Date:

Sunday, November 15, 2020

What are the IEEE/ANSI Device Numbers Used in Power System Protection ?

Generator Protection
Sample Application in Generator Protection 
(Photo Credit: General Electic)

In power system, the protection and control of equipment is represented by ANSI device numbers, with corresponding suffix letters when necessary, in relation to the functions they perform. The numbers are based on a system that is adopted by a standard for automatic switchgear by Institute of Electrical and Electronics Engineers (IEEE), and incorporated in American Standard C37.2-1996. 


This system is used  along with the diagrams that can be found in instruction books and in specifications. The International Electrotechnical Commission (IEC) standards 617 and 60617 also provide different symbols and terminology for most of the device numbers that are defined by C37.2. 


The second portion of this document provides a brief overview of a few of the more common IEC symbols used.


Read: Related Articles in Fault Analysis


1 - Master Element

2 - Time Delay Starting or Closing Relay

3 -  Checking or Interlocking Relay

4 - Master Contactor

5 - Stopping Device

6 - Starting Circuit Breaker

7 - Rate of Change Relay

8 - Control Power Disconnecting Device

9 - Reversing Device

10 - Unit Sequence Switch

11 - Multifunction Device

12 - Overspeed Device/Protection

13 - Synchronous-Speed Device

14 - Under-speed Device

15 - Speed or Frequency Matching Device

16 - Communication Networking Device

17 - Shunting or Discharge Switch

18 - Accelerating or Decelerating Device

19 - Motor Starter / Starting-to-Running Transition Contactor

20 - Electrically-Operated Valve

21 - Distance Relay

21G - Ground Distance

21P -  Phase Distance

22 - Equalizer Circuit Breaker

23 - Temperature Control Device

24 - Volts-per-Hertz Relay / Overfluxing

25 - Synchronizing or Synchronism-Check Device

26 - Apparatus Thermal Device

27 - Undervoltage Relay

27 TN  - Phase Undervoltage

27 X  - Third Harmonic Neutral Undervoltage

27 AUX - Undervoltage Auxiliary Input

27/ 27 X - Bus/Line Undervoltage

28 - Flame Detector

29 - Isolating Contactor

30 - Annunciator Relay

31 - Separate Excitation Device

32 - Directional Power Relay

32 L - Low Forward Power

32 N - Wattmetric Zero-Sequence Directiona

32 P - Directional Power

32 R - Reverse Power

33 - Position Switch

34 - Master Sequence Device

35 - Brush-Operating or Slip-ring Short Circuiting Device

36 - Polarity or Polarizing Voltage Device

37-  Undercurrent or Underpower Relay

37P - Underpower

38 -  Bearing Protective Device / Bearing Rtd

39 - Mechanical Condition Monitor 

40 - Field Relay / Loss of Excitation 

41 -  Field Circuit Breaker 

42 -  Running Circuit Breaker 

43 -  Manual Transfer or Selector Device 

44 - Unit Sequence Starting Relay

45 - Atmospheric Condition Monitor

46 -  Reverse-Phase or Phase Balance Current Relay or Stator Current Unbalance 

47 - Phase-Sequence or Phase Balance Voltage Relay

48 - Incomplete Sequence Relay / Blocked Rotor 

49 - Machine or Transformer Thermal Relay / Thermal Overload 

49 - RTD RTD Biased Thermal Overload 


Read: What are the Conditions in Selecting Current Transformer in Protective Relaying


