Modified Fourier transform lightning surge analysis of an overhead line-underground coaxial (CV) cable system Part I. Modal analysis of underground cables and overhead lines and effect of subterranean water on cable modal propagation characteristics

Abstract

In the first part of this paper, the modal analysis of a CV underground transmission system is investigated. A digital computer program is developed and applied to 77 kV three-phase single and double circuits. The dependence of the velocity and attenuation characteristics of the natural modes of propagation on the frequency is illustrated and their considerable dependence on the subterranean water which may accumulate in the ducts is demonstrated. In the second part, a digital computer program is developed to investigate the dependence of the transmission line parameters and their modal characteristics on the frequency ( Electr. Power Syst. Res., 31 (1994) 43–49). A 77 kV three-phase single circuit has been used as a test system for the program. The effect of inclusion of the ground wire, for lightning surge investigations, on the modal analysis is illustrated. The results are discussed in connection with the electromagnetic transients.