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Maximum current of a current transformer based on CT rating

Maximum current of a current transformer based on CT rating

Maximum current of a current transformer based on CT rating

(OP)
Hello all,

How does one find the maximum current rating of a current transformer? Say the current transformer ratio is 3000:5 and it is C400 rated. I know that the CYYY rating is a measure of the CT's performance, but have no idea if I can calculate the maximum current rating of the CT with this information.

Also, is there a maximum current rating for both sides of the current transformer (primary and secondary)?

Any suggestions or readings would be greatly appreciated.

RE: Maximum current of a current transformer based on CT rating

It will be the rated current multiplied by the thermal rating factor (TRF). If the TRF is 2.0, it will handle 6000A through the primary and 10A through the secondary continuously.

RE: Maximum current of a current transformer based on CT rating

(OP)
Thanks for the information, 111R. It looks like the thermal factor will need to be obtained from a manufacturing specification sheet. The C400 standard won't tell me the thermal factor.

RE: Maximum current of a current transformer based on CT rating

The thermal rating factor times either the primary (3000 A) or secondary (5 A) rating will give you the continuous current rating. The C rating will, in combination with the burden, tell you how much fault current you can have without saturating the CT. If the secondary current during a fault times the burden impedance exceeds the C rating in volts, the CT will saturate and you will lose accuracy.

RE: Maximum current of a current transformer based on CT rating

(OP)
jghrist,

Thanks for the information. Both of these responses were very helpful and I have a better understanding of CT ratings now.

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