How to reduce earthing resistance in a rocky area 1

[victa1288]

We did some testing on the ground rod system in one of our stations. The test results are extremely high. It was 1800 ou with one rod. It was 200 ou with 8 rods and bullding steel structure. I think it is due to a poor design.

We are thinking of reducing the soil resistivity by injecting some chemical products. But I don't know which manufacturers make this kind of products in Canada, or in USA. Could you please direct me to the right manufacturers?

Thank you in advance.

 

[dpc]

http://www.erico.com/products/GEM.asp

 

[alehman]

http://www.lyncole.com/p.lynconite.asp

 

[victa1288]

Thanks for the hints.

What happened was, the pin resistivity the soil company measured is 71,000 ou-cm, which is 710 ou-m. Engineering company did the designbased on this. Actually, the soil resistivity for the dry gravel is high up to 100000 ou-m.
That's why the grouding resistance is too high.

 

[SilverArc]

Hi,
I just thought of sneaking my question as it is related .
In the link below in fig. 1, Could you kindly advise me that why the author is showing the potential plot below the grid in a two half semi circles. I mean, how can we be sure that beneath the earth the potential will have this shape.

http://www.era.co.uk/Docs/ECS/Ground_ROD_Tutorial.pdf#search="touch voltage step potential + grid"

Last point, if you notice in fig. 1., If I understood correctly, remote earth refers to the grouding of a conductor housed in the substation where the grid is in reference to where the other object is grounded. An example could be probably a communication equipment that is used in a substation where the grid in question is but grounded some where else.

Please advise, what I am missing here.
Regards,

 

[jghrist]

The potential shown by the dashed lines is not the potential beneath the earth. This is the surface potential as it varies along a line on the surface and it is shown below the surface for convenience. The potential plot is not semicircular. The shape depends on the flow of current through the soil from the point of the fault (the substation grid) to the source of the current. The surface voltage is highest directly above the grid wire, as indicated by the peaks at the grid wire locations. Outside the last grid wire, the surface potential decreases (at a decreasing rate) until it reaches zero at remote earth.

Remote earth refers to the point where the fault current returns. The man at the right is standing far enough away from the station that the surface potential has decreased to close to zero. He is touching a piece of steel that is connected to the grid wire, so is at the grid potential. The steel "transfers" the potential of the grid to a remote location. The Ground Potential Rise (GPR) is the potential of the grid during a fault with respect to remote earth. Another example of transferred potential is the communication equipment you mention that is grounded to a communication cable shield that is grounded not at the station, but at a remote location. In this case, the zero potential of the remote location is transferred to the high potential area of the local substation.