Transient Analysis of the Transmission Lines Terminated to Arrester Under Direct Strikes Considering the Nonlinear Phenomenon of Ionization and the Frequency Dependence Effect of Electrical Parameters of Lossy Soil

In this paper, the overvoltage of the transmission lines terminated to an arrester under direct lightning strike is computed, considering the nonlinear phenomenon of ionization and the frequency dependence effect of electrical parameters of lossy soils. To this end, electromagnetic transient solvers can be used. In this scenario, the arrester is grounded via a vertical electrode. To apply the frequency dependence of soil parameters, the approximation of equivalent frequency is used in such a way that the soil parameters are replaced with equivalent constant electrical parameters, while the nonlinear phenomenon of ionization is modelled with a nonlinear resistance in the RLC equivalent circuit of the vertical electrode. The simulation results show that the induced voltages across the arrester are different in the four scenaios (neither ionization nor frequency dependence, only ionization dependance, only frequency dependence, and both ionization and frequency dependence), specifically the induced voltage across the arrester when both effects are considered is reduced compared to the situations where both effects are ignored or only one effect is considered. This reduction for highly resistive soils and for electrodes with long lengths is more pronounced. This fact plays an important role in designing lightning arresters which should be considered by power engineers..