Sel SEL-421 - Page 79

R.1.37
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Ground Directional Element
Z2F is greater than 0:
Equation 1.3
Reverse Threshold
If Z2R is greater than or equal to 0:
Equation 1.4
If Z2R is less than 0:
Equation 1.5
32V
Directional Calculation
Equation 1.6
Forward Threshold
If Z0F is less than or equal to 0:
Equation 1.7
If Z0F is greater than 0:
Equation 1.8
Reverse Threshold
If Z0R is greater than or equal to 0:
Equation 1.9
If Z0R is less than 0:
Equation 1.10
Z2FTH 1.25 Z2F 0.25
V
2
I
2
------
• –• =
Z2RTH 0.75 Z2R 0.25
V
2
I
2
------
• +• =
Z2RTH 1.25 Z2R 0.25
V
2
I
2
------
• +• =
z0
Re 3V
0
I
G
1Z0ANG• 
*
• 
I
G
2
------------------------------------------------------------------------------=
Z0FTH 0.75 Z0F 0.25
3V
0
I
G
----------
• –• =
Z0FTH 1.25 Z0F 0.25
3V
0
I
G
----------
• –• =
Z0RTH 0.75 Z0R 0.25
3V
0
I
G
----------
• +• =
Z0RTH 1.25 Z0R 0.25
3V
0
I
G
----------
• +• =