Anodes on a copper ground

[huskerpower]

I have a piece of a copper gounding grid that is being isolated from the rest of the grid, and having a DC isolator put in place to protect the copper grid. My question is, does it matter if we leave the sacrificial anodes connected to the now-isolated portion of the copper grounding grid.

There is an active cathodic protection system in the area.

 

[brimmer]

huskerpower,

since no one has responded, I'll try to assist. What you are explaning does not quite make sense to me, or I don't have enough info. Perhaps explain the scenario (entire picture) and I might be able to help. When you state" having a DC isolator put in place to protect the copper grid" this does not make sense to me, as DC isolators are usually used to keep DC current from CP systems from going to the copper grid (i.e. you keep the CP current on what you are trying to protect rather than being lost to a copper grounding system, not the other way around).
As far as having sacrificial anodes attached to the copper grid, assuming they are zinc or magnesium, nothing will happen to the copper. The anodes will galvanically protect the copper, but if the anodes are meant to protect something else, please be aware anodes might not be providing enough current to protect what you want, and will be consumed faster.
When you say there is an active CP system in the area, there is an impressed current system in the area? The other anodes are seperate from, and there is a groundbed in close proximity to your copper? You would need to conduct CP interference testing to know if current from impressed system is getting onto the copper. Need details on this "active" CP system.

 

[huskerpower]

Here is the long version.

We are building an electrical substation adjacent to a natural gas plant. Because of land limitations we are using a portion of the existing plant fence to also serve as the substation fence.

Because the ground grid in a substation extends outside the substation fence for protection against touch potentials, we have taken the shared portion of the plant fence and electrically isolated it from the rest of the plant fence.

The gas plant has cathodic protection on it's underground pipelines. So we installed a DC Decoupler between the 2 grounding systems in order to protect the substation's grounding grid.

The portion of plant fence that is now part of the substation fence has a few anodes attached to it. Our initial recommendation was to leave those anodes in place with the logic that they would do no harm, and could even provide an additional layer of protection. If they are consumed quickly or slowly is of no consequence to us.

On the other hand we are not depending upon the anodes for protection, so if they were removed it would be of no consequence to us.

So, what is the best course of action for these anodes?

 

[cloa]

So these fences (metal stakes or reinforced concrete anchors) protude significantly into the ground?

 

[huskerpower]

I don't know the exact details of this fence since it was existing. However it is a typical 8 foot chain link fence, so the posts are probably 2 feet deep into a concrete base.

 

[brimmer]

Thanks. As far as the anodes, you are correct, won't affect anything, in fact, if this portion of the fence will be protected by the anodes (underground portion of posts), and anodes will even serve as additional ground if the fence does pick up any electrical current (say during a ground fault or something).
The DC decoupler I would suggest benefits them far more than you (it should be there though) as it will prevent them from loosing their DC current to your ground grid.
I assume this is normal AC power station? Being in the petroleum industry, I am a little concerned though at the proximity of the sub-station to their plant and piping. During a ground fault, you are most likely going to induce AC current onto their piping and thus into their plant. I would suggest that it would be on you the power company to conduct an AC study (after all we are talking about worker safety here, we don't want to kill anyone). I don't know what kind of current and voltage we are talking about, or if they have enough grounding to mitigate your AC effect if any. The power may also induce steady state AC onto the pipelines depending on configuation of power lines and pipelines, this could cause AC induced corrosion of their lines. Once built, testing should be done to ensure their pipelines have no steady state AC on them and above ground facilites (valves etc.) may have to have grounding grids of their own to protect during ground faults.