Remote Ground - Ground Fault Currents - Affects on wildlife

[Dobber1978]

Does anyone know of any papers/articles that discuss remote ground grids / ground fault current and their affect on wildlife? Does anyone have experience with this?

Currently working on a substations design where the sub is basically on bedrock with high impedance to earth and can't achieve good connection to earth, to get around this a remote ground grid is being considered but have been asked by client if this will affect wildlife (frog, birds, small and large mammals, etc...) as the potential location for this is in a marshy wet area.

Thanks

 

[waross]

Anecdotally: Farmers have had problems when stray currents induce a very low voltage to ground on stock watering stations. A voltage loo low to detect by touch may prevent stack from drinking and lead to dehydration.
Try some google searches.
For grounding with poor soil conditions Google "Ufer ground".
After reading about the physics of Ufer grounds you may chose this solution.
Ufer grounding may be a text book solution for your grounding issues.
Wiki Ufer grounds

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[DBL-E]

Hi Dobber1978,
What are your design goals? Are you trying to meet touch and step limits? Are you trying to meet grounding system impedance target?
What is the current group potential rise in the area? By expanding the area of your grounding system you can dramatically reduce the impedance, the resulting ground potential rise, and the overall risk to wildlife, humans etc. Are you using a software that can consider that soil resistivity change?
I’m not aware a specific paper that can address the concerns with wildlife, but IEC 60479 does provide some information on livestock though I’m not sure if it provides a calculation method for determining voltage limits

Similar to waross response, there are a lot of white papers and articles for mitigation of stray voltages for livestock such as this USDA guide-
[URL unfurl="true"]https://naldc.nal.usda.gov/download/CAT92970513/PDF[/url]

Another options is ground wells, especially if you have soil resistivity measurements showing lower resistivity at greater depths.

 

[dik]

Hogs do not do well in electric fenced enclosures...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Dobber1978]

Hi DBL-E,

Thanks for response.

Design goal is step and touch safety and low impedance connection to earth as incoming lines have no return path.

Not sure what you mean by group potential rise, if this is the interconnection of the main sub grid with all of the other grids on surface, i.e. building perimeter, buried grounds to out buildings, etc..., we are planning to isolate the main grid with the site grids as this is a mine site and don't want any ground potential rise transferred to underground equipment, in Canada and this is limited to 100V, basically a main sub ground grid and a safety ground grid that the mine is connected to.

We are using CDEGS for the modeling of the system.

The deep ground wells were looked at but in the area of the substation (only area we have ground resistivity measurements) bed rock was hit and was very shallow with very high resistivity and the ground resistivity tests didn't show it improving at depth. Currently in the process of getting additional measurements taken away from the main sub to hopefully support a remote ground grid, looks like top soil cover does increase as we get away from substation area. If we find a suitable location the ground in the substation would only be designed for step and touch and the remote would be for step and touch and low impedance for our return path.

I will check out that paper.

Cheers,

 

[DBL-E]

Hey Dobber1978,
I meant to say *ground potential rise...sorry for the typo

Thanks for the goals, so I think of this as a 2 stage effort. For reducing the touch and step voltages, creating a tighter mesh in your system makes less voltage difference on the earths surface. In some more extreme cases (like someone installing on rock ...like yourself) you may need to use a tight ground mesh like [URL unfurl="true"]https://www.erico.com/category.asp?category=R3138[/url]. A tight mesh may create step voltage issues around the edge, that you can mitigate with ground rods, or even making rods/ground conductor at greater depths (think of a pyramid with a flat top), so your ground potential rise doesn't have a steep drop off.

For the impedance, extending the footprint/area of your grounding system is the most efficient approach. You can look at the ground potential rise before and after adding the remote ground. You can try several runs of grounding extending from your grid like:

Regarding the animals, I don't think there is going to be a concise paper on that (like there is for determining human current thresholds). If you do find something please report back as I'd like to read that too! Looking at the step voltages you can determine if you are introducing more hazards to the area or if its reducing when you add your remote ground. Changing the buried depth lower can help avoid step potentials while reducing your system impedance too.

