis, it seems to be of basic importance the realistic prediction of the currents distributed in the aerial and embedded parts of the LPS and of reinforcing steel (which may carry part of the lighming current), as well as of the currents induced in metallic installations Fig. 2 - Dangerous voltages which may appear among metal installations connected to different points of the same grounding system of a LPS. in which the structure of LPS is modelled by an equivalent network of electromagnetically coupled elements [2]. In the latter simulation, the earth electrodes of the LPS are taken into account by employing conductive and inductive lumped parameters related only to earthed elements. The authors' opinion is that the electromagnetic interference between the aerial parts of the LPS and the earth electrodes system has to be investigated with greater care for the following reasons. At first, in agreement with the existing International Standards, the earth electrodes may be of complex shape and large dimensions: ring earth electrode integrated with vertical or inclined rods; complex mesh electrodes in the case of a building to be protected, in which an indoor electric power substation is installed. These latter earthing systems are not suitable to be modelled by employing lumped parameters which models only effects rising among embedded electrodes. In fact, also the circuit approach enables to guess that it is necessary a more careful evaluation of transient impedances and transferred effects on aerial parts and vice-versa. Afterwards, in calculating currents distributed along the aerial parts of the LPS, the real geometrical location and 360