*RESTRICTING EARTH FAULT     PROTECTION*


~This type of protection is also called Balance Earth Fault Protection.  

~Instead of bringing out the six ends of the winding in a low capacity alternator, one end of the neutral is brought out by connecting the winding to the star from the inside and three ends of the line. 

~ Hence it is not possible to use a circulating current protection system.  

~Restricted Earth Fault Protection System is used in such 

~The star points of the alternator are connected to the earth resistor via a cr.  

~The line is connected as shown on the side.  The relay coil has a single winding.  

~When the stator winding of the alternator is healthy, the sum of the secondary currents of CT is zero at X and Y. 

~ There is no flow even from neutral.  Therefore the secondary current of CT is also zero.  

~Hence no current flows from the relay coil and the relay does not operate.  

~When an earth fault occurs in the winding of an alternator or an earth fault occurs at F, current flows from the secondary of CT, and the relay operates by passing current through the relay coil.  

~But when an earth fault occurs at F outside the protected zone, the same current flows in the secondary of both CT and CT so that current does not pass through the relay coil and the relay does not operate. 

~ This type of protection system is used where differential type protection cannot be provided. 

~The type protection system is also used as backup protection of differential protection system.