Dangerous pulse excitation of coupled lines

This paper studies a possible failure process for protection from high level pulses of equipment connected to multiconductor lines, dealing with multi-mode propagation on the lines, and the differences in the velocity of the various propagation modes on the lines. The damage mechanism is that a very short high level pulse may separate, due to the different modal velocities, into several lower level pulses at the location of the protection device, thus not triggering the protection, and then re-construct back into a higher level pulse further down the line, at the location of the vulnerable equipment. First, the essence of modal distortions is presented. Next, decomposition and restoration of a pulse in a structure consisting of two sections of multiconductor transmission lines are described. At last, the application of this phenomenon to power cables is shown