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Direct Time Domain Analysis of a Grounding Electrode Based on the Antenna Theory

The grounding electrodes play important role in protection of telecommunication systems and electrical power systems against overvoltages and fault currents. Thus, the analysis of the transient behavior of grounding electrodes is necessary for an efficient design of the protection system. In general, the transient response of any linear system could be obtained directly, by solving the time domain equations, or by frequency domain approach and inverse Fourier transform. Previously used models can be classified as circuit approach, transmission-line approach and antenna theory approach. Antenna theory approach is most accurate one, but also the most demanding and, until now, limited to the frequency domain analysis. In this work a novel time domain model of the grounding electrode based on the wire antenna theory is proposed. Grounding electrode is modelled as a thin wire antenna excited with the current source at the wire end. The formulation is based on the correspondig homogeneus time domain Pocklington integrodifferential equation for thin wire in infinite lossy medium. Rather demanding Green function containing convolution and the Bessel function is simplified assuming the low conductivity of the soil. Thus obtained equation is numerically handled via the time domain Galerkin-Bubnov scheme of the Indirect Boundary Element Method (GB-IBEM). Current distribution along the wire for each time step is obtained using the adequate marching on in time procedure. Validity of the proposed model is tested using antenna theory approach in frequency domain and inverse Fourier transform.

Grounding electrodes; direct time domain analysis; thin wire antenna; GB-IBEM

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