抄録
It is needed to study the transient performance of grounding systems for lightning surges to ensure the electromagnetic compatibility (EMC) of sensitive electronics such as information devices and digital relays in substations and/or residential houses. Therefore, an easy method of estimating frequency response to represent the transient performance of grounding systems and its incorporation into Electromagnetic Transient Program (EMTP) are highly desired.
EMTP based on circuit theory has been applied to resolve the transient performance of electrical apparatus consisting of cables and conductors which are parallel to the ground surface, in which the propagation of TEM waves that are plane waves is implicated, and devices such as surge arresters represented by lumped elements. However, conductors which are vertical to the ground surface have not been modeled because TM waves propagate on such conductors and the characteristics in early time, when the approximation of plane waves is not adapted, are required.
In this paper, for the vertical and rotatory symmetric grounding electrodes, we propose a computational method for the impedance, which is defined as the complex ratio of the potential of its top at the ground surface to the current flowing into it in the frequency domain. The potential is derived from the integral of the horizontal component of electric fields along the path reaching the electrode on the ground surface because the potential could be uniquely defined in the case of a horizontal plane by considering the electromagnetic field in the configuration discussed here.
We then calculated the potential of the electrode and current flowing into it in the time domain by computational analysis of transient performance based on the FD-TD method (CATP) and the impedance up to 20MHz in the frequency domain were derived using the Fourier transforms of the potential and current in the time domain.
