Analysis of Transient Performance of Grounding System Considering Soil Ionization by Time Domain Method

The grounding system is very important for lightning protection. If the lightning current is large enough, soil will be ionized, which will have a great effect on the transient performance of the grounding system. In this paper, an efficient time domain method is proposed to analyze the transient performance of the grounding system. The method takes account of nonlinear soil ionization, the shielding effect among electrodes, and frequency-dependent parameters all together. First, a frequency domain circuit model is set up based on a moment method coupling with circuit theory. Then, the model is approximated by a frequency-independent circuit model with the help of vector fitting method. Finally, the time-varying soil ionization is considered by making corresponding parameters time-varying when a time domain method is used to solve the circuit model. The method is validated by field test.