Análise teórico-experimental da ionização do solo submetido a campo elétrico de alta intensidade e não uniforme gerado por correntes impulsivas

Abstract

This thesis presents the results obtained from the analysis of a large database of impulsive current tests applied to fifteen soil samples arranged in a coaxial cylindrical vat, representing an electric field scenario with a non-uniform characteristic. Each sample was tested at three different moistures (natural, 5% moisture and 10% moisture) and the tests were performed for two wavefront times (fast front, referring to impulsive currents with characteristics of subsequent return strokes and slow front, concerning with the first strokes). Although soil ionization has already been widely investigated, the construction of such an extensive database for the analysis of the dynamics of the effect evolution, contemplating the effects of resistivity, moisture and wavefront time, is pioneer. Altogether, more than 7,300 tests were validated with recording of impulse voltage and current waves obtained from a 600kV impulse generator. A computational routine was created to process the database and carry out the proposed analyses. It was observed that variables such as moisture, wavefront time and resistivity don't significantly influence the evolution of the ionization process, with the intensity of the electric field being the determining parameter for the occurrence of the phenomenon. For the considering the soil ionization effect, the work suggested using a curve relating the linear density of current dispersed from the electrode to the soil with an increased equivalent radius of the electrode. This curve was obtained considering the decrease of the transient impedance of samples as a function the electric field strength at the electrode surface. Attributing a conservativeness degree to this curve (e.g., decreasing the linear current density in about 10%, corresponding to an increase of the same order of the electric field intensity), allows using it for taking the ionization effect of generic soils around cylindrical conductors into account.