Comments on the high-frequency response of hemispherical grounding electrodes with emphasis on magnetic induction effects

• Published in: Electric power systems research Vol. 238; p. 111100
• Main Authors: Brandão Faria, José, Machado, Vitor Maló
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2025
• Subjects: Electrode inductance; Electromagnetic modeling; Grounding impedance; Hemispherical electrode; High frequency; Magnetic field effects; Electromagnetic modeling; Magnetic field effects; Electrode inductance; Hemispherical electrode; Grounding impedance; High frequency
• ISSN: 0378-7796
• DOI: 10.1016/j.epsr.2024.111100

•Inductance of hemispherical grounding electrodes.•Electrode impedance based on an electromagnetic field approach.•Analytical solutions for low and high frequencies.•3D benchmark for numerical solvers. Accurate calculation of electrodes’ impedance is of major importance for the operation and protection of overhead power lines whose towers are periodically bonded to earth via grounding electrodes; particularly when the towers are hit by lightning discharges. A recent paper has proposed a simple RC-circuit to model the frequency response of hemispherical electrodes which predicts a continuous decrease to zero in electrode impedance as the frequency increases. The prediction agrees with the model, but the model is not sound and, therefore, the prediction is disputable. We show that the model is inadequate because it is founded on the conviction that the magnetic field is zero everywhere inside the soil ___which we claim is a mistake. We employ a full-wave FEM solver to recalculate the numerical results presented in that paper and observed a notable disagreement for high frequencies. In addition, we also show how the problem of calculating the impedance of hemispherical grounding systems can be solved, encompassing displacement-current effects and magnetic-field effects.