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Author: Admin | 2025-04-28
Per Hertz Relay (in some old analog applications, a 59 and an 81 device would be chained together as a 59/81 to implement the equivalent of V/Hz protection)25 – Synchronizing or Synchronism-check Device26 – Apparatus Thermal Device, Temperature Switch27 – Undervoltage Relay27P - Phase Undervoltage27S - DC Undervoltage Relay27TN - Third Harmonic Neutral Undervoltage27TN/59N - 100% Stator Earth Fault27X - Auxiliary Undervoltage27 AUX - Undervoltage Auxiliary Input27/27X - Bus/Line Undervoltage27/50 - Inadvertent Energization28 - Flame Detector29 - Isolating Contactor30 - Annunciator Relay31 - Separate Excitation Device32 - Directional Power Relay32L - Low Forward Power32H - High Directional Power32N - Wattmetric Zero-Sequence Directional32P - Directional Power32R - Reverse Power33 - Position Switch34 - Master Sequence Device35 - Brush-Operating or Slip-ring Short Circuiting Device36 - Polarity or Polarizing Voltage Device37 - Undercurrent or Underpower Relay37P - Underpower38 - Bearing Protective Device / Bearing Rtd39 - Mechanical Condition Monitor (Vibration)40 - Field Relay / Loss of Excitation41 - Field Circuit Breaker42 - Running Circuit Breaker43 - Manual Transfer or Selector Device44 - Unit Sequence Starting Relay45 - Atmospheric Condition Monitor (fumes, smoke, fire)46 - Reverse-Phase or Phase Balance Current Relay or Stator Current Unbalance47 - Phase-Sequence or Phase Balance Voltage Relay48 - Incomplete Sequence Relay / Blocked Rotor49 - Machine or Transformer Thermal Relay / Thermal Overload49RTD - RTD Biased Thermal Overload50 - Instantaneous Overcurrent Relay50BF - Breaker Failure or LBB (Local Breaker Back-up)50DD - Current Disturbance Detector50EF - End Fault Protection50G - Ground Instantaneous Overcurrent50IG - Isolated Ground Instantaneous Overcurrent50LR - Acceleration Time50N - Neutral Instantaneous Overcurrent50NBF - Neutral Instantaneous Breaker Failure50P - Phase Instantaneous Overcurrent50SG - Sensitive Ground Instantaneous Overcurrent50SP - Split Phase Instantaneous Current50Q - Negative Sequence Instantaneous Overcurrent50/27 - Inadvertent Energization50/51 - Instantaneous / Time-delay Overcurrent relay50/74 - CT Trouble50/87 - Instantaneous Differential51 - AC Time Overcurrent Relay51C -
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