Influence on heterogeneous earth layers parameters’ contrast on ground return impedance

Aerial electrical line’s impedances of ground return through heterogeneous and homogeneous grounds and their differences were calculated for the earth with different interlayer contrast of parameters for series thicknesses of the earth upper layer. Behavior of the impedance differences against changes of frequency and upper layer’s depth is investigated in the article. It was shown that the worst approach of relative differences to the zero takes place for the little thicknesses of the earth upper layer (less than 8 meters) and very high frequencies at which the impedance concept loses its certainty and physical meaning.