(i) x% of the winding is unprotected, 

Voltage per phase = 3810 V 

Minimum fault current which will operate the relay = 150 A 

EMF induced in %x winding = 38.11*x V 

Earth fault current which %x winding will cause = 6.35*x A 

This current must be equal to 150 A 

Unprotected winding, x= 23.62 % 

(ii) The minimum earthing resistance required to provide protection for 90 % of stator winding = 2.54 ohm 


