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. |
