Protection of Metering CT

It won't. It can't - the overcurrent device in the primary will operate first.

knee point voltage is low in metering CTs so that they saturate during fault currents. Thus metering instruments are saved from these fault currents due to saturation.

...and during a fault event, the important thing is to trip the overcurrent device at the earliest mossible moment. If this action should also turn off the metering, so what <rhetorical question - NNTR>?

Can you elaborate this sir???

The knee-point voltage is less applicable for metering current transformers. The concept of knee point voltage is very pertinent to protection current transformers, as they are exposed to very high fault currents. Since accurate meters are very sensitive to over currents, we do not want that a high fault current to pass through the meters, otherwise they will get damaged. We want the CT to saturate at high current so that the meter is safe.

Accuracy classes for CTs for various types of measurement are specified in IEC 60044-1 as Classes 0.1, 0.2, 0.5, 1 and 3. The class designation is an approximate measure of the CT's accuracy. The ratio (primary to secondary current) error of a Class 1 CT is 1% at rated current. If we try to measure 100A with a class 1 CT, the measured value may be either 101 A or 99 A or anything in between these range

So as you heard after installation of the TC and metering you can't take protective actions.

The best thing you can do is to choose wisely the instrumentation in the first place. The meters have maximum current of 10 or 20 times (maybe even more) the rated current so you can see the protection is built in itself.

PS: I will assume that you know the maximum short circuit current in your installation and that you chose the CTs and metering accordingly.

don't put any protection in a CT circuit. If you take the load off the CT it will generate very high and dangerous voltages which can in turn blow the CT.