On low-frequency propagation on a buried wire covered by a conducting jacket

When a buried wire is jacketed by a high-quality insulation, the propagation constant for the TM mode may be an order of magnitude greater than that of the insulation and many orders of magnitude less than that of the surrounding conducting medium. This is a well-known result. It is shown here that if the conductivity (σ1) of the jacket is so large that σ1/ω∊ ≫ 1, then the propagation constant (k) approaches close to that (k2) of the external ground when σ1 is still several orders of magnitude less than (σ2) the conductivity of the ground. Whereas the voltage drop across the jacket is practically the entire voltage drop from the conductor to infinity for an insulating jacket, it is a negligible part of the drop when the jacket is a good conductor. This latter fact has an important impact when the results of theoretical models are compared with field data.