Radio-interference fields in multiconductor overhead transmission lines

Up to the present, radio-interference fields in close proximity to multiconductor lines have been calculated, in the first instance, on the assumption that the system is lossless. The loss has been calculated subsequently, on the assumption that the theoretical mode distributions hold good. In view of the errors known to occur when this earlier method is used, the present paper describes a theory in which the losses are computed as an inherent part of the solution of the wave equation. The solution is based on the theory of natural modes. Due consideration is given to the choice of transform matrix for the noise-current density, and a suitable expression is derived. Numerical results derived by a digital computer are given for a number of practical problems. The effects of the soil resistivity, the frequency and the phase excitation are discussed. It is shown that the correct choice of phase excitation can help in reducing noise fields.