Comparison of earth return approaches on modeling of underground cables

This paper investigates the differences that occur in the propagation characteristics of underground cables, calculated using two individual earth return approaches. The first approach assumes that the influence of the imperfect earth is taken into account only on the cable impedances, using the well known Pollaczek-Sunde earth return impedance formula, while in the second model new formulas for the earth return impedance as well as for the earth return admittance are used. From the comparison of the propagation characteristics of a single insulated cable obtained by the two approaches a critical frequency is proposed, showing a frequency limit for the use of the approximate formulation of Pollaczek-Sunde. Finally, the paper discusses the results of transient responses caclulated in the frequency domain for different cases.