Star Point of Current Transformer

star point is usually grounded bcoz in case if the burden gets disconnected from the CT secondary, it may act like a load to the secondary in turn preventing it from developing dangerous voltages. The side where the starpoint should be grounded decides the phase angle displacement and also the direction of protection( in case of directional protection, differential).

Could you please elaborate the second part of your answer(what decides the side of the star point)?

it s very big theory to elaborate here. You can refer some relay manuals for that. But be clear star point will be always towards the protected object. If it is made on the other side, then either you can change the polarity in relays (numerical relay) or u should add auxilairy CT in the secondary to correct the phase shift.