Differential & restricted earth fault protection of transformer
Differential & restricted earth fault protection of transformer using one set of PS class CT at star side, i.e with the help of same PS class CT both differential & high impedance REF protection can be achieved or not !
The relay to be used is numerical type which has both differential & REF features.
Answer: Usually CTs rated to be used for differential protection will not be as sensitive if applied for earth fault protection, due to the high primary current rating. Loading up the secondaries of these CTs with other burdens of questionable value also risks the best protection you have for your transformer.
Earth fault down to 10% of the windings can be achieved by monitoring current or voltage directly in the neutral, leaving the poor protection (?<50% of the windings) available by measuring the line current out of the protection scheme altogether.
Sometimes belt & suspenders can create more risk than K.I.S.S. If you supply the model of the relay you have in mind, and the details of your high impedance grounding, then more help may be available.