Analysis of the Transient Behavior of Grounding Systems with Consideration of Soil Ionization

When lightning strikes a substation or transmission tower, the high current generated by the stroke would flow into the grounding system. Ionization of the soil will occur if the current is very large and the transient behavior of the grounding system would be greatly affected. A model with lumped time-varying parameters is developed and implemented to calculate the transient behavior during lightning strokes. The conductivity of the soil affected by ionization increases considerably with respect to its value obtained with the low magnitude and low frequency, which can modify the current path. Original soil parameters can be restored to their initial values only at the end of the following de-ionization process. The effects of different parameters on the transient behavior of the grounding system subjected to lightning impulse current are analyzed.

I. Introduction

Since lightning stroke is modeled by pulses of energy with high-frequency components, grounding systems for lightning protection tend to utilize short straight conductors to reduce the self-inductance and skin effect. Experimental investigation of the effect of the impulse current on the square and rectangular earth grids was conducted in [1]–[2]. The impulse resistance was found to be higher than the power frequency impedance. The impulse impedance was defined in [3] as the ratio of the peak voltage to the peak current at the injection point.