Transient performance of substation grounding systems subjected to lightning and similar surge currents

The frequency and time domain performance of a typical substation grounding system subjected to a lightning strike is described and discussed. The computed scalar potentials, electric fields and magnetic fields are presented graphically as a function of spatial coordinate, as a function of time and as a function of both. First, a double exponential lightning surge current is injected into the center of a square ground grid. This same surge current is then injected at one corner of the grid. The response of the grounding system to the frequency domain electromagnetic spectrum of this signal is computed by a frequency domain electromagnetic field analysis software package. Once all the frequency responses have been computed, the temporal and spatial distributions of the electromagnetic fields inside and near the substation are obtained by an inverse Fourier transformation of all these responses. The results are compared with some well known low frequency results and to published work in this area. These results indicate that the performance of the grounding system is significantly dependent on frequency and on the point of impact of the lightning strike