CT Burden: Long cable length

[HamburgerHelper]

Aside from specifying larger cables to reduce the total burden on long paths, does anyone make something like a current mirror to reduce the burden on a CT by not forcing it to do the driving? I see using something like GE's Brick can do something like this by going 61850 and returning the measurements with digital but I think 61850 would be a hard sell with it being new.

 

[HamburgerHelper]

Something like a current transducer that is used in protection?

 

[cranky108]

I have only seen something like this for a line differential.

Have you looked at optical CT's?
Higher burden capable CT's, or CT's in series?

 

[HamburgerHelper]

No, I haven't looked at optical but the power that be don't like trying anything new or different.

Maybe, they will get different CT's. I hadn't thought of putting them in series if possible but then you tie up both sets of CTs.

I thought there might be something just like a transducer since that resolves any issues you have with the burden and that isn't a new problem. The Alstom transducers I have found that could be used have too much lag for transmission relaying anyways.

 

[Marmite]

I'm curious as to why you are coming across burden issues? They used to manage years ago with huge AIS outdoor transmission switchyards, long secondary cabling distances, high burden electromechanical relays rated at 5A. These days switchyards are much smaller and burdens are generally much smaller. What is the issue?

Regards
Marmite

 

[HamburgerHelper]

It isn't my project but I was curious what's possible. The distance from the control building to the CTs is 1000 ft and there is a lot of fault current.

 

[Skogsgurra]

If you can live with the increased tolerances, it is usually possible to use an intermediate 5:1 A CT and then a 1:5 A at the receiving end. Usually OK for protection and indication, but not for metering. On the other hand - why put protection so far away?

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[stevenal]

Rogowski coils aren't very new, and the voltage signal provided would not have the burden issue.

 

[scottf]

1000 feet it not THAT uncommon.

#10 AWG is 1ohm/1000ft.

What burden are trying to get it down to?

Using #8AWG or #6AWG is pretty simple, or you could double-up #10AWG.