TRANSIENT PERFORMANCE OF SUBSTATION STRUCTURES AND ASSOCIATED GROUNDING SYSTEMS

When lightning strikes an electric substation, large currents generate d by the stroke Bow in the above ground structures and grounding syste m and dissipate in the soil. The electromagnetic fields generated by s uch high currents may cause damage to equipment and may be dangerous t o personnel working nearby. In this paper, the frequency and time doma in performance of a substation subjected to a lightning strike is desc ribed 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 cas es are considered. The first case examines the substation grounding sy stem only, while the second case includes an above-ground structure as well. It is believed that the results of the second case have not bee n published before. A double exponential lightning surge current is in jected 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 soft ware package. The temporal and spatial distributions of the electromag netic 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 in to account. The analysis sheds some new light on the understanding of the effects which take place at the higher frequencies.