Fence grouding at a generating facility
Fence grouding at a generating facility
(OP)
I have recently been given the task to design and construct a grounding system for a metal chain link fence at a generating facility. I have never done this before so I'm looking for some help. The fence is 300 feet long and is more or less a straight line. What value should I be targeting for a fair ground resistance? I plan on connecting to the station grounding system. Could that be a bad idea?
The voltage of the generators is 13.2 kv, and is then stepped up to 230KV before it leaves the staion. The power generated is about 400 Mega Watts. Our generators are high impedance grounded and the transformers are soildly grounded.
Thanks in advance,
-TurbineGen
The voltage of the generators is 13.2 kv, and is then stepped up to 230KV before it leaves the staion. The power generated is about 400 Mega Watts. Our generators are high impedance grounded and the transformers are soildly grounded.
Thanks in advance,
-TurbineGen
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If it is broken, fix it. If it isn't broken, I'll soon fix that.






RE: Fence grouding at a generating facility
On a lighter note, I had a similar assignment and had a huge fight with the contractor when I asked him to remove the vinyl coated fence he installed and replace it with a non coated type.
RE: Fence grouding at a generating facility
RE: Fence grouding at a generating facility
Breaking the fence continuity by installing an isolating section at the edge of the main grid might help. But ground cables on both sides of the fence are probably needed, out about a meter and 0.5 - 1 meter deep. Anyone touching the fence should have a ground grid under their feet.
A simulation analysis is needed to get an accurate picture of the hazard. Read the applicable sections of IEEE 80 for advice, but it is sketchy.
RE: Fence grouding at a generating facility
What is wrong about Vinyl coated fence ?
Thanks
RE: Fence grouding at a generating facility
RE: Fence grouding at a generating facility
RE: Fence grouding at a generating facility
Basically if you procede as described in RCwilson's post only the wires that are scraped are grounded.
RE: Fence grouding at a generating facility
"the vertical wires may be insulated from one another"
So how does this matter. I am working on a substation project and fencing might be coming shotly in my way.
Is there are any literature available to get a better feel for it.
Thanks
RE: Fence grouding at a generating facility
The fence runs away from the power station 500 feet or so. The plans I made call for a non conductive fence after 300 feet as there are overhead lines that cross this fence 125 feet away from the plant (giving an extra 175 feet of grounded fence beyond the lines). The grounding cable I'm using is a 500kcmil cable connecting the ground rods only on one side of the fence (the other side is a rocky cliff). About 50 feet of the fence runs alongside the station ground and then goes outward from there.
Should I isolate the fence that runs beyond the grid by installing a non conductive fence between the metal fence beside the station and the metal fence that runs outward? Also, it appears I can only run a ground cable and rods on one side of the fence as the other side is a rocky cliff. If I do isolate part of the fence, how do I lower it's resistance when I can only run cable on one side? This fence encapsulates a parking lot which (and I have yet to verify this) has a 500kcmil loop around it on three sides (the missing side being the fence side). If that loop is in fact there and connected to the station ground, should I connect to it? Or should I try to isolate the fence run entitrely? I tried my best to make a "text picture" below to give a description of what I have.
============================================
fence |
(station)| |
| |
______| |
| |
| Existing cable |
|_____________|
Again, thank you all for your support.
-TurbineGen
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Fence grouding at a generating facility
RE: Fence grouding at a generating facility
RE: Fence grouding at a generating facility
RE: Fence grouding at a generating facility
Turbine Gen- Based on your sketch I recommend grounding the fence and connecting the ground to the existing ground wires around the parking lot. Not connecting it could create more of a hazard. Where the fence leaves the parking lot and substation area, an insulating section may prevent transferring the grid GPR outside the grid area.
Since one side of the fence is a cliff, it may not be practical to put a buried conductor on that side. You would rely on the ground conductor on the other side to keep the fence near the local ground potential. We ground the fences to prevent someone from getting shocked during a HV ground fault when their feet on the ground and their hands on the fence are at different potentials due to the current flow in the ground. With a cliff on one side, the odds of someone standing there during a fault are very small. I'm guessing that the current flow in the ground at the top of the cliff would also be reduced. (Where is it going to flow to?)
There are other factors to consider – what is the GPR of the grid, what is the maximum allowable touch potential given your fault clearing time and type of soil at the fence? Evaluation of all the criteria will help you evaluate the risk and mitigate it where necessary.
GT Startup- Good point about isolated fence fabric. I'm wondering if the vinyl coating also reduces the touch potential hazard. The uncoated posts and horizontal pipes are connected to the buried rod or ground wire but the fence fabric would be floating.
This is a problem near the HV lines where the fabric can get potentials induced. But I don't see it as a problem on the plant perimeter fence that is 50-100 meters away from any line. The insulated fabric would not transfer the GPR so it would not create a touch potential hazard and there is nothing in the area to energize the fabric.
RE: Fence grouding at a generating facility
If the existing cable is not connected to the station grid, it may still have a high voltage induced in it. I suspect that you will be better off connecting the existing cable to the grid and bonding it the the fence. If one of the lines falls on an isolated fence, there will be a larger danger.
If the 175 feet of fence beyond the parking lot is truly non-conductive, like a wood fence, then I wouldn't worry about it. If it is vinyl coated steel, I wouldn't consider it non-conductive.
On the insulted fabric question, if the coated wires are next to grounded wires or surrounded by a grounded frame, I'd treat them as if they were the same potential as the frame. What other voltage would they be? The vinyl coating will not reduce the touch-potential hazard, but in practical terms, I don't think it will make it worse.
RE: Fence grouding at a generating facility
“The intent of Rule 092E is to provide an intentional, conductive path to earth for all metallic fence components,
either by direct connection to a grounding conductor or by bonding to another suitable grounded fence
component. Note the definition of bonding: “The electrical interconnection of conductive parts...”
RE: Fence grouding at a generating facility
Here's the link
http://standards.ieee.org/nesc/NESCIR528.pdf
RE: Fence grouding at a generating facility