utility PT/CT secondary circuit

[JLuc]

Hi all,

we need to connect utility's PT/CT secondary circuit to the meters (100 m away), we would like to use the same duct bank (concrete encased) we use for power cables (25kV),

Is this possible to do?

I'm worried about power cables interfering with the secondary signal from the PT/CT. I didn't ask utility measurement guys yet , just wanted to have your opinions/experiences first.

Thanks

 

[waross]

I have never see this done. I'm on the rod and I don't have my codes with me but I don't think that most codes will allow this. I expect that the utility will have standards that you must follow. Ask the utility rather than us. If you want an answer from the codes, where are you?

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

 

[davidbeach]

Dedicated conduit only. The only one that can really answer that question is your utility meter department. If they don't like the installation, they won't install the meter and your service won't be turned on.

 

[JLuc]

I'm in Canada.
it will be in dedicated conduit but common duct bank. I contacted my utility meter department, waiting for an answer.

Have you ever seen this type of installation? Power cables and meter cables are going to the same place...so I think it makes sense using only one duct bank.

I will update this thread as soon as I get an answer from utility guys.

Thanks

 

[rbulsara]

What Bill said is correct, however from technical point of view placing CT/PT secondaries in steel conduit and keeping more than 12 inches of separation, would sufficiently shield from the interferences.

 

[rbulsara]

Jluc:

I assumed you mean to only share the ductbank not the conduit or ducts with the power conductors. Separate conduit always..as david said.

 

[JLuc]

rbulsara:

Yes it will be separate conduit for sure, it is part of utility standards, just not sure if I can put these conduits in the same ductbank with power cables, still waiting an answer from utility.

JL

 

[alehman]

Most utilities have a length restriction, which may be exceeded at 100m. I've never heard of running one that far. Seems like you might need to consider some sort of remote reading meter if the utility will allow it.

 

[scottf]

alehman-

As long as the CT burden rating is sufficient, the length shouldn't be a problem. Runs of that long are quite common in substation environments.

Length is not an issue for the PT circuit.

 

[davidbeach]

scottf, alehman is correct, and your reasoning generally has nothing to do with it. Cable pulling, bends, that's the way we've done it, securing the run against tampering and etc. are reasons for limiting distance. Any meter installation away from the instrument transformers needs utility approval from day one.

 

[alehman]

I agree that the CT lead length can probably be handled with proper design. My concern was more along the lines of what David said.

 

[JLuc]

Utility length restriction here is 150m.

davidbeach you're right, the best thing to do is having your design approved by utility metering guys right from the start.

in my case they accepted it.

thanks for your comments

JL