Grounding systems under lightning surges with soil ionization for high voltage substations by using two layer capacitors (TLC) model

The grounding system behavior in the time domain for the high voltage substations is the key-parameter to ensure the system reliability during transient conditions. Many approaches are used to investigate the behavior of the grounding systems subjected to the lightning surges. These approaches aim to simplify the grounding systems by equivalent lumped circuit-parameters (RLC) or by using the electromagnetic field theory. The soil ionization phenomenon can effectively reduce the grounding electrode resistance because of changing the electrode equivalent radius located in the soils. Yet, most of these approaches have their relative assumptions with merits and demerits. The current work introduces a proposed model based on a developed grounding unit cell using the Two Layer Capacitors (TLC). The proposed cell is implemented as a unit cell to simulate the performance of the grounding system under lightning strikes with considering the soil ionization effects. Different developed models of the grounding-cells are used to simulate the behavior of the grounding system including the soil ionization process. Finite Difference Time Domain FDTD scheme is used to calculate the electromagnetic fields inside the different proposed unit cells during lightning surges. The application of the grounding unit cell is extended to be implemented for a typical high voltage substation of 500/220 kV. The grounding unit cells are presented as T neighboring sections to evaluate the overlapping between the different elementary electrodes and conductors of the complex grounding systems over the whole area of the substation. The circuit-model of the grounding unit cell is developed using EMTP-RV/MATLAB. Finally, the obtained results are compared with the similar results found in the literature with good consistency.