Couplage entre le champ électromagnétique rayonné par un coup de foudre et une ligne de télécommunication aérienne ou enterrée

This paper describes the determination of the current induced by a lightning discharge on a telecommunications cable using a transmission line theory. The electromagnetic field due to the return stroke is calculated by modeling the channel by a vertical antenna situated above a perfectly conducting ground. The electromagnetic coupling to a telecommunications line is then determined by introducing the finite conductivity of the ground into the transmission line model. Examples are given for various positions of the lightning discharge with respect to telecommunications cable. A comparison with results obtained during the last experiment at Saint-Privat-d’Allier is also presented. To get the response of a buried cable the authors first determine the propagation constant and the primary parameters of the line. The reference for the voltage is also analysed. The authors show that the choice of the origin at the infinity allows to take into account the energy propagating in the ground parallel to the cable.