Short and Simple definitions

 Short and Simple definitions:

1) Differential Relay

Compares current at two points of equipment (like transformer). If difference is high → fault inside the zone → trips.

2) Distance Relay

Measures impedance (distance) between relay and fault point. Trips when fault occurs within a set distance.

3) Overcurrent Relay

Operates when current exceeds a preset limit → protects against overload and short circuit.

4) Earth Fault Relay

Detects leakage current flowing to earth → trips when insulation failure or ground fault occurs.

5) Numerical Relay

Modern digital relay using microprocessor → gives accurate, fast, and programmable protection.

6) Buchholz Relay

Used in oil-filled transformers → detects internal faults like winding insulation failure or gas formation.

7) Restricted Earth Fault Relay

Provides sensitive protection for a specific zone (like transformer winding) against earth faults.

8) Reverse Power Relay

Operates when power flow reverses (generator starts consuming power instead of supplying) → protects generator.

9) Under Frequency Relay

Trips when system frequency falls below safe limit → prevents system instability and load shedding.