SELECTION OF PROPER CURRENT TRANSFORMER IS ONE OF THE IMPORTANT PART OF A PERFECT PROTECTIVE SYSTEM. IF THE PROTECTION IS DONE BY DIFFERENTIAL THEN IT HAS THE MOST IMPORTANCE.....

"WHAT IS RESTRICTED EARTH FAULT PROTECTION??". BUT MORE IMPORTANT THAN "WHAT" IS "WHY" RESTRICTED EARTH FAULT PROTECTION

The name suggest the principle. It is restricted. What does it mean and why we need such restriction. Lets go deeper.

It is restricted between a certain zone. That means the protection function will work only within a specified zone that is pre-determined.

Suppose you have selected a certain boundary, this restricted earth fault protection (REF) will detect earth fault only within that range. Earth fault out side the boundary will not be detected by the REF scheme.

Protection against earth fault is very much essential for the machine having a core such as generator, transformer & motors. The most occurred and severe earth fault happens when insulation of winding get damaged, and it touches the core of the machine. Since core is kept earthed, this situation causes an Earth fault.