Substation Property Line Fence Fail IEEE80

[RSChinn]

I cannot pass IEEE80 touch potential criteria at a substation fence built on top of the property line adjacent to neighbors. I cannot move the fence inward three feet in order to get a horizontal ground conductor three feet out from it as this restricts our ability to get to the substation equipment. We thought of a vinyl fence but the fence vendor will not guarantee any dielectric properties of the plastic coating as his coating is only for weatherization/ aesthetics purposes. Any suggestions???

 

[cranky108]

How long has the substation been there? Have you consitered a wall?

 

[RSChinn]

To crany108: The substation is about 50 years old and built when the entire world did not have the design tools we now have to understand that you generally need a three foot ground conductor outside the fence to mitigate touch potentials. A wall would make the neighbors backyard resemble a prison yard (especially with the barbed wire on the top). I believe it is one thing to leave as is alone by "grandfathering" the situation, but I am adding a switchgear and improving the inside the fence grounding grid which constitutes major rework obligating us to follow latest codes and standards I believe.

 

[stevenal]

Grandfathering wouldn't mean much if a neighbor got hurt. Think about the wall idea a bit more. The neighbors may find an attractive one might be preferable to looking at switchgear. Suggest building it tall enough that barbed wire isn't needed.

 

[pwrtran]

Sometimes ground grid might be over designed. Have you taken consideration of current splitting factor by all feeder neutral conductors going out of the station?

 

[JG2828]

Have you tried AMICO non-conductive fencing? Your situation seems to be what it is designed for.

 

[JG2828]

This link is a little more useful for the AMICO fences. It says they are tested up to 660kv.

 

[RSChinn]

To pwrtran- The split factor has been inclusive already and still the Touch potential fails at the fence.
To JG2828- Your thoughts about using AMICO non-conductive fencing is fantastic! This brochure showing it already installed at a substation is a convincing element to use it. Some of my colleagues question the ability to break in as it is composite plastic... but then so can using a bolt cutter on a steel mesh.

Anyone with thoughts contrary to using the AMICO fence?

 

[EEJaime]

RSChinn,
Well there's always the fact that anyone consciously breaking into a high Voltage substation to steal copper will get a grand dose of what is deserved. But it does pose a concern about infrastructure security. But as you've already stated, a chain link fence is not exactly a maximum security barrier. I think the product looks extremely viable and would be an improvement aesthetically over chain link. I don't think the neighbors would object at all.
Regards,
EEJaime

 

[racookpe1978]

To be honest, would a person be able to break in through the plastic (non-conductive fence? Yes.
Could that same felon/trespasser break through a chain link fence?
Yes.

Would that person "see" an obvious difference when he drove past this new plastic fence to say "Hey! I can now break through that new fence and get killed trying to steal electrified copper!" If the thief can't see a big difference between the new fence and the old fence, and he doesn't know there is a difference in strength/cutting resistance between the old and the new fences, why would he now try to to break through the new one if he has not been breaking through the old one?


OK, so buying the 3 foot strip has been ruled for some reason.

Also: Can you get a "utility easement" type of a rental agreement with the current landowner to bury a grounding wire under his property? After all, you would be the one paying, he can still use the property - even TX farmers don't plow all the way to the fence! - and the new wire is undergrouand and NOT a visual obstruction.

 

[7anoter4]

I agree with EEJaime except the fact that anyone who will try to stole copper from the grounding grid will get “what is deserved”, since that could be only in the extreme case of a maximum grounding fault and this occurs very-very seldom.
The racookpe1978 proposal of getting a "utility easement" type of a rental agreement could be a better solution than trying to insulate the fence [IMO].

 

[Electic]

Surface voltage gradient is what you wish to limit. Is there any hope to limit this if a conductor were buried deeper below the fence, to disperse the current further in the ground and with more of a protective soil layer between that and a person's feet. Transfer potential to the fence would remain just as high, so perhaps the fence could be well grounded to another depth, but isolated from the main grounding grid? I could visualize a heavy substation ground perimeter conductor at 6-9' below grade, and the fence ground, isolated from the substation ground, at say 3', straight below the fence.

This is not a recommendation without more work completed by experts and researchers, and the custom solution might still constitute a legal liability simply for not being normal.

 

[karls2]

I am agree with electic in some case in the french NF C 13-200, les figures 41H et 41J it's admit that you can have a separate grounding loop for the fence (under conditions).
Anyway this separate grounding will be influence during a fault, but It may help you to limit the touch voltage in this area.