A transmission line model for the coupling of active sources to underground multi-conductor systems

This paper presents a generalised model and its equivalent transmission line equations (ETLEs) for a theoretical description and calculation of the coupling of external an electromagnetic source to underground multi-conductor transmission systems. Though the model is developed by employing a series of mathematical transforms, its novel closed representations of the ETLEs are simple, intuitive and easily applied to analyse and predict the coupling and interference problems in many engineering applications. The earth conduction effect, earth surface boundary, and mutual coupling among multi-conductors, as well as the impressed fields are all taken into account simultaneously in the ETLEs with equivalent transmission parameters. In the finite length situation where the transmission systems are terminated with arbitrary passive impedance between the earth and conductors, this model is still valid if the boundary conditions are taken into account when solving those ETLEs. An application of this model to conductive coupling to a two underground conductor system is also discussed. The results are in good agreement with the experiment