Independant earth electrodes

[baltoche]

Dear electician friends,

 

Suppose I have got two horizontal ground grids laid at the same depth and separated by a distance "d". How to calculate "d" so that my grids are independant from each other, meaning that I can bond them together and calculate an equivalent resistance by 1/(1/R1+1/R2) ?

 

With my thanks !

[Enthalpy]

Hi again,

 

there are still many ways to understand you description... I suppose at least that a grid consists of many wires in the ground.

 

If the resistance of one grid results mainly from spreading the current near the wires, then you need only the other grid to be a few wire diameters away. That is, you could just as well have a single grid with twice as many wires and obtain half the reistance - logically enough for this case.

 

If you have enough wires that the resulting resistance resembles one big solid electrode occupying the same ground area, then the second grid must be a few area diameters away from the first one.

[baltoche]

I indeed assumed that a grid consisted of a loop (with intermediate crossbonds) of round copper or steel buried in the ground and occupying a given surface (Lxl). During an MV fault, part of the fault current will be dissipated in the ground through this grid (called A). At the same time, another part of the fault current will dissipate in the same ground through another nearby grid (called B). I guess that my influence zone related to grid A depends on the fault current dissipated through A besides the geometry of the grid itself. Same case for grid B.

Is there a way to assess the respective influence zones of grids A and B from a geographical point of view so as to assess the overlap between them ?

 

Thanks and Regards.

[Enthalpy]

Suppose that you bury enough wire length, so the mesh behaves nearly as a solid sheet, which you model as a radius=R hemisphere only because it's manageable. Choose R for 2piR² = L*l for instance.

 

For some current injected by electrode A raising a voltage V there, you get a voltage V/n at the electrode B distance from A by n*R, so choose n.