Transient analysis of earthing electrodes considering soil ionization phenomenon under lightning impulse condition

Abstract

This paper presents the transient behavior of an earthing system under the influence of lightning current injected in to it. Vertical rod and horizontal electrode buried in homogeneous soil are considered in this analysis. Statespace representation based transmission line methodology is adopted with non-linear parameters for modelling the earthing electrodes in the time domain. Soil ionization phenomenon is taken up with the presence of residual resistivity. In this method, soil resistivity variation is adopted to evaluate the soil ionization phenomenon that occurs due to changes in the electric field. This study incorporates mutual coupling between the electrode segments for low and high soil resistivity. Earthing electrodes are subjected to a high-magnitude of lightning current impulse with different peaks. Transient voltage and impulse impedance are calculated to analyse the transient behaviour of earthing electrodes with soil ionization. Impulse impedance of vertical earthing rods and horizontal electrodes are calculated and compared with the power frequency impedance. Percentage ohmic reduction between them is also reported. The influences of critical electric field, soil resistivity and lightning magnitude on transient performance of earthing electrodes are calculated. Also, an effect of the front time of lightning current impulse for a fixed peak on the impedance of the earthing electrode is evaluated and a significant amount of changes are observed. Simulated results are validated with the experimental and theoretical results reported in the literature, and good agreements are found.