Substation Underground Cables

[timm333]

I have a question about underground cables of 13.8kV substation. There will be ground-grid whose depth would be 24”, and underground 13.8kV cables whose depth would be 30”. Does it mean that the cables will have to be buried before the ground-grid is installed? Or should we lay conduits below the ground-grid, and then the cables can be pulled in conduits later after the ground-grid is installed? Thanks.

 

[Dennis Alwon]

If the grid will be in the same vicinity as the cables then I can't imagine why you wouldn't install the cables first. Is there a reason not to do the cables first?

 

[Hv&Lv]

I have a question about underground cables of 13.8kV substation. There will be ground-grid whose depth would be 24”, and underground 13.8kV cables whose depth would be 30”. Does it mean that the cables will have to be buried before the ground-grid is installed? Or should we lay conduits below the ground-grid, and then the cables can be pulled in conduits later after the ground-grid is installed? Thanks.

Dig the UG conduits at 36” first, then install the ground grid.

Leave the ditch partially covered and dig in ground grid. No need to dress up only to dig again the next day…
We build substations for our utility and it works out perfect that way.

 

[timm333]

Yes it makes sense. The reason why I wanted to not do the cables first was because at this stage we don’t know that how many control cables would be required, so we don’t know that how many conduits would be required. But I think if we install couple of extra 4-inch conduits, then there would be no problem even if we have to install extra cables in the future.

 

[petersonra]

Yes it makes sense. The reason why I wanted to not do the cables first was because at this stage we don’t know that how many control cables would be required, so we don’t know that how many conduits would be required. But I think if we install couple of extra 4-inch conduits, then there would be no problem even if we have to install extra cables in the future.

How will you know where those additional cables are going to need to be run?

It always seems to me that the spare conduits end up being someplace where they're not needed.

Or worse yet there's no place to put the termination panels.

 

[timm333]

The substation does not have a lot of equipment, it only has 5 transformers and 1 switchgear. So we can lay one 4" extra conduit for each piece of equipment (total 6 extra conduits).

 

[Hv&Lv]

The substation does not have a lot of equipment, it only has 5 transformers and 1 switchgear. So we can lay one 4" extra conduit for each piece of equipment (total 6 extra conduits).

Wow! What size? You going to run all the control conduits over the top of the grid? There will be many more of them than there are 13.8kV runs. DC to the relays, fiber runs for SCADA, 120 to the relays and batteries, etc…

 

[timm333]

There is one large transformer of 13.8-4.16kV 20MVA, and several smaller transformers of 4.16kV-0.48kV 2.5MVA.

 

[timm333]

The conduits (power and control) will be below the ground-grid. Fiber optic cables can be run in power (or control) conduit.

 

[Julius Right]

In my opinion you have to build a web of conduits [or ducts] in a substation. In my experience in a power station, we made a web of cable duct and manholes. For a substation where the power cables run apart-may be in cable trays- and only control cables run underground handholes and conduits may be useful.

However, somebody experienced in this field has to do or to check the routing design.

 

[Hv&Lv]

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