Including Frequency-Dependent Soil Electrical Parameters on Lumped Transmission Line Model

Abstract

This paper investigates the effect of frequency-dependent (FD) soil electrical parameters (conductivity and relative permittivity) on the performance of an overhead transmission line (OHTL) subjected to different disturbances. For this purpose, the FD soils are included in the traditional Lumped Parameter Model (LPM), resulting in an improved model named FDLPM. This model incorporates both Skin and ground-return effects on the longitudinal impedance of the TL. The ground-return impedance is computed using Carson’s approach, assuming frequency-constant (FC) soil parameters, and Nakagawa’s approach taking FD soil parameters. For this analysis, a single-phase 100-km OHTL located on low conductive soils and subjected to an energization maneuver and lightning strikes are considered for the simulations. The longitudinal parameters are fitted with ten branches of RL circuits for a frequency range from 0.01 Hz to 1 MHz. Voltages at the open-receiving end are calculated for an energization maneuver and two lightning strikes. The simulation results demonstrated that ten branches of RL-circuit provide a good fitting in the longitudinal impedance in FDLPM. Results also indicated that FD soils have a notable impact when lightning strikes and Gaussian pulse (highfrequency range) are assumed, and the voltage peaks are lower than those calculated using FC soils. However, for the energization maneuver (low-frequency range), the difference in the peak values is negligible. The difference between the voltage peaks increases for high-resistive soils where the frequency effect is more pronounced due to the ground becoming more conductive with the increasing frequencies.