Sel SEL-421 - Ground Directional Element Equations

R.1.36
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Ground Directional Element
Ground Directional
Element Equations
For legibility, these equations use vector quantities, defined in Table 1.32. The
analog quantities are listed in Table B. 2.
32QG
Directional Calculation
Equation 1.1
Forward Threshold
If Z2F is less than or equal to 0:
Equation 1.2
Table 1.31 Reference Table for Figure 1.21, Figure 1.22, and Figure 1.23
Name Description
z2 Negative-sequence voltage-polarized
directional element impedance calculation
Z2FTH Negative-sequence voltage-polarized
directional element forward threshold calculation
Z2RTH Negative-sequence voltage-polarized
directional element reverse threshold calculation
z0 Zero-sequence voltage-polarized
directional element impedance calculation
Z0FTH Zero-sequence voltage-polarized
directional element forward threshold calculation
Z0RTH Zero-sequence voltage-polarized
directional element reverse threshold calculation
32I Zero-sequence current-polarized directional element calculation
32IFTH Zero-sequence current-polarized
directional element forward threshold calculation
32IRTH Zero-sequence current-polarized
directional element reverse threshold calculation
Table 1.32 Vector Definitions for Equation 1.1 through Equation 1.11
Vector Analog Quantities Description
V
2
1/3 [3V2FIM] 3V2FIA Negative-sequence voltage
V
0
1/3 [3V0FIM] 3V0FIA Zero-sequence voltage
I
2
1/3 [L3I2FIM] L3I2FIA Negative-sequence current
IG LIGFIM LIGFIA Zero-sequence current
IP IPFIM IPFIA
a
a
The polarizing current angle quantity, IPFIA, is an internal quantity only and is not available
as an analog quantity.
Polarizing current
z2
Re V
2
I
2
1 Z1ANG• 
*
• 
I
2
2
-------------------------------------------------------------------------=
Z2FTH 0.75 Z2F 0.25
V
2
I
2
------
• –• =