Transient impedance of the vertical grounding electrode

Abstract

The paper deals with the calculation of the transient impedance of a vertical grounding electrode. The mathematical model is based on the thin wire antenna theory. The formulation of the problem is posed in the frequency domain while the electrode transient response is obtained by means of the inverse Fourier transform. The current distribution induced along the vertical conductor due to an injected current is obtained by solving the frequency domain Pocklington integro-differential equation via the Galerkin Bubnov Boundary Element Method (GB-BEM). The presence of an imperfectly conducting half-space is taken into account via the reflection coefficient. Expressing the electric field in terms of current distribution along the electrode the feed point voltage is obtained by integrating the normal field component from the electrode surface to infinity. The frequency dependent input impedance is determined by a ratio of feed-point voltage and the value of the injected lightning current. The frequency response of the grounding electrode is obtained multiplying the input impedance spectrum with Fourier transform of the injected current waveform. Finally, the transient impedance of the vertical electrode is calculated by applying the inverse Fourier transform to the frequerncy response spectrum.

Ranko Goić

Full Professor | Department of Power Grids and Substations

Full professor at the Faculty of Electrical Engineering, Mechanical Engineering, and Naval Architecture in Split exeperienced in transmission and distribution networks, renewable energy sources (RES), power system planing and economics