Substation Fence Grounding 3

[Viceng]

Hi, I am looking for some recommendations: currently designing a substation which is enclosed by a fence (all standard),however, in this particular case a security fence (attached to one side of the substation fence) is extended in a large perimeter around the substation area (footprint enclosed by this security fence is actually larger than the substation footprint). I plan on running ground conductors on either side of the fence for its entire length and bonding the fence regularly to them, but my question is this: would you typically extend the crushed rock covering material from the substation along the entire length of this fence to assist with touch potentials in the vicinity of the fence?

Thanks for your input.

 

[Kiribanda]

esleigh,
In my opinion,if there is any possibility of getting the "TRANSFERRED POTENTIAL" on to the security fence from the substation fence when substation fence becomes live,then it is needed to have one meter wide crushed stone layer on either side of the security fence, because your calculated tolerable touch & step potential are based on the resistivity of the top layer.If the security fence is far away and no bonding to the substation fence,then no need of crushed stone layer or grounding.Anyhow if you could upload a sketch depicting the fence arrangement,then it is easy to comment more.

 

[PowerfulStuff]

esleigh,
I went through a similar situation last year. As Kiribanda says the transferred potential risk is as long as the fence. We ended up improving the substation earthing substantially - thus no gravel required and fence was OK as is.

regards,
PowerfulStuff

 

[Viceng]

Thank you both for your responses.

PowerfulStuff: when you say fence "was OK as is" did you not place ground conductors below the fence as well as no gravel?

Really it seems to come down to the top layer soil resistivity. If it is not low enough to ensure a surface potential nearly equal to grid potential, the crushed rock will be required. I am concerned that the touch potential, regardless of how good the substation ground resistance is, will be too high. I think as Kiribanda says the addition of crushed rock will be required.