Lightning currents coupling to metal tubes

Signal and control cables are often placed in closed metal tubes for optimal protection from induced overvoltages in case of lightning. The key parameter is the current distribution along the tube, which is closely related to the currents flowing through the earthings to which the tube is connected. A careful analysis of the current distribution has to be made prior to the coupling study. A computer model based on electromagnetic field theory, which takes into account the interactions between different parts of the conductors is described. The distribution of the current is assessed in both frequency and time domains. The influence of a shield wire placed near the tube is also analyzed