Earth return admittances and impedances of underground cables in non-homogeneous earth

The influence of the stratified earth on the admittances and impedances of underground multiconductor arrangements is examined here. The electromagnetic characteristics of the stratified earth are included in a rigorous solution of the electromagnetic field equations, leading to new expressions for the self and mutual ground admittances and impedances of underground conductors. The new expressions are implemented for both a single insulated conductor and a typical three-phase single-core cable arrangement in various two-layer earth configurations. The derived propagation characteristics are compared with the corresponding ones obtained either by an approximate approach or for the homogeneous earth case. Finally, the modal propagation characteristics calculated by the proposed method are used in the simulation of steady-state high-frequency responses in the modal domain.