Protection Quick Reference Guide




Generator Protection


Transformer Protection


Distributed Electrical Resource (DER/DG) Protection


Distribution Protection




21 Phase Distance        
24 Overexcitation        
25 Sync Check  
27 Undervoltage
27B Bus Side Voltage Supervision        
27G Undervoltage (Neutral)        
27PP Phase to Phase Undervoltage        
27TN Third Harmonic Undervoltage (Neutral)          
32 Directional Power  
40 Loss of Field      
46 Negative Sequence Overcurrent  
46DT Definite Time        
46IT Inverse Time        
47 Negative Sequence Overvoltage    
49 Winding thermal protection        
50/27 Inadvertent Energizing          
50BF Breaker Failure    
50DT Definite time overcurrent for split-phase differential          
50(G/N) Instantaneous/Definite Time Overcurrent (Neutral)  
50GS Sensitive Ground Pickup        
50P Instantaneous/Definite Time Overcurrent  
51(G/N) Ground Inverse Time Overcurrent (Neutral)
51GS Sensitive Ground Inverse Time Overcurrent        
51P Phase Inverse Time Overcurrent      
51V Inverse Time Overcurrent (3-Phase with Voltage Control or Restraint)  
59 Overvoltage
59D Third Harmonic Voltage Differential          
59(G/N) Overvoltage, Neutral Circuit or Zero Sequence
59I Peak Overvoltage    
59PP Phase to Phase Overvoltage        
60FL VT Fuse-Loss Detection  
64(F/B) Field Ground/Brush Lift-Off Detection          
64S 100% Stator Ground Fault by 20Hz Injection          
67 Phase Directional Overcurrent      
67G Ground Directional Overcurrent        
67GS Sensitive Ground Directional Overcurrent        
67N Residual Directional Overcurrent    
67Q Negative Sequence Directional Overcurrent        
78 Out-of-Step Protection (Mho Characteristic)        
79 Recloser Relay        
81(O/U) Overfrequency/Underfrequency
81A Underfrequency Accumulation          
81R Rate of Change of Frequency    
87 Phase Current Differential        
87GD Ground (zero sequence) Differential        
87H Phase Differential High Set Overcurrent          
87T Phase Differential (Harmonic Restrained)          
AR Auto Restoration    
BM Breaker Monitoring    
CCM Close Circuit Monitoring        
HLT/MM Hot-Line Tag/Maintenance Mode        
TCM Trip (Aux Input) Circuit Monitor        
TF Through Fault          



Standard Feature
Optional Feature