Different Types of Relays & their Protection

[Rabert]

The different types of relays & their protection are:

1. Overcurrent Relay (OCR) – It operates when current exceeds a preset value due to overload or fault.

2. Earth Fault Relay (EFR) – It detects leakage current flowing to earth and trips the circuit.

3. Differential Relay – It compares currents at two points and operates when there is a difference indicating an internal fault.

4. Over Voltage Relay – It trips the system when voltage rises above the safe limit.

5. Under Voltage Relay – It operates when voltage drops below a preset level.

6. Thermal Overload Relay – It protects equipment from overheating due to prolonged overload.

7. Distance Relay – It detects faults based on impedance or distance from the relay location.

8. Buchholz Relay – It protects transformers by detecting internal faults through gas accumulation.

9. Reverse Power Relay – It operates when power flows in the reverse direction, protecting generators.

10. Negative Phase Sequence Relay – It detects phase imbalance that causes heating in rotating machines.

11. Frequency Relay – It operates when system frequency deviates from normal limits.

12. Restricted Earth Fault Relay (REF) – It provides sensitive protection for internal earth faults within a defined zone.

13. Over Flux Relay – It protects transformers from overfluxing due to high V/Hz ratio.

14. Directional Overcurrent Relay – It operates only when fault current flows in a specific direction.

15. Time Delay Relay – It introduces a preset delay before tripping to ensure coordination.

16. Instantaneous Relay – It trips immediately when fault current exceeds a set value.

17. Voltage Balance Relay – It detects voltage imbalance between phases.

18. Phase Failure Relay – It operates when one or more phases are lost (single phasing).

19. Lockout Relay – It acts as a master relay to trip and lock the system during major faults.

20. Auxiliary Relay – It supports control and interlocking functions in protection circuits.

21. Current Balance Relay – It detects imbalance in current between phases.

22. Under Frequency Relay – It operates when system frequency falls below the set value.

23. Over Frequency Relay – It trips when system frequency exceeds the safe limit.

24. Pilot Relay – It uses communication signals for protection between two ends of a line.

25. Gas Relay – It detects gas formation in transformer oil indicating internal faults.

26. Out of Step Relay – It protects generators from instability due to loss of synchronism.

27. Sync Check Relay – It ensures proper synchronization before connecting two systems.

28. Vector Surge Relay – It detects sudden changes in phase angle indicating faults or disturbances.

29. Trip Circuit Supervision Relay – It monitors the health of the trip circuit continuously.

30. Auto Reclose Relay – It automatically recloses a circuit breaker after a temporary fault.

31. Thermal Relay – It protects equipment from temperature rise due to overload.

32. Rate of Rise Relay – It operates when current increases rapidly, indicating a fault.

33. Directional Earth Fault Relay – It detects the direction of earth fault current.

34. Power Factor Relay – It operates when power factor falls below a preset value.

35. Voltage Restraint Relay – It modifies relay operation based on voltage conditions.

36. Voltage Controlled Relay – It operates depending on voltage magnitude in addition to current.

37. Current Differential Relay – It compares incoming and outgoing currents to detect internal faults.

38. Transformer Protection Relay – It provides comprehensive protection for transformers against multiple faults.

39. Generator Protection Relay – It protects generators from electrical and mechanical faults.

40. Motor Protection Relay – It safeguards motors against overload, faults, and abnormal conditions.

41. Busbar Differential Relay – It detects faults within the busbar zone by comparing currents.

42. Arc Flash Relay – It detects arc faults using light and current sensing.

43. Phase Sequence Relay – It ensures correct phase sequence to prevent reverse rotation.

44. Dead Line Relay – It detects absence of voltage in a transmission line.

45. Field Failure Relay – It operates when excitation in a generator is lost.

46. Under Current Relay – It detects abnormally low current conditions.

47. Sensitive Earth Fault Relay – It detects very small leakage currents to earth.

48. Over Temperature Relay – It trips when temperature exceeds safe limits.

49. Winding Temperature Relay – It monitors transformer winding temperature to prevent damage.

50. Oil Level Relay – It operates when transformer oil level falls below the required level.