Maximum current of a current transformer based on CT rating 1

[n00bEE]

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.

 

[111R]

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.

 

[n00bEE]

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.

 

[jghrist]

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.

 

[n00bEE]

jghrist,

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