Bảng mã hóa Relay theo ANSI. Thông thường, ta lựa chọn các relay bảo vệ theo chức năng bảo vệ, ví dụ như relay bảo vệ quá dòng, relay bảo vệ chạm đất, relay bảo vệ dòng rò, relay bảo vệ quá áp, relay bảo vệ thiếu áp, relay bảo vệ mất pha, relay bảo vệ đảo pha, relay bảo vệ thiếu tần số, relay bảo vệ quá tần số, relay bảo vệ lock rotor động cơ…
Tuy nhiên trong một số bản vẽ kỹ thuật, chức năng các relay bảo vệ thường được ký hiệu bằng số ví dụ 50, 50N, 51, 51N. Để chọn được đúng các relay theo các bản vẽ này ta phải hiểu được ý nghĩa các thông số ký hiệu relay này. Thông thường các relay được ký hiệu số như trên sẽ tuân thủ theo ký hiệu của bảng tên gọi relay theo ANSI như sau:
- 01 – Master Element
- 02 – Time Delay Starting or Closing Relay
- 03 – Checking or Interlocking Relay
- 04 – Master Contactor
- 05 – Stopping Device
- 06 – Starting Circuit Breaker
- 07 – Rate of Change Relay
- 08 – Control Power Disconnecting Device
- 09 – Reversing Device
- 10 – Unit Sequence Switch
- 11 – Multi-function Device
- 12 – Overspeed Device
- 13 – Synchronous-speed Device
- 14 – Underspeed Device
- 15 – Speed – or Frequency, Matching Device
- 16 – Data Communications Device (see note 5)
- 17 – Shunting or Discharge Switch
- 18 – Accelerating or Decelerating Device
- 19 – Starting to Running Transition Contactor
- 20 – Electrically Operated Valve
- 21 – Distance Relay
- 22 – Equalizer Circuit Breaker
- 23 – Temperature Control Device
- 24 – Volts Per Hertz Relay
- 25 – Synchronizing or Synchronism-Check Device
- 26 – Apparatus Thermal Device
- 27 – Undervoltage Relay
- 28 – Flame Detector
- 29 – Isolating Contactor or Switch
- 30 – Annunciator Relay
- 31 – Separate Excitation Device
- 32 – Directional Power Relay
- 33 – Position Switch
- 34 – Master Sequence Device
- 35 – Brush-Operating or Slip-Ring Short-Circuiting Device
- 36 – Polarity or Polarizing Voltage Devices
- 37 – Undercurrent or Underpower Relay
- 38 – Bearing Protective Device
- 39 – Mechanical Condition Monitor
- 40 – Field (over/under excitation) Relay
- 41 – Field Circuit Breaker
- 42 – Running Circuit Breaker
- 43 – Manual Transfer or Selector Device
- 44 – Unit Sequence Starting Relay
- 45 – Abnormal Atmospheric Condition Monitor
- 46 – Reverse-phase or Phase-Balance Current Relay
- 47 – Phase-Sequence or Phase-Balance Voltage Relay
- 48 – Incomplete Sequence Relay
- 49 – Machine or Transformer, Thermal Relay
- 50 – Instantaneous Overcurrent Relay
- 51 – AC Inverse Time Overcurrent Relay
- 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 (Earthing) Device
- 58 – Rectification Failure Relay
- 59 – Overvoltage Relay
- 60 – Voltage or Current Balance Relay
- 61 – Density Switch or Sensor
- 62 – Time-Delay Stopping or Opening Relay
- 63 – Pressure Switch
- 64 – Ground (Earth) Detector Relay
- 65 – Governor
- 66 – Notching or Jogging Device
- 67 – AC Directional Overcurrent Relay
- 68 – Blocking or “Out-of-Step” Relay
- 69 – Permissive Control Device
- 70 – Rheostat
- 71 – Liquid Level 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 Relay
- 79 – AC Reclosing Relay
- 80 – Flow Switch
- 81 – Frequency Relay
- 82 – DC Reclosing Relay
- 83 – Automatic Selective Control or Transfer Relay
- 84 – Operating Mechanism
- 85 – Communications,Carrier or Pilot-Wire Relay
- 86 – Lockout Relay
- 87 – Differential Protective Relay
- 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
- 95 – For specific applications where other numbers are not suitable
- 96 – For specific applications where other numbers are not suitable
- 97 – For specific applications where other numbers are not suitable
- 98 – For specific applications where other numbers are not suitable
- 99 – For specific applications where other numbers are not suitable
- AFD – Arc Flash Detector
- CLK – Clock or Timing Source
- DDR – Dynamic Disturbance Recorder
- DFR – Digital Fault Recorder
- ENV – Environmental Data
- HIZ – High Impedance Fault Detector
- HMI – Human Machine Interface
- HST – Historian
- LGC – Scheme Logic
- MET – Substation Metering
- PDC – Phasor Data Concentrator
- PMU – Phasor Measurement Unit
- PQM – Power Quality Monitor
- RIO – Remote Input/Output Device
- RTU – Remote Terminal Unit/Data Concentrator
- SER – Sequence of Events Recorder
- TCM – Trip Circuit Monitor
- SOTF – Switch On To Fault