I'm actually designing a grounding systems for arctic climate.
This thread is a follow up of an older thread thread238-196015 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 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.
This thread is a follow up of an older thread thread238-196015 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 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.
