Lightning-Induced Transients on Buried Shielded Transmission Lines

This paper is primarily concerned with the analysis of induced transient current and voltage surges on buried shielded transmission lines due to earth-conduction effects of nearby lightning discharges. An analytical method is presented in this paper to model the conductive coupling mechanisms in the earth and to determine the amount of coupling between a lightning discharge to ground and an earth-return transmission line. The transmission line is assumed to be a long straight horizontal coaxial cable with an inner shield and an outer armor, terminated on both ends with typical communication-equipment load impedances. The general case is considered here, in which the outermost conductor is not necessarily in perfect contact with the conducting earth, but has a contact impedance with the earth, as in cables with an outer dielectric covering for corrosion or water protection. Average lightning-channel conditions and a representative buriedcable geometry are examined. The results are conveniently displayed via several graphs of the time histories of the resulting transient current and voltage surges.