Non-Conductive Fence for 138kV Substation

[jmsalinas1]

Has anyone ever used a non-conductive fence for a 138kV Substation or similar application? I ran accross AMICO but would like other options of possible. If anyone has ever used them can you please provide some feedback?

Currently I have conducted a ground study with CDEGS and in order to comply with safety limits for step and touch potentials I am having to add a ground conductor outer loop with crushed rock to the outside permiter of my substation fence but due to location of the substation this would involve moving my fence line in about 3' all the way around since the fence is located on the property line. I am looking for alternatives that is why I have started to consider non-conductive fence. Any information is greatly appreciated!

Thanks
Miguel Salinas

 

[hd2000]

What about a concrete / brick wall?

 

[cuky2000]

Concrete or brick wall could be considered as a conductive or semi-conductive fence.
Fiber glass fence could be an option. We used none conductive fence for a metropolitan utility in the North East coast. I will check the spec to see if we allow to share the info.
In other project similar to the one described, we restored the area outside the property line beyond the fence with 24 inches of crushed rock. This allow us to meet the required step and touch potential without perimeter conductor.

 

[jmsalinas1]

Thanks for the suggestions. Typically the type of set up we have now is outer loop 3' outside of fence permiter with 18"-24" of crushed rock like you have mentioned. The situation here is that the substation is located in the middle of the city with a bus stop about 2 feet from the fence line, apartment building on another side of the station and sidewalk on the remaining two sides. The issue here is that when the station was first build back in 1968 we should have moved the fence line in and left some space outside or installed an outer loop with some type of crushed rock. At present my options seem to be limited to moving the entire fenceline in about 3' which would be extremely expensive as we would have to tear out our existing fence cub and establish all new fencing and curb, or consider alternatives such as a non-conductive fence. Any more ideas?

 

[jghrist]

How about buying ROW and installing a perimeter loop under the sidewalk? You would have to ensure that step- and touch-potentials are OK without the crushed rock. It is probably in the street ROW anyway and you might not have to purchase the ROW. It might be less expensive to tear up the sidewalk than tear out the fence to either move it away from the property line or replace it with a non-conductive fence.

 

[cranky108]

If you tearup the sidewalk, you can use asphult over the ground loop. The Asphult is a poor conductor, and will allow you to meet your step potential.

 

[FPelec]

We generally use concrete fences for rural areas and/or bigger substations (with good earthing system), but for new substations in urban areas we often use fiberglass reinforced plastic fences. This also avoids some problems with local authorities because you have not to make any operation outside substation area.

Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[cuky2000]

We did test outside substations in metropolitan areas and we found that city side walks build with concrete rebar act fairly close to an equipotentiall surface. Also the underground metallic structures including other utilities such as water lines, gas, telephone, sewer, etc contribute to dissipate the ground fault current with (split factor). Actual test showed that is safe beyond a mansory fence without the conventional perimeter ground loop.

 

[stevenal]

Why remove the existing fence? Install a new fence inside and bond it to the grid with a perimeter ground loop, and remove all bonds on the existing exterior fence letting it float to local earth potential. Two fences should be separated so that both cannot be contacted simultaneously by an arm span. If two fences need to be joined, use an insulated fence section to do the job.

 

[jmsalinas1]

All I appreciate the replies.

stevenal - a new fence inside would be an excellent idea the only limiting factor is space. It is already a 3 Unit substation in an area that is roughly 200'x 200'. Moving the fence in about three feet is an expensive option but if we were to want to add an additionial fence within the station space would be the limiting factor.