REF protection is a specialized, highly sensitive, and selective protection scheme for specific zones, whereas normal earth fault protection provides broader, less sensitive protection for the system. Both are essential for ensuring comprehensive fault coverage in electrical systems.
Purpose:-
1. REF Protection (Restricted Earth Fault): Protects a specific zone, typically within a transformer or generator, against earth faults. It ensures high sensitivity to faults within the protected zone while ignoring external faults.
2. Normal Earth Fault Protection: Monitors the entire system or feeder for earth faults and provides broader but less sensitive protection.
Zone of Protection:-
1. REF Protection: Operates within a tightly defined boundary (restricted zone), such as the transformer winding or a generator stator.
2. Normal Earth Fault Protection: Covers a wide area, typically the entire feeder or network.
Sensitivity:–
1. REF Protection: Highly sensitive, designed to detect low-level earth fault currents within its zone.
2. Normal Earth Fault Protection: Relatively less sensitive, often designed for higher fault currents across the system
Relay Configuration:-
1. REF Protection: Utilizes differential protection principles, comparing currents entering and leaving the zone to detect imbalances caused by faults.
2. Normal Earth Fault Protection: Usually based on residual current or voltage detection.
Applications:-
1. REF Protection: Commonly used in transformer and generator protection.
2. Normal Earth Fault Protection: Applied in feeders, cables, and general system earth fault monitoring.
Selectivity:
1. REF Protection: Very selective, operates only for faults within the defined zone.
2. Normal Earth Fault Protection: Less selective, may detect faults outside the immediate equipment.
