Sensitive Earth Fault Protection Relay

Check out the Wikipedia article on earthing, in particular IT systems.

Obviously.

For this, your unearthed system should have a neutral earthing transformer or a zig zag transformer having star connected primary winding with neutral terminal brought out for connecting to earth through an arc suppression coil ( Peterson coil ).

All the out going feeders of such a system should have a core balance current transformer ( CBCT ) through which,the 3 core armoured power cable( or single core cbles of all the 3 phases ) pass . The SEFR should be connected across the secendary terminals of this current transformer of respective outgoing feeder.

This arrangement is meant for protecting the feeder under single phase to ground fault conditions in the unearthed or non-effectively earthed powersystem.

If it is a numerical relay with zero sequence current sensing, then YES!