Frequency Dependent Grounding Impedances of Deeply-driven Ground Rods

초록

Grounding impedance depends on the frequency of current flowing into a grounding system. Especially, the lightning gives a broad frequency spectrum from low frequency up to 1 MHz. So the grounding impedance related to high frequency current like lightning should be measured with high frequency source. In this paper, we described the grounding impedances of deeply-driven ground rods of 10 ~ 48 m long with respect to the frequency of injected current and the feed point. For the experiments, we used the wideband power amplifier which can produce sinusoidal voltages with the frequency ranges of DC ~ 250 MHz. The longer the ground rod is, the lower the ground resistance is. However the grounding impedance of deeply-driven ground rod at high frequency is significantly increased. As a consequence, it is important to evaluate the high frequency performance of grounding systems for lightning protection.