Different Characteristic PS Class CT for Differential Protection

No.

Here's why:

"...if both knee point voltage of current transformer and magnetizing characteristic of CTs of both sides of Power Transformer differ, there must be a mismatch in high excitation currents of the CTs during (external) fault which ultimately causes the unbalancing between secondary current of both groups of CTs and transformer trips..."

From:

http://www.electrical4u.com/electrical-transformer/knee-voltage.php

Another good interview question meant to weed out non-Power Engineers.

Thank you for ur reply. Let me add this. The max secondary stabilizing voltage 2Vs=600v. Aprox. for both side. Let us say the protected eqpt is cable not transformer. Imag=30 mA at vk/2. This means, for max through fault current,the cts are not saturated and still in linear zone of magnetizing curve and hence the difference in magnetising current is still in mA level which may not be sufficient to operate the relay if we keep this in mind while doing relay setting. Please clarify.

Your welcome. Please clarify:

1. If this is a multipart question, are there any more parts;

2. Why you did not include all your knowledge in the original problem statement;

3. If this is any type of course work question.

4. Why you feel that the type of equipment makes a difference.

Thanks in advance for your reply.

Hi,

1 & 2. This is not a multi part question. I just thought my original question was more general and i thought the answers will be pointing out these various operating condition. The link u shared was dealing this issue only when cts are saturated. Thats why i wanted to tell my exact doubt.

3.No. Its very practical, i faced this problem.

4. Its just to make the discussion simple and the actual problem i faced was also for cable. Thats why.

Please clarify.