An accurate knowledge of the per-unit length impedance of power cables isnecessary to correctly predict electromagnetic transients in power systems. Inparticular, skin, proximity, and ground return effects must be properlyestimated. In many applications, the medium that surrounds the cable is notuniform and can consist of multiple layers of different conductivity, such asdry and wet soil, water, or air. We introduce a multilayer ground model for therecently-proposed MoM-SO method, suitable to accurately predict ground returneffects in such scenarios. The proposed technique precisely accounts for skin,proximity, ground and tunnel effects, and is applicable to a variety of cableconfigurations, including underground and submarine cables. Numerical resultsshow that the proposed method is more accurate than analytic formulas typicallyemployed for transient analyses, and delivers an accuracy comparable to thefinite element method (FEM). With respect to FEM, however, MoM-SO is over 1000times faster, and can calculate the impedance of a submarine cable inside athree-layer medium in 0.10~s per frequency point.
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