A Discussion on Practical Limits for Segmentation Procedures of Tower-Footing Grounding Modeling for Lightning Responses

摘要

In this article, we evaluate the practical limits of length segmentation of tower-footing grounding modeling. The objective is to present a relation between computational efficiency and segmentation for transmission lines lightning performance studies. A physically consistent electromagnetic model based on field theory is applied. The segmentation process is designed to improve computational efficiency, in relation to the proposals suggested in the literature, and to maintain the precision of the results. The criteria considered acceptable for a given segmentation (in relation to a reference) are as follows: 1) the grounding potential rise (GPR) must have a peak value up to a maximum of 10% higher, 2) the lightning overvoltages peaks on the tower top (and insulator strings) must have a peak value up to a maximum of 5% higher, and 3) the GPR waveforms shall follow the same pattern (the same being valid for overvoltages). Soils with low (50–300 $Omega {cdot}$ m), medium (300–1000 $Omega {cdot}$ m), and high (1000–4000 $Omega {cdot}$ m) resistivities are considered. The relative permittivity is maintained at 10. The results illustrate that the optimum segmentation can be as great as 1000 times the radius of the electrode. This ratio is higher than the maximum segment sizes suggested by the technical literature. The computational gains are quite high (over 30 times faster).