Power line transmission and radiation

Abstract

A power line system consisting of multi-conductors above the ground is decomposed into a metal return (or balanced) and a ground return (unbalanced) circuit in terms of propagation modes. Power line radiation above the ground is sorted into two classes, transition radiation from discontinuities which takes place from a line of finite length and Čerenkov-like radiation from a ground return or unbalanced circuit due to the Earth's finite conductivity and dielectric properties. Čerenkov-like radiation is thought to be predominant and to be a main source origin of power line radiation and, therefore, is specifically discussed in this paper. The problem is reduced simply to wave propagation along an infinite wire above the ground, without taking into account line discontinuities and ionospheric effects. It is shown that a TEM-type wave of a ground return circuit at low frequencies virtually transfers to the principal TM wave of a surface waveguide at high frequencies, via a hybrid EH-type wave in an intermediate range of frequencies, i.e., ‘transition region’ with increasing frequency. Consequently, the attenuation characteristics of wave propagation, which should include radiation losses as well as ohmic losses in the wire and in the ground, possess a maximum and minimum at certain frequencies in the transition region. This is due to two reasons: one is that the Earth transfers to a dielectric from a conductor and the other is that the field concentrates more densely around the wire with increasing frequency. Experimental evidence of this phenomenon is also given.