Evaluation Method of Impulse Discharge Performance of Ground Electrode Based on Soil Discharge Image

When impacted by lightning current, the impulse dispersion performance of the grounding device is significantly affected by the dispersion performance of soil near the ground electrode. This effect is mainly reflected by the phenomenon of soil spark discharge. At present, engineers use the empirical formula to convert the soil spark discharge to the impulse coefficient of impulse grounding resistance. Therefore, there is no available quantitative analysis method to evaluate soil impulse dispersion performance. To solve this problem, we present an evaluation method for the impulse discharge efficiency of soil by using X-ray images, define VI as the parameter, which is the volume of discharge region to the ratio of the peak impulse. Then, the rationality and validity of the method are verified. Finally, the variation rules of impulse discharge efficiency are analyzed in different soil. Results show that the VI can reflect the impact of soil medium property on the grounding device impulse discharge efficiency more clearly, and this parameter provides a new idea for enhancing the impulse dispersion performance of soil near the ground electrode.

I. Introduction

The impulse dispersion characteristics of grounding devices are determined by soil impulse dispersion performance, ground electrode structure, and buried depth. In areas with high soil resistivity, to improve the impulse dispersion performance of tower grounding devices, the commonly used measures include changing soil, extending ground electrodes, increasing ground electrodes, and lengthening vertical ground electrodes. The above measures are mainly carried out according to the operation experience, lack of appropriate analysis means to choose. The literature has shown that soil is the key to affect the impulse dispersion performance of grounding devices [1]. Especially, spark discharge will occur when the impulse current is injected into the ground electrode, which significantly improves the impulse dispersion performance of the grounding device [2]–[3]. Therefore, the accurate evaluation of soil impulse dispersion performance can provide a basis for the selection of soil resistance reduction measures.