A study of influencing factors about vertical grounding rods performance in two-layer soil

In high resistivity soil and small grounding grid acreage, grounding resistance of power plant and substations may not meet the relative national regulation just by using horizontal grounding grid, so the resistance reducing measures should be adopted. The influences of the reflective coefficient of the double-layer soil, the top-layer soil thickness and the length of vertical grounding rods on the resistance-reducing ratio were analyzed by the CDEGS software package. The results show that if the reflective coefficient is identical, the difference of the top- layer soil resistivity has little effect on the resistance-reducing ratio. The resistance-reducing ratio decreases as the reflective coefficient increases. If the length of vertical rods is less than the top-layer soil thickness, the reflective coefficient influences the resistance-reducing ratio feebly. The resistance-reducing ratio increases with the increase of the length of vertical rods and gradually reaches saturation state. If the reflective coefficient is negative, the vertical grounding rods which are long enough to reach the bottom-layer soil can effectively decrease grounding resistance.