Modeling of Gas-Insulated Lines buried in single and in two-layer earth

The accurate modeling of 3-phase Gas-Insulated Lines (GIL) buried directly into the earth is the objective of this paper. The frequency-dependent terms that correspond to the influence of the nonhomogeneous earth, of the SF₆/N₂ mixture insulator and of the skin effect are integrated in the per-unit length impedance and admittance matrices of the system. After a proper modal transformation, the modal propagation characteristics of the system are derived. Several parametric investigations are carried out for varying soil parameters and for different two-layer earth structures in order to evaluate the influence of each of these characteristics on the propagation properties of the GIL configuration.