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Effect of ground conductivity and permittivity on the mode propagation constants of an overhead transmission line Doench, Claus

Abstract

A general analytical method to derive the distributed circuit parameters and mode propagation constants for an n-conductor transmission line is developed. The analysis uses electromagnetic field concepts and the results are interpreted in terms of distributed circuit parameters. The procedure involves transforming the problem of the n-conductor line above a ground with finite conductivity into that of an n-conductor above a ground with infinite conductivity. Correction factors are added to account for the finite conductivity of the ground. The distributed circuit parameters thus calculated are used to calculate the mode propagation constants over a frequency range from 10 Hz to 1 MHz for values of ground conductivity varying between 1 mho/m and 10⁻⁵ mho/m and relative permittivity varying between 10 and 50. Numerical results for the distributed circuit parameters and mode propagation constants for a typical 500 kV single circuit transmission line and various ground conditions are given. The results show that one mode has a higher attenuation and a lower velocity than either of the other two modes, suggesting the zero sequence mode for a completely balanced system.

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