Impulse Characteristics of Tower Grounding Devices Considering Soil Ionization by the Time-Domain Difference Method

Knowledge of impulse characteristics of tower grounding devices is important for lightning protection of the transmission lines. In this paper, the time-domain difference method is proposed to analyze the impulse characteristics of tower grounding devices. Combined with the soil ionization model and the soil-critical breakdown field strength, the proposed method is capable of modeling nonlinear ionization of the soil. The voltage-response waveform calculated by the proposed method is smooth, which is superior to the waveform calculated by the frequency-domain numerical algorithm. The reduced-scale experiments of grounding devices with different structures were carried out in the laboratory to validate the accuracy of the proposed method. Furthermore, the critical breakdown field strength used in the soil ionization model is measured by the coaxial cylindrical electrodes.