Protection Quick Reference Guide




Generator Protection


Transformer Protection


DG Interconnection Protection


Distribution Protection




21 Phase Distance (Mho)        
24 Overexcitation (Volts/Hz)        
25 Sync-Check  
27 Undervoltage
27G Undervoltage (Neutral)          
27 (T/N) Third-Harmonic Undervoltage (Ground)          
32 Directional Power    
40 Loss-of-Field        
46 Negative Sequence Overcurrent  
47 Negative Sequence Overvoltage    
49 Winding thermal protection        
50 Instantaneous Overcurrent  
50/27 Inadvertent Energizing          
50BF Breaker Failure    
50DT Definite time overcurrent for split-phase differential          
50 (G/N) Instantaneous Overcurrent (Neutral)  
51G Ground Inverse Time Overcurrent          
51GS Sensitive Ground Inverse Time Overcurrent        
51N Inverse Time Overcurrent (Neutral)
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    
59X Multipurpose Overvoltage          
60FL VT Fuse-Loss Detection  
64F Field Ground          
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 Reconnect Time Delay        
79M Multi-Shot Auto Recloser        
81 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)          



Standard Feature
Optional Feature