Impedance with respect to vertical and rotational symmetric grounding electrodes and its computational results from full-wave analysis using FD-TD method

To ensure the electromagnetic compatibility (EMC) of sensitive electronics, such as information devices in private houses and controllers including digital relays in substations, it is important to study the transient performance of grounding systems for lightning surges. In spite of vertical grounding electrodes being widely used in private houses and substations and being very familiar as grounding systems, their frequency response, such as impedance, is not yet clear. If we can elucidate their frequency response, we can incorporate them, for example, into the Electromagnetic Transient Program (EMTP) and can ensure better EMC than that presently available. In this paper, for the vertical and rotational symmetric grounding electrode, we described the impedance to be the complex ratio of the potential at top of the electrode to the current flowing into it in the frequency domain. As an example, while changing the conductivity of the ground, we calculated the impedance of an electrode 10 mm in diameter and 3 m in length buried in the ground using the full-wave computational method for analysis of the transient performance of grounding systems based on the FD-TD (finite-difference time-domain) method and the Fourier transform.