Grounding Resistance in Arctic

[pqsl]

Hi,
I am looking for guidelines / information or any help related to ground resistance measurements and also ground resistivity measurements. Looks like this topic was not discussed in this forum. Any experts on this topic?

 

[itsmoked]

Grounding is a frequent topic here. Have you done a search?

Though I would agree, "In the Arctic", isn't covered on a regular basis.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[pqsl]

Yes it is measurements in "Arctic" not covered in tsis forum.

 

[Skogsgurra]

The Arctic. That would be ice and sea water.

There is a lot of things going on in the Antarctic. Ice there too. Less water, though. Study the BAS (British Antarctic Survey) page to see if they have anything to say. I may have a contact there if you need to talk to someone in person.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[sslobodan]

If it is an ice you cant consider grounding because it should be an isolator unless you dig up hole and put probe in sea (salt water conducts electricity) and if it is frost ground like on south pole you are talking about you need ground conductivity so you can put it in standard formula. Though I would go on ungrounded system on such places due to a lot of problems you might get trying to stay in regulatory limits that apply grounding (they don't change on antarctic if in GB is lets say 4ohm allowed for the operation you need grounding for). If you are trying to find how to apply grounding than you might consider to take vessel of an object that is from metallic plates on such places (Due to a need of fast building) and connect them in a equipotential surface and connect grounding of all your gear to it. It can be done because you create electrical power on same place you are using it so you can equalize potential of neutral (referent point) but watch out pretty good because if you have difference in potential between that point and ice you will have voltage and that means someone might get killed. That is why I told you forget the grounding on such place and go with ungrounded with ground to phase short circuit monitoring. If you clear the fault when one phase hits one equipotential surface you will have no problem, system will work, two or tree creates short circuit.

 

[pqsl]

Thanks sslobodan.

My concern is grounding of land based systems north of arctic circle.
1 - Do standard methods of ground resistance measurements apply on existing installations?

2 - What is the procedure to measure ground resistivity in order to use it in ground grid design calculations?

My undersdanding is that frozen earth is at least 20 time less conductive than poor soil and frozen layer of soil would vary from one geographical are to another. So I imagine this to would cause problems to conduct soil conductivity and earth resistance measurements.

 

[sslobodan]

Found the:

http://gsa.confex.com/gsa/2002NE/finalprogram/abstract_30723.htm

They say in that abstract:
"An electrical resistivity survey conducted by the Wenner method at closely spaced electrode spacings was used to determine the vertical extent and resistivity of the frozen ground. This survey was effective in determining the thickness of 3 feet for the frozen ground and a resistivity of 1000 ohm-meters. Beneath the frozen ground the resistivity decreased to 40 ohm meters."

As you can see there can not be a word about grounding with such soil resistivity. And that was measured in New York, not on pole where you have perma frost. I was over arctic circle for 3 months in Siberia. There is no such thing as ground there. I mean you have surface that is earth, but 2m below is perma Ice and nothing melted down for god knows how long (Siberia was green valley in a time of mamuts) . Winter is 9 months in year and they can not have cultive plants, Trees with shallow roots, grass. Situation is a bit better in woods because you have something like vegetation accumulating for some time so the soil resistivity can go under those data for New York.
Problem is in general water on arctic you have almost pure water, no mineral salts in ice, and they are the one that are conducting electricity, and all the gruound is saturated with such ice. So resistivity per meter goes maybe 2 - 10 times more than that data for New York. You don't have that down limit of 40ohm, because everything is perma ice.


And here is an abstract I found of one research work considdering this subject I think you will get all you need from it:

"comparative study of the results of vertical electrical soundings (VES) and magnetotelluric soundings (MTS) carried out at Seymour and James Ross Islands (NE of Antarctic Peninsula) is conducted. Frozen ground thickness, estimated by VES, is compared with permafrost thickness estimates, obtained using: (a) steady geothermal heat flow, inferred from the depths of conductive layers in the crust and upper mantle estimated by MTS, and (b) mean annual air temperatures (MAAT). At Seymour Island, 250 m of permafrost thickness, in equilibrium with an inferred heat flow of 72 mW/m2 (corresponding to a geothermal gradient of 0.037 °C/m) and with an MAAT of ?9.4 °C, is estimated for the upper terrace (about 200 m a.s.l.). This value is consistent with the frozen ground thickness (200 m in the upper terrace) previously estimated by VES. Magnetotelluric soundings carried out in the northwestern region of James Ross Island (volcanic island with recent activity) suggest a magma chamber with top at about 7 km depth in the crust. From the depth of this conductive body, a heat flow of 145 mW/m2 and a geothermal gradient of 0.074 °C/m are estimated, suggesting 67 m of permafrost thickness in the upper terraces (35 m a.s.l.) of this island in equilibrium with the estimated steady heat flow and an MAAT=?5°C. The frozen ground thickness estimated by VES lies between 40 and 45 m for the same terrace. The differences between frozen ground thickness and permafrost thickness in both islands could be attributed to a cryopeg, according to the high salinity beneath the frozen ground suggested by MT soundings....


As you can see if you download

http://www.dranetz-bmi.com/pdf/groundtesting.pdf

You can expect the sand/loam over there (no biomass to create better ground) with around 500 000 ohm-cm resistivity which is some 200 times more than general ground and that is on normal temperature and x10 times on temperature you will measure it so you should count on 2 000 multiply factor to an normal grounding that you would calculate in bad soil next to your doorstep. I believe you know now why I told you that grounding system is impossible in such conditions...

Anyway in that file above you have some methods for measuring ground resistivity but I am not certain will you get any data because currents are to low to be measured....
You would need a gear that puts a lightning in ground to get accurate data.

 

[sslobodan]

http://www.smg.uni-karlsruhe.de/~stefan/Pubs/2005-ISEMA/P08_Hauck.pdf

Describes methods for doing that ground resistivity measurement. As I can see those are pretty advanced stuffs for most of us mortals to lay hands on such gear

 

[BJC]

The USACE may be the best place to look. Google up the Cold Regions lab and review some of the literature there. They have also been know to answer emails.
There is an Army tech manual on buidling in the artic ( actually several ) TM5 -852 is the one that comes to mind.
It's here.

http://www.usace.army.mil/publications/armytm/

Grounding is mentioned in some of the other manuals as well.
Basically on permafrost your building on glass. In the worst case you tie everying thing together and forget about the ground rods. You build your own ground system with copper on top of the ground. In a few months of the summer it's like a temperate region, but that doesn't last long.
The course at UW on cold regions engineering ( required for an Alaskan PE in any discipline) didn't go much into grounding.

 

[Skogsgurra]

Hey! Don't call land above the polar circle "the Arctic"!

That's practically where I live and I do not feel like a polar bear. We do have some polar Beer, though. It's named Norrlands Guld.

Is it the Arctic you are asking about? Or the tundra? Or just plain ordinary countryside at higher latitudes?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[pqsl]

Thank to all for sharing valuable information.
Practical information on what works and what does not in permafrost is scarce.
I will follow up all your suggestions.