CT rating 1

[BrkfldEE]

I am try to specify current transformers for the protection of a 25MVA hydro generator. Can somebody help me understand what the CT ratings mean? C400? C800? T400?

 

[cranky108]

C means calculated, T means tested. And the number following is roughly the voltage at the knee point, at the maximum ratio.

It's a quick answer, and you probally need to read more about it.

 

[rbulsara]

Pretty much what cranky108 said.

Also see attached link:

http://pm.geindustrial.com/faq/documents/general/get-6498.pdf

Rafiq Bulsara

http://www.srengineersct.com

 

[dpc]

Those number refer to the accuracy of the CT at relay currents. The higher the better.

For high currents, the key to accurate current into the relay is how much secondary voltage the CT can produce before it saturates.

Keep in mind that for multi-ratio CTs, this accuracy rating applies ONLY to the maximum ratio. As you tap down, the accuracy goes down. So a 1200/5 C400 on the 600/5 tap is essentially a C200 accuracy, just as an example.

 

[prc]

ABB application guides may help you.

http://library.abb.com/global/scot/...HSM 9543 40-00en IT Application Guide Ed3.pdf

http://library.abb.com/global/scot/...e Outdoor Instrument Transformers Ed 5 en.pdf

 

[BrkfldEE]

Thank You, this helps.