50 - Instantaneous Overcurrent Relay 50BF Breaker Failure 

50 - DD Current Disturbance Detector 

50G - Ground Instantaneous Overcurrent 

50N -  Neutral Instantaneous Overcurrent 

50P - Phase Instantaneous Overcurrent 

50_2 -  Negative Sequence Instantaneous Overcurrent 

50/27 -  Accidental Energization 

50/74 - Ct Trouble 

50/87 - Instantaneous Differential 50EF End Fault Protection 

50IG - Isolated Ground Instantaneous Overcurrent 

50LR - Acceleration Time 

50NBF -  Neutral Instantaneous Breaker Failure 

50SG - Sensitive Ground Instantaneous Overcurrent 

50SP -  Split Phase Instantaneous Current 

51 -  Ac Time Overcurrent Relay

51 - Overload 

51G - Ground Time Overcurrent 

51N - Neutral Time Overcurrent 

51P - Phase Time Overcurrent 

51V - Voltage Restrained Time Overcurrent 

51R - Locked / Stalled Rotor

51_2 - Negative Sequence Time Overcurrent 

52 - Ac Circuit Breaker 

53 - Exciter or Dc Generator Relay 

54 - Turning Gear Engaging Device 

55 - Power Factor Relay 

56 - Field Application Relay 

57 - Short-Circuiting or Grounding Device 

58 - Rectification Failure Relay 

59 - Overvoltage Relay 

59B - Bank Phase Overvoltage 

59P - Phase Overvoltage 

59N - Neutral Overvoltage 

59NU - Neutral Voltage Unbalance 

59P - Phase Overvoltage 

59X - Auxiliary Overvoltage 

59_2 - Negative Sequence Overvoltage

60 - Voltage or Current Balance Relay 

60N - Neutral Current Unbalance 

60P - Phase Current Unbalance 

61 - Density Switch or Sensor 

62 - Time-Delay Stopping or Opening Relay 

63 - Pressure Switch Detector 

64 - Ground Protective Relay 

64F - Field Ground Protection 

64S - Sub-harmonic Stator Ground Protection 

64TN - 100% Stator Ground 

65 - Governor 

66 - Notching or Jogging Device/Maximum Starting Rate/Starts Per Hour/Time Between Starts 

67 - Ac Directional Overcurrent Relay 

67G - Ground Directional Overcurrent 67N Neutral Directional Overcurrent 

67P - Phase Directional Overcurrent 

67SG - Sensitive Ground Directional Overcurrent 

67_2 - Negative Sequence Directional Overcurrent 

68 - Blocking Relay / Power Swing Blocking 

69 - Permissive Control Device 

70 - Rheostat 

71 - Liquid Switch 

72 - Dc Circuit Breaker 

73 - Load-Resistor Contactor 

74 - Alarm Relay 

75 - Position Changing Mechanism

76 - Dc Overcurrent Relay 

77 - Telemetering Device 

78 -  Phase Angle Measuring or Out-of-Step Protective Relay 

78V - Loss of Mains 

79 - Ac Reclosing Relay / Auto Reclose 

80 - Liquid or Gas Flow Relay 

81 - Frequency Relay 

81O - Over Frequency 

81R - Rate-of-Change Frequency 

81U - Under Frequency 

82 - Dc Reclosing Relay 

83 - Automatic Selective Control or Transfer Relay 

84 - Operating Mechanism 

85 - Carrier or Pilot-Wire Receiver Relay 

86 - Locking-Out Relay 

87 - Differential Protective Relay 

87B - Bus Differential 

87G - Generator Differential 

87GT - Generator/Transformer Differential 

87LG - Ground Line Current Differential 

87S - Stator Differential 

87S - Percent Differential 

87L - Segregated Line Current Differential 

87M - Motor Differential 

87O - Overall Differential 

87PC - Phase Comparison 

87RGF - Restricted Ground Fault 

87T - Transformer Differential 

87V - Voltage Differential 

88 - Auxiliary Motor or Motor Generator 

89 - Line Switch 

90 - Regulating Device 

91 - Voltage Directional Relay 

92 - Voltage And Power Directional Relay 

93 - Field-Changing Contactor 

94 - Tripping or Trip-Free Relay 

50/74 - Ct Supervision 2

7/50 - Accidental Generator Energization 

27TN/59N - 100% Stator Earth Fault

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