How to add bentonite into IEEE 80
How to add bentonite into IEEE 80
(OP)
I am designing an earthing grid in a soil with very poor resistivity (~3000 ohm.m), (calculation returns a resistance of 12 ohm) the resistance required shall be <0.5 ohm which seems impossible, I think we will need to use Bentonite but don't know how to calculate the required quantity to achieve such reduction?
any ideas?
any ideas?






RE: How to add bentonite into IEEE 80
You can add something to the soild, however, you should have in mind the following:
1) Despite adding something to the soil, this will be temporal. I mean, in some time the effect of the added material will have passed and the earth resistance will be againg very high.
2) I understand your soil resistance is extremely high, however, is that the value independently of the deepth?
What I would think is about teh possibility to go deeper in order to find a lower resistance lawyer that allows you a better value.
3) The other point could be:
What are the touch voltages calculated using the 12 Ohms?
Do they keep you on the safe side or not?
I think that the target value (0.5 Ohms) is because of the sensitive equipment, so what I recommend you is to look to extend the grounding grid using as much area as possible because in that way the whole resistance value tends to be reduce.
Also take a look at Ufer Grounding systems, the explanation could be usefull to you
Regards
RE: How to add bentonite into IEEE 80
However, to improve the earth resistance, the better method is to go for the deep-well electrodes. This is a permanent solution. We have been using this in the deserts, where the soil resistivity was 3400Ω-m.
RE: How to add bentonite into IEEE 80
Since the station is connected by UG cables with sheaths connected to ground at remote ends, I am sure that the ground return fault current won't exceed few hundred Amperes and the total resistance will be very small (about 10 remote ends, all connected in parallel), would this be acceptable? what about sensitive equipment?
the touch voltage with 12 ohm went crazy exceeding 450 kV!!
RE: How to add bentonite into IEEE 80
RE: How to add bentonite into IEEE 80
Is your facility based on NEC code?
If it is, then, what short-circuit current are you taking into account for your calculations?
The one in low voltage or the one in medium?
This could be easier if you have a very clear picture of your grounding system and real needs
RE: How to add bentonite into IEEE 80
We should know what is the system voltage you are talking about and what is the maximum earth fault current. Also please note that if it is an earth mesh, the value looks to be ridicules.
My experience is that for the switchyards or substation having earth mesh, the touch potential and step potentials are not a big issue. By increasing the quantity of grid earthing conductor you can bring it down to the acceptable value. The main problem is with the "Ground Potential Rise GPR)"
SO in my opinion you have to change the way you look at the problem.
RE: How to add bentonite into IEEE 80
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Please note that the deep well earthing station need not be in the same substation. It can be made in a relatively friendly terrain. Then you should connect the deep well earth station to the new substation ground grid with adequately sized earthig conductor. Sorry, that I am not using the precise terminologies from NEC, as I am now not using the NEC!!!
RE: How to add bentonite into IEEE 80
With respect to corrosion, concrete is sometimes used to encase a grounding rod to prevent deterioration of your ground due to corrosion. Maybe, you can use the piles for grounding if you choose the right concrete.
RE: How to add bentonite into IEEE 80
increase the value of the touch voltage by add surface material like washed granite similar to pea gravel,
to take in account the split factor in order to reduce the value of the current in the ground resistor who will allow you to decrease GPR.
RE: How to add bentonite into IEEE 80