CT Sizing 1

[mbk2k3]

I have a 600:5A CT, Rated C200. Total burden on CT circuit is 1.008Ohms.
C200 means, it holds 10% accuracy upto 20x secondary rated current.
If my fault level at this bus is 20kA, 20kA translates to 166A on the secondary, which is >20x secondary rated current.
Is this a clear-cut case that I need to increase the CT ratio, to a 1000:5A CT?

Am I right that it doesn't matter anymore that the total burden is 1.008Ohms, so the secondary voltage is 168V, still less than 200V, correct? This doesn't mean anything anymore since the accuracy of the CT is compromised?

 

[Mario53]

DM61850, I am not really sure why your answer would contradict mine as I totally agree with you. What I basically said is that his CT does not saturate because he'a got a small burden for his CT (1 Ohm) even though the secondary current is higher than 20x the rated current.

 

[DM61850]

Reading back through your post I think you meant to say "The reason you still have a secondary voltage below 200v is that your burden is only half of the maximum permitted".

The rated burden isn't the maximum allowed. You can have higher burden but you just won't get 20x rated with less than 10% error.

 

[Mario53]

Agreed. What I meant was "maximum permitted burden to maintain 20x rated current with less than 10% error". Obviously you can have a higher burden and lose accuracy.