Installation of current transformers

[dennis323]

We recently discovered that the CT'S installed on our 13,2KV primary switchgear are the wrong ratio
and need to be changed.Which also makes the secondary CT's on our 5KV gear also incorrect.
Now the question,My co-workers think that 600volt
CT's placed around the conductors would be ok to use. I cannot find anywhere in the code book that addresses this issue. Please give some input.
Thank You.

 

[bennie]

Re: Installation of current transformers

Check with your local utility company meter man. Do not install anything until you talk to an experienced metering installer.

Charlie, the utility guy, will have better information, than I do.

 

[mclain]

Re: Installation of current transformers

If the conductors are insulated for the applied voltage I would think it would be safe. If not check with your meter man.

 

[bennie]

Re: Installation of current transformers

Dennis: I'm curious, what is the user doing changing CTs? Is this for power management equipment?

 

[dennis323]

Re: Installation of current transformers

The problem with the ct's was the ratio.
It was causing the differential protective relays
to trip.

 

[bennie]

Re: Installation of current transformers

I don't understand. Is this manufactured switching equipment? or is it site built?

 

[charlie]

Re: Installation of current transformers

Originally posted by Dennis323:
My co-workers think that 600volt CT's placed around the conductors would be ok to use. I cannot find anywhere in the code book that addresses this issue.

Instrument transformers are not much different than other transformers. A CT is sort of a regular transformer with a single winding primary. A 600 volt CT will work great if you don't have to have any wires attached to it and it is totally isolated from any grounded surfaces. Current is all that matters to the CT in this case.

With all that said, how do you attach wires to the CTs and mount the CTs? You will have a sharp voltage gradient and tracking from the 7620 volt phase wire to the mounting brackets and the secondary leads.

Bottom line, get the proper CTs.

 

[dennis323]

Re: Installation of current transformers

Bennie,
The one set of ct's are installed in the incoming
service switchgear,13kv,owner side not the utility side.
and the second set are installed in the main meduim voltage switchgear,5kv. The ct's are used with
protective relaying devices (differential relays).
The setup is 2 utility disconnects that feed two
transformers that feed two mains. 132kv to 4160kv
Dual ended switchgear. I hope this answers your questions. Thanks.