Physical interpretation of inductive interference of power systems on communications circuits

A tutorial on the physical process by which power lines induce interference in neighbouring buried communications cables is presented. The discussion is based on the interpretation of existing models and a plausibility argument for the current distribution in the earth below a transmission line. This leads to a simple model for inductive coupling, which can be used to predict the inductive influence of lines without recourse to numerical evaluation. A new measure of the inductive influence of transmission lines is proposed, which is based on a large separation approximation to the mutual impedance and includes the effect of conductor height, earth resistivity and current sequence. (author)