Wave Propagation Characteristics and Electromagnetic Transient Analysis of Underground Cable Systems Considering Frequency-Dependent Soil Properties

The accurate estimation of the influence of the imperfect earth on the propagation characteristics of conductors is a crucial issue in electromagnetic (EM) transient analysis. In this aspect, the frequency-dependence of the soil electrical properties should be also considered. The effects of the dispersion of soil electrical properties on EM propagation have been investigated mostly for overhead transmission lines. This article presents a detailed EM transient analysis of underground cable systems taking into consideration the frequency-dependent (FD) soil properties. A generalized earth formulation of cable earth return impedance and shunt admittance is adopted. Propagation characteristics and transient responses are calculated by using both FD soil models and constant soil properties, as well as approximate earth formulations, neglecting the influence of the imperfect earth on shunt admittances; significant differences are observed. Guidelines for the accurate evaluation of earth conduction effects on the transient performance of underground cable systems are also introduced.