Impact of Propagation Modes on Overhead Lines Using Physically Consistent Earth-Return Parameters

This paper examines the propagation characteristics and transient responses of a 220 kV overhead transmission line (OHTL) under transposed and untransposed configurations. Three approaches for calculating earth-return parameters are compared: (i) Carson's classical formulation, (ii) Pettersson's model with constant soil parameters, and (iii) Pettersson's model with frequency-dependent soil parameters. The analysis considers homopolar and non-homopolar modes for the transposed OHTL and five modes for the untransposed OHTL, using soil resistivities of 100, 1000, and 10,000 Ω·m. For all cases, energization and lightning responses were analyzed and compared using PSCAD simulations. Results indicate notable differences in attenuation constants and phase velocities at high frequencies, revealing a threshold where attenuation trends shift depending on ground losses. Furthermore, lightning response analysis shows that incorporating ground losses reduces backflashover occurrences by enabling higher current distribution to adjacent towers through shield wires. These findings underscore the critical role of frequency-dependent modeling and accurate soil parameter characterization for analyzing transient and high-frequency phenomena in OHTLs.