AN ANALYSIS OF CONVENTIONAL GROUNDING IMPEDANCE BASED ON THE IMPULSIVE CURRENT DISTRIBUTION OF A COUNTERPOISE

The performance of a grounding system should be evaluated in terms of the grounding impedance for a lightning surge containing high frequency components. Grounding impedance shows resistive, capacitive and inductive behaviors. Ground resistance is regarded as a particular grounding impedance measured in a low frequency range. When designing the grounding system, the grounding impedance and effective length should be considered. In this study, conventional grounding impedance is measured as functions of the front time of the impulse current and the length of the counterpoise 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 along of the counterpoise, which is 50 m long, is measured and simulated according to the front time of the injected impulse current. As a result, the conventional grounding impedance of a long counterpoise is similar to that of a short counterpoise with a smaller front time. As the front time of the injected current becomes short, the current distribution is increased near the current injection point. In addition, the simulated results of multi-layer soil structure are very similar to the measured results.