Evaluation of the transmission tower and frequency-dependent soil parameters influence on the grounding potential rise waveforms

In this paper, the influence of the transmission tower and the frequency-dependent soil parameters on the grounding potential rise (GPR) waveform is evaluated. This evaluation is performed using a physically consistent electromagnetic model that determines the transient behavior of the grounding system submitted by lightning, together with the Alternative Transients Program for the representation of aerial elements (tower, phase cables and shield wires). This model was developed in the frequency domain and, in this way, allows the inclusion of frequency-dependence of soil electrical parameters. In this sense, three formulations of the dependence in question are considered, widely disseminated in the literature, and determined through systematic measurement processes. The results illustrate that the concomitant inclusion of the tower and the frequency-dependence substantially modifies the GPR waveforms, when compared with those in which isolated grounding is considered, especially for soils with high resistivity values and for first return strokes. This is of most importance when evaluating personal safety criteria in the transmission tower vicinity. In these situations, the GPR waveforms should be determined by considering the presence of the tower and not only with the isolated grounding, since the transient step and touch voltages are directly associated with GPR.