66kV sub transmission line - earth potential rise

[DrDrreeeaaa]

Hi All,

I am in a situation where a the distributor's 66kV line reticulates overhead through what is proposed to be my client's property.

The utility needs a 30m easement under the line. My client plans to install some underground piping (metal) under the lines in the easement. Ignoring the fact that, obviously, they are not allowed to build in the easement, what potential do you see for earth potential rise problems? Obviously I am talking about the case where the 66kV may drop to the ground.

The protection won't operate for around 5 or 6 seconds. Additionally there are many control systems and earth-sheathed cables on the site.

I don't have a good understanding of the possible problems with earth potential rise in a situation like this and I would be greatful for a description.

thanks.

 

[Marmite]

Personally, I can't see this being any different to the situation where a 66kV (or any other)line passes adjacent to the site, rather than across it. Presumably all the cable sheaths and extraneous metal is bonded together. The earth fault current will divide between the various impedance paths back to the source. In the event that a conductor falls this will cause a rise in potential locally relative to true earth, but if everything is bonded together then this shouldn't be a problem. The risk of a 66kV overhead line conductor falling in the first place is very low.
The protection clearing time you've given is also extraordinarily slow for 66kV.
Regards
Marmite

 

[jghrist]

Are you worried about earth potential rise being transferred by the pipeline to some other location? If the pipeline is bonded to the local earthing electrode at the other location, then there shouldn't be a problem.

Any dangers locally from earth potential rise will be insignificant compared to the danger of the live 66 kV line on the ground.

 

[DrDrreeeaaa]

Na all of my concerns are within 20 meters of the line (that is, this isn't a transportation pipeline, just an underground metal pipe connection between two sites across a road (the line follows the road)).

Yes well apparently the line is quite far from the substation and the protection is "not very good"

Anyway, surely every site that is near a power line would be subject to EPR problems should a power line fall to the ground. I have to say I don't understand the EPR problem at all - could someone help me out?