Transient performance of substation structures and associated grounding systems

When lightning strikes an electric substation, large currents generated by the stroke flow in the aboveground structures and grounding system and dissipate in the soil. The electromagnetic fields generated by such high currents may cause damage to equipment and may be dangerous to personnel working nearby. In this paper, the frequency and time domain performance of a substation 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 coordinates, as a function of time and as a function of both. Two cases are considered. The first case examines the substation grounding system only, while the second case includes an aboveground structure as well. It is believed that the results of the second case have not been published before. A double exponential lightning surge current is injected at one corner of the substation. 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. 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 presence of a soil with an arbitrary resistivity and permittivity is accurately taken account. Analysis sheds some new light on understanding of the effects which take place at the higher frequencies