Current, Differential and Power Transformers

Your question does not provide any information to even begin to answer your question. Provide all of the information you have regarding the transformer and either transmission or distribution systems.

I had not placed transformer specifics because I have yet to start searching products from suppliers. The transformer will serve 20000 KVA and is part of a distribution system.

the size and rating of cts to be placed on either end of the transformer depends on the burden of ct which in turn depends on the electromagnetic relay,connecting cables..etc in the circuit.

Are you talking about placing the CT on the neutral on either side, or on a phase on either side? I'm asking about placing it on the neutral

Power transformer neutral:REF CT:=MVA X 1000/(secondary star KV *1.73),select near higher ct ratio.

HT side:FLC higher CT ratio,similarly

LT side:FLC higher cise ct rario