Q290 : Modelling a Grounding Grid with a Known Impedance in HIFREQ
Question I need to model several large grounding grids, as part of a large network. Each grid has to have an impedance of 1 Ohm. I could explicitly model the grids in HIFREQ, but I would quickly run out of conductors. What else can I do?
Answer It is possible to simulate a grounding grid with a known impedance using a combination of GPR energization and a "lumped" impedance. Such a model does not reproduce the earth potentials and electromagnetic fields correctly in the area immediately surrounding the grid. The grid will effectively be reduced to a single point. Moreover, the current injected into this "grid" will simply disappear, and will therefore have no effect on surrounding buried structures. This approximation should therefore be used only to model a "distant" grounding grid which is expected to have no effect on the potential and electromagnetic fields near the structures of interest.
The approach consists in using two conductors, the first one energized with a GPR energization at 0 Volt, to simulate a remote ground, and the second one containing carrying a lumped impedance with the desired value. As usual for a GPR energization, the origin node of first conductor should be floating. Then, one end of the conductor carrying the impedance (as specified using its CONDUCTOR-TYPE) should be connected to the end node of the first segment, and the other should be connected to the network.
Note that it isn't necessary that these two conductors be buried; they can very well be located above ground.