Thanks for the reply.
I've done the calcs (this is an existing installation so I'm stuck with what I have).
The CT definitely saturates. I guess what I need to know is if I can count on the supervisory instantaneous overcurrent relay to pickup in spite of the CT saturation.
Blackburn says...
In the event that a transformer is subject to a catastrophic fault, one set of CTs will be exposed to very high current magnitudes which will drive them into saturation.
Is it safe to assume that since the opposing set of CTs will not enter saturation (picture a radial system), the differential...