NGR means Neutral grounding resistor. This is connected to
neutral wire to ground the extra leekage current.
Since in UT,UAT & ST star connection is used, that means
there are 4 wires (R,Y,B & N).Thus neutral is grounded with
any short circuits occur in stator or rotor then that short
circuit current will limitig and any erath fault occur in
rotor or stator then thats current will also limited value
by depending on resisance value
Neutral Earthing Resistors (NERs) – sometimes called Neutral Grounding Resistors – are employed in medium-voltage AC distribution networks to limit the current that would flow through the neutral point of a transformer or generator in the event of an earth fault. NERs limit fault currents to a value that does not cause any further damage to switchgear, generators or transformers beyond what has already been caused by the fault itself.