Investigação da resposta de malhas de aterramentos frente a correntes de descargas atmosféricas

Abstract

The response of grounding grids subjected to lightning currents wasassessed following two different approaches: experimental tests andcomputational simulations. The experimental tests comprise the impression of currents on the electrodes in different positions of two grounding grids, buried in high- and low-resistivity soils. Currents waveforms with typical time parameters of first and subsequent strokes were used during the experiments. Moreover, currents presenting very short front times (about 150 ns) were used in order to stress the propagation effects in the soil. All the difficulties inherent to this kind ofmeasurement were overcome, allowing achieving outstanding results,consisting basically of GPRs (Grounding Potential Rises) and corresponding currents impressed in different positions in the grid. Soil ionization was not analyzed and, therefore, currents of low amplitude (few amperes) were used. The variation of soil resistivity and permittivity along the frequency range of lightning-current components was determined and its effects on the response of the grounding grids were included in the simulations. The experimental and simulated results show excellent agreement when the effects of the frequency dependence of soil parameters are considered in the simulations, especially under conditions of grounding grids buried in high resistivity soils, where these effects are more pronounced.