Transient Analysis of Transmission Towers: Influence of Grounding System Topologies

Inhalt:
This paper investigates the influence of the tower footing grounding system (GS) on the transient response of a tall transmission tower subjected to lightning strikes. For this purpose, a 115-m-high transmission tower located on two types of ground: frequency-dependent soil (FD) and perfect electric conductor (PEC). The simulations use full-wave electromagnetic software (FWES) FEKO/Altair Engineering(r) employing the numerical Method of Moments (MoM). Firstly, the current distribution along the tower metallic structure is investigated in the frequency domain. Then, the harmonic impedance of the transmission tower with two distinct GSs is analyzed. The differences are compared to the harmonic impedance of the tower located on the PEC ground. The potential rise (PR) developed by these two lightning currents is calculated in the time domain. The results have shown that the current tends to have a higher distribution in the legs of the tower body, being more pronounced as the frequency increases. The type of GS remarkably influences the harmonic impedance, especially the resonant peaks at high frequencies. The voltages developed due to lightning strikes have a pronounced difference when distinct arrangements of GS are employed at the tower foundation.