CALCULATION OF THE INDUCED EFFECTS DUE TO A LIGHTNING-STROKE

A method for computing the effects of a direct lightning stroke on the protection system of an industrial building is presented. These effects are generally interferences on power and/or electronic circuits inside the building or high voltages induced between the down-conductors of the protection system and metal structures closeby which can cause disruptive discharges and be a danger to people. The proposed method is based on a 'circuit-approach'. The lightning protection system and the 'victim' circuits are simulated by means of an equivalent electrical network formed by resistances, inductances and capacitances, having all the branches coupled together. The lightning stroke is simulated by means of an ideal current source characterised by a pulse waveshape. Propagation phenomena are considered and the ionisation phenomena in the soil are taken into account by a nonlinear current-dependent electrical model, function of the electrode's shape and the ground resistivity. Two distinct points of impact of the lightning stroke to the protection system are considered. An analysis, in the frequency and in the time domain, of effects such as step voltages of emf induced on power cables, coaxial cables, and loops is performed. The results show that a lightning stroke to the above mentioned protection system can cause transient effects characterised by high peak values, and that the roof-centre is the point of the protection system where it is most convenient to install the air termination.