An analysis of conventional grounding impedance based on the impulsive current distribution of a horizontal electrode

The performance of a grounding system should be evaluated in terms of the grounding impedance for a lightning surge containing high frequency components. The ground resistance is regarded as grounding impedance measured in a low frequency. When designing the grounding system, the grounding impedance and effective length should be considered. In this study, the conventional grounding impedance was measured as functions of the front time of the impulse current and the length of the horizontal electrode used largely as the grounding electrode of the transmission tower. In order to find the relation between the conventional grounding impedance and current distribution, the magnitude of the dispersed impulse current at every 10 m interval of the horizontal electrode, which is 50 m long, was measured and simulated as a function of the front time of the injected impulse current. The conventional grounding impedance was also measured and simulated as functions of the front time of the impulse current. The current distribution and grounding impedance for the first and second strokes were also examined. As a result, the conventional grounding impedance of a long horizontal electrode was similar to that of a short horizontal electrode for fast front time. As the front time of the injected current became shorter, the current distribution increased near the current injection point. In addition, the simulated results in the multi-layered soil structure were very similar to the measured results. In case of the second stroke containing high frequency components, the simulated conventional grounding impedance of the horizontal electrode was almost the same regardless of the length of the horizontal electrode being longer than 10 m since a large portion of the current was dispersed within 0–10 m section of the horizontal electrodes.

► Grounding performance should be evaluated by conventional grounding impedance under the lightning condition. ► We examined the relation between current dispersion and grounding impedance of horizontal electrode. ► The injected current with fast front time is largely dispersed near the current injection point. ► The conventional grounding impedance of a long horizontal electrode converged to that of a short horizontal electrode for fast front time. ► The effective length of the grounding electrodes should be determined by considering the front time of impulse currents.