Earth-return impedance for the multi-layer case

A general solution for the earth-return impedance of overhead transmission lines in the multi-layer case is developed in the paper. The solution derived permits the earth-return path to be considered as several layers of differing resistivities, permittivities and permeabilities. In particular, the results are extended to cover a discrete approximation of continuously variable formations is illustrated with examples of exponential and linear variations of earth resistivity.