 

[itsmoked]

Welcome to Eng-Tips DBL-E.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dik]

From a non-smokie, too...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[waross]

Thinking out of the box.
Ufer grounds are typically near the surface.
Deep well grounds often use GEM, Ground Enhancement Material.
Has anyone used concrete instead of GEM in a deep well ground?
Is it possible to do a couple of test holes for an on-site evaluation of deep Ufer Grounds?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[DBL-E]

Thanks itsmoked/Dik for the welcome! I've been seeing this forum for my own random questions and figured I can help out here!

Waross, I know there are various vendors for ground well and trenching fill material. I have not just used concrete, but it seems like a valid idea.

For onsite testing, its cheapest to start with soil resistivity measurements (deeper is typically better). I have done testing on the first well of several in the design to adjust the length of other wells based on the field test results. A lot the cost for ground well is getting the drill out to site, but it was worth testing to see if 300+ feet could be reduced to 200 ft depth.

 

[waross]

DBL-E
Have you had the opportunity to compare deep well GEM treatment with deep well Ufer treatment?
What results?
Thanks

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[DBL-E]

Hi Waross,
No I haven't had the chance, but I'll keep a lookout for firms that may do those sort of A B comparisons.

 

[Fischstabchen]

It is a feature of SWER ( single wire earth return ) systems when the path to the earth return is weak or there are multiple users close together causing a voltage gradient. SWER systems are cheaper to serve rural customers due to only needing to run one wire but in the U.S. utilities have phased it out due to being sued over and over by farmers who claim that the system is reducing their milk production even after a ground mat has been put down in the cow's living area. Not much of a gradient is necessary to agitate cattle but much of the time the farmer was looking for someone to recoup his losses.

Check out the standard IEEE 80 for information on substation grounding. Like waross said Ufer is an option and it was a type of grounding developed for in the deserts during the Manhattan Project. There are chemical salts and bentonite that can be used to reduce soil resistivity. In my experience, just having a larger grid often mitigates most high earth return paths. The grounding grid though is for protecting workers inside of the substation if there is a fault and not for normal operation. You don't have to stray far from the substation before the voltage gradient is reduced to safe levels. Even then, fault are so infrequent and short inside of substations that I would not ever put much thought into its affect on wildlife. There are so many other things that are more dangerous to wildlife like cars on the roads.

 

[srini1785]

Noob question Alert!

Can't you not drill down the bedrock until you hit proper earth?.

 

[waross]

I have read a couple of reports of stray voltages affecting livestock.
In all the reports where a cause was located it was a low voltage impressed on a metallic watering trough.
The voltages were very low, often undetectable by touch, but a cow's mouth is apparently very sensitive to very low voltages.
In some cases the fault leakage was in the farmer owned wiring to the freeze protection heaters.
In some cases the voltage was induced by an overhead power line.
I would worry more about wildlife drinking from streams directly under the transmission line rather than about remote step voltages.
But, that said, station grounds are typically enclosed by the station fence. You may consider an animal barrier around the remote grounds.
There may be a hazard to any wildlife in close proximity to the remote grounds in the event of a ground fault on the transmission line.
If you use a barrier, a regular application of herbicide inside the barrier may avoid hungry animals trying to cross the barrier.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Can't you not drill down the bedrock until you hit proper earth?.

Bedrock is bedrock. The challenge is to make good contact with the bedrock. Hence to use of Ground Enhancement Material in deep well grounds.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jghrist]

I don't think that this is a situation where stray voltages would be a problem. Stray voltages that cause problems with dairy cows are a result of constant earth currents and you will only have earth current during faults.

If you keep step- and touch-voltages within IEEE Std 80 limits for humans, you should be OK for animals. You can model remote grounds with CDEGS.

 

[Fischstabchen]

jghrist,

You do have constant ground currents due to system imbalances but I doubt that would ever been enough to be an issue. I too am of the opinion that it is a non-issue as faults are rare and you have to be fairly close to the sub for it to even be felt. There is probably more issues with wildlife getting into the substation and faulting equipment if you don't have stuff to stop snakes and whatever.