Correspondence: Approximation to Carson´s loss formulae

Discusses the calculation of inductances of transmission lines above nonideal ground based on the images of the conductors. The earth is assumed of finite conductivity but homogeneous. For this case Carson´s correction terms (1926) of the impedance are well known and widely used. Carson´s corrections are, however, expressed in the form of truncated series so that their evaluation normally requires the use of a small computer program. The author proposes an alternative solution to the problem. Recognizing that the flux in the earth is not in phase with the return current, an equivalent return path is proposed at a complex depth. This preserves the possibility of using images for practical calculations even though a complex depth or distance has no physical significance. The author shows a very simple formula equivalent to Carson´s equations, and establishes its usefulness by examining its accuracy.