Hi,

For ring-type (window-type) CT, do we need to size the CT short time withstand current at the same or above the system short time withstand current (short circuit level)? Any reference/technical explanation?

Thanks!

Please explain and detail your question a little bit, as it is rather unclear what you exactly mean with it.

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:)

Size it at 1.25 * the expected measured current without regard to peaks. Make sue the CT has an internal clamp.

Hi Credendovidis,

I will install a ring-type/window-type current transformer in a low voltage switchgear.
The system short time current withstand is, say, 80kA/1second. Do we need a current transformer with short time current rating 80kA/1second?

Thanks,

Quote:

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Originally Posted by Credendovidis

Please explain and detail your question a little bit, as it is rather unclear what you exactly mean with it.

Once you have posted details, contact me by private mail (click on my handle and follow instructions) to draw my attention. I will than reply here again.

:)

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Dear masgagong:

If fact, you are aware that window type cts are not directly connected in the circuit like wp cts. A bar primary conductor is just passed through the window of the ct. Cts are only insulated rated voltage of the system. Hence, there is no requirement of stc rating for window type cts. If the cts are of wp (wound primary) type then, these are directly conneted between current carrying bus bars hence, the are bound to have stc rating. (basically stc rating is meant for current carrying capacity of the conductorof ct) as well as mechanical strength of the cts as this may go under tremendous mechanical stress during fault conditions.