CDEGS
CDEGS
(OP)
Guys,
I have 26 KA ground fault to be taken care by ground grid. I have put so much copper and rods but it doesn't change that much. Should I put ground well or anything else?
Any help would be appreciated,
I have 26 KA ground fault to be taken care by ground grid. I have put so much copper and rods but it doesn't change that much. Should I put ground well or anything else?
Any help would be appreciated,






RE: CDEGS
Usually, major touch voltages appear around corners and outer regions (fringe effect)
RE: CDEGS
May be I should put more rods around those areas.
RE: CDEGS
RE: CDEGS
RE: CDEGS
You could also model pier foundations as grounding electrodes (UFER) if you provide a means to connect the rebar to the ground grid. Perhaps clipping the rebar to anchor bolts which connect to grounded steel structures. I agree with HamburgerHelper that you need to model reinforced concrete slab foundations. They will be almost equipotential surfaces without high touch-voltages. The area covered by concrete slabs could be ignored instead of modeled; it won't have the highest touch-voltage.
RE: CDEGS
RE: CDEGS
RE: CDEGS
If concrete has same resistivity as top soil layer, why we even model it?
RE: CDEGS
That's why I said
RE: CDEGS
Some specs ask for epoxy coated reinforcement bars, making the model almost useless as the bars will have virtually no contact with soil when bonded to the main grid.
what about soil replacement?
Did you check the actual earth return current? you need to run a fault distribution study on CDEGS and fault contribution study (ETAP/DigSilent) to get the actual grid return current going to grid through neutrals for remote (out of substation) faults. This may not be easy but can help reduce the design current greatly.
RE: CDEGS
https://en.wikipedia.org/wiki/Ufer_ground
Excerpt:
During World War II, the U.S. Army required a grounding system for bomb storage vaults near Tucson and Flagstaff, Arizona. Conventional grounding systems did not work well in this location since the desert terrain had no water table and very little rainfall. The extremely dry soil conditions would have required hundreds of feet of copper rods to be inserted into the ground in order to create a low enough impedance ground to protect the buildings from lightning strikes.
In 1942, Herbert G. Ufer was a consultant working for the U.S. Army. Ufer was given the task of finding a lower cost and more practical alternative to traditional copper rod grounds for these dry locations. Ufer discovered that concrete had better conductivity than most types of soil. Ufer then developed a grounding scheme based on encasing the grounding conductors in concrete. This method proved to be very effective, and was implemented throughout the Arizona test site.
Bill
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"Why not the best?"
Jimmy Carter
RE: CDEGS
RE: CDEGS
The concrete foundations reinforcement bars are generally connected to the grounding grid and may improve the grounding performance of the grid. The concrete itself, being a very hygroscopic material, tends to attract moisture from the neighboring soil and will eventually acquire to same resistivity as the soil it is in contact with. Consequently, you often can model the rebar only, and omit the concrete volumes.
Ufer grounds from Wikipedia
Concrete is naturally basic (has high pH). Ufer observed this meant that it had a ready supply of ions and so provides a better electrical ground than almost any type of soil. Ufer also found that the soil around the concrete became "doped", and its subsequent rise in pH caused the overall impedance of the soil itself to be reduced.[3] The concrete enclosure also increases the surface area of the connection between the grounding conductor and the surrounding soil, which also helps to reduce the overall impedance of the connection.
For what it's worth.
Bill
--------------------
"Why not the best?"
Jimmy Carter