Small-argument analytical expressions for the calculation of the ground-return impedance and admittance of underground cables

This paper proposes small-argument approximations for two closed-form equations that were recently derived for the calculation of the ground-return impedance and admittance of underground cables. The proposed expressions are shown to be accurate up to 1 MHz for a typical cable configuration and frequency-dependent ground parameters. Their accuracy is also demonstrated in the calculation of transients on underground cables taking as reference results obtained with more general formulations.