Excavation work around a in-service substation ground grid?

[mbk2k3]

44kV system (3 phase, 3 wire).
This is an existing substation plant that is in-service and we can't de-energize due to customer uptime requirements.

While doing some excavation work for ductbanks/concrete pads/etc, the civil contractor has run into the existing ground grid (done years ago by others).
We have a drawing of the existing system, but no ground grid study. There are several grids and loops all tied together. Only a small part of the grid is conflicting with our scope of work.

We have a plan to use temporary ground straps and throw in an equivalent number of rods so we can eliminate this small part of the grid that is causing the conflict. But i'm not sure how this is going to effect step/touch/GPR levels and whether its safe to work while its live?

How do others work around this issue?
Is it safe to work on buried ground grid conductors while the 44kV system is live and energized?

 

[Palletjack]

How much of it have you ran into?
I have dug in energized substations, we try to make it a point to never cut the grounds.
If we cut one with the backhoe, we stop, and repair immediately with PPE on.
Can’t you put whatever it is your installing under or over it?

 

[davidbeach]

Do the excavation in the yard with a vacuum truck.

 

[waross]

You beat me to it David.
A good vacuum truck with a high pressure water jet is the way to go.
We can't advise you on modifications to the ground grid without a lot more information and possibly not even then.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bacon4life]

Without high resistivity yard rock to limit touch and step potentials, you need PEE rated for the appropriate voltages during any excavation inside a substation. Prior to making any cuts, ensure that there is a nearby alternative path in good condition. Ground grids can corrode away, so verifying the conditions it is important before making any modification.

 

[mbk2k3]

thanks for the responses guys.

the stuff going in can't be installed around the ground loops. so we can't just vacuum truck out and install new ducts/etc. we def. have to cut and scrap the grounds.

i'm planning on installing more wires/loops and rods in the area (to ensure that we have as much or more copper in the ground), interconnecting, testing and then cutting the interfering areas (with appropriate PPE as stated).

 

[waross]

For CYA you may want to consider having an outside engineer or firm design and stamp the changes to the ground grid.


Bill
--------------------
"Why not the best?"
Jimmy Carter