The Effect of Longitudinally Varying Soil Conductivity on the Ground-Mode Low-Frequency Propagation Parameters of Overhead Power Lines

An analysis is developed for the evaluation, at power frequencies, of the propagation parameters of an overhead line section suspended above a nonhomogeneous soil whose conductivity randomly varies along the line length. The line section is broken down into a number of homogeneous uniform elemental cells, the length and conductivity of each cell, as well as the total number of cells, being randomly generated. The main result of this research is that conductivity random fluctuations give rise to negligible variations of the wave propagation parameters being analyzed. This leads to the conclusion that the standard practice of assigning the soil, in each line section, a uniform conductivity equal to its average value, can be safely employed with no significant errors incurred. In addition, a perturbation theory approach is developed, allowing not only an interpretation of the computation results obtained, but providing also a clear understanding of the role played by the different variables pertaining to the problem.