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Arctic Grounding Systems

Arctic Grounding Systems

Arctic Grounding Systems

(OP)
I'm actually designing a grounding systems for arctic climate.
This thread is a follow up of an older thread thread238-196015: Grounding Resistance in Arctic as to be a sample application.

1.0 Definition

Artic : Regions where the soil is compose of permafrost. It includes Alaska, Northern Canada, Northen Scandinavia, Northern Russia and Antarctica

2.0 Reference
Will be mentionned is this thread consideration from
[1]Nationnal Electrical Code (NEC) - NFPA 70
[2] Canadian Electrical Code (CEC) - CSA C22.1
[3] IEEE Green Book - IEEE Std 142-1991
[4]ROY T. BECK and Luke YU Design Consideration for Arctic Grounding Systems - IEEE Transactions on Industry Applications, Vol. 24, NO. 6 November/December 1988
[5]IEEE std 80-2000

3.0 Project details
Water treatment plant. The building consist of one module on steel pillings. The space between the pillings will be filled by 3/4 crushed rock over the permafrost soil.

4.0 Comparisson between thread238-196015: Grounding Resistance in Arctic and local standards.
The main recommandation from the mentionned thread is to leave installation ungrounded since the soil is too resistive. Being in Canada, the CEC requires safe grounding. The CEC use limits of GPR, touch and step voltage (for ground bed).

5.0 Reference [4]
This article gives hints about designing artic grounding system. I could find there typical permafrost resistivity range. There was also a discussion about Earth Electrodes. The summary is that earth electrodes aren't sufficient to provide a low ground resistance (test exemple resistivity results to near 400 ohm). Ground mats are quite expensive for not that good results. But that using pillings as ground electrodes shown favorable results. Cause the pilling have larger diameters than typical electrodes and buried deeper (ours would be 10 meters underground) The article points that measurements showed 15 ohm for one pilling.

I recommended this paper

6.0 Grounding Philosophy.
We are grounding the building through the pilling. To verify are hypothesis, I estimated the "mats" resitivity with soil. Mats consist of a conductor on the building (62m x 24m) perimeter connected to a range number of pilling. I used formula from [5].
Results goes from Rg = 34 ohm to 50 ohm. From 45 pillings to 4 pillings (corners). I found that if I'd compute a graph Pillings/ohm it would give a inversely exponential curve. 22 pillings gives 36 ohms. 80 pillings gives 34 ohms. So 34 ohm is the best I could get.

Note that this conductor is connected to the common neutral of the whole complexe (lots of module).

7.0 About the network grounding
The main bus at the power house is low impedance grounded at through a zig zag transformer. The power station grounding inside the water treatment plant (the electrical room) is still to be determined. But transformer throughtout the complex are high-impedance grounded.

8.0 About the futur
The design is based on a lot of documented assumptions and I will keep a close look on this grounding application, especially since it's the very first time I commit myself on grounding.   

Danny Garant, ing.jr
Groupe Stavibel Inc.
www.stavibel.qc.ca
 

RE: Arctic Grounding Systems

Use of pilings for ground in the western & eastern arctic is very common, with reasonable results.  A lot depends on local conditions.  You could also look at what is going to go into the bore hole that the pilings are going into.  Different compounds are dumped in these, and I've often wondered if instead of the typical cement, a conductive cement would be acceptable to the structural designer.

Also, have a talk with the local AHJ, as they often have the best information on the local site conditions.

RE: Arctic Grounding Systems

(OP)
A ground rod provider suggest a fill to enhanced conductivity between rods and soil.
Though, the provider didn't know about the arctic condition of the project.
But it might be more than just structural design consideration but also an environnemental consideration since environmentale requirement about arctic soil are there to protect the permafrost intergrity. Pillings are not as damaging as cement foundation, so it's one of the reason why they are so popular. Also, since the pillings are long enough to be stuck on the always frozen layer of soil, there is negligable vertical structural working, however horizontal working are possible.

Can I have the whole words for AHJ. I don't understand what this acronyme is for.

Thanks
 

Danny Garant, ing.jr
Groupe Stavibel Inc.
www.stavibel.qc.ca
 

RE: Arctic Grounding Systems

AHJ: authority having jurisdiction.  It will be the local inspector.  I assume, because you are using the CEC, this will be in Canada, and most arctic communities are tiny, I would not recommend talking to the local inspector, but to the whomever they report to.

You might also want to talk to the local utility company to see what they do in the region.

I know these are not helpful for you to calculate the ground resistance, but talking to these folks will help you design something that hopefully has a proven track record.

RE: Arctic Grounding Systems

(OP)
Thanks for the acronym.

The project is for a mining complex. They act as community, utility and previous module design served as pre-approved philosphy that we adapted to this projet. Past history shows no use of filler to improved conductivity for their current installation.

I would ask about filler adapted to artic conditions. Since we think that cold conditions could cause the filler to lose it's properties.

Danny Garant, ing.jr
Groupe Stavibel Inc.
www.stavibel.qc.ca
 

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