A simplified method for calculating the impulse resistance of vertical grounding rods

A simplified method is proposed for calculating the impulse resistance of vertical grounding rods. The analytic formula is first derived to determine the low current resistance and then the calculation procedure is developed to estimate the impulse resistance. In the procedure a nonlinear relationship is introduced to characterize the electric field and current density in the ionization zone surrounding the grounding rod. The effective radius of the grounding rod is evaluated according to the nonlinear relationship. The impulse resistance is calculated by substituting the effective radius into the analytic formula of the low current resistance. Finally, a comparison is made between calculated and measured results in confirmation of the validity of the proposed method.