MODIFIED FOURIER-TRANSFORM LIGHTNING SURGE ANALYSIS OF AN OVERHEAD LINE-UNDERGROUND COAXIAL (CV) CABLE SYSTEM .1. MODAL-ANALYSIS OF UNDERGROUND CABLES AND OVERHEAD LINES AND EFFECT OF SUBTERRANEAN WATER ON CABLE MODAL PROPAGATION CHARACTERISTICS

In the first part of this paper, the modal analysis of a CV undergroun d transmission system is investigated. A digital computer program is d eveloped 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 accumulat e in the ducts is demonstrated. In the second part, a digital computer program is developed to investigate the dependence of the transmissio n line parameters and their modal characteristics on the frequency (El evtr. Power Syst. Res., 31 (1994) 43-49). A 77 kV three-phase single c ircuit has been used as a test system for the program. The effect of i nclusion of the ground wire, for lightning surge investigations, on th e modal analysis is illustrated. The results are discussed in connecti on with the electromagnetic transients.