Extension of Vance's closed-form approximation to calculate the ground admittance of multiconductor underground cable systems

Abstract In this paper, Vance's closed-form approximation for the ground admittance of a single underground cable is extended to represent three-phase underground cable systems. The proposed methodology considers Sunde's expression for the ground-return impedance calculation. The accuracy of the proposed extension is investigated taking as reference the generalized formulas of Xue et al. considering frequency-dependent soil parameters according to the Alipio-Visacro model. It is shown that the agreement between the approximate and generalized formulations is improved as the frequency increases. More importantly, it is shown that both methodologies lead to transient waveforms in good agreement for different types of excitation, different values of soil resistivity, and usual underground cable system configurations.