Abstract
The most common grounding arrangements of the distribution grid and of electrical installations include vertical rods. Therefore, the accurate calculation of their ground resistance is very important for the personnel and the grid safety. For the case of vertical ground rods, no frequency-dependent analytic formula for calculating ground resistance exists. In this paper, the analytic expressions for the ground resistance of a vertical ground rod in homogeneous earth are presented. These analytic expressions are also the only ones that include the effect of the fault type, i.e. of the current frequency. Typical ground arrangements of vertical rods are examined for various earth resistivities, proving that the value of the ground resistance depends greatly on the frequency of the current, on the rod length and the earth resistivity. The results are evaluated and compared to those obtained by common formulas used until now, that do not include the frequency dependence.
Published Version
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