Impact of Generalize Formulation for Computing Earth-return Impedance and Admittance in Transient Studies for Underground Transmission Lines

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This paper compares the application of generalized and simplified formulations to compute the impedance and earth return admittance of underground transmission lines across a wide frequency range. The analysis focuses on resistance, inductance, susceptance, and conductance parameters. The generalized formulation employed is based on comprehensive electromagnetic field solutions proposed by Xue et al. (2018). In contrast, the simplified formulas draw from those found in literature and used in ATP and PSCAD software. Upon comparing the results of these formulations, deviations were observed in all parameters, particularly at higher frequencies and with increased soil resistivity. The findings underscore the necessity of utilizing the generalized formulation for precise assessments in transient events, cautioning against exclusive reliance on electromagnetic transient programs due to the significant deviations observed.