Coupling model and impedance calculation of the steel ground loops with proximity effect

This paper focuses on the coupling model and the coupling impedances between two circuits with a common ground of a steel plane. By adopting a two-dimensional (2-D) electromagnetic model, the influence of the skin and the proximity effects are considered. In the case of a strong proximity effect due to the exterior wires, the distribution of the electromagnetic field inside and outside a steel plane is analyzed, and an equivalent coupling circuit model of two circuits with a common steel plane is built. The analytical solution of the coupling impedances and its frequency characteristics are calculated based on the proposed model. The solution is validated by the numerical solutions and the measurement results in the frequency range of 40 Hz-15 M Hz. The influence of the proximity due to nearby wires is severe in high-frequency situations, and the internal impedance of the steel plane changes up to 100 times compared to that of the isolated steel plane