Schweitzer Engineering Laboratories SEL-421-4 - Page 203

5.43
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Ground Directional Element
Ground Directional Element Equations
For legibility, these equations use vector quantities, defined in Table 5.38. The
analog quantities are listed in Section 12: Analog Quantities.
32QG
Directional Calculation
Equation 5.15
Forward Threshold
If Z2F is less than or equal to 0:
Equation 5.16
If Z2F is greater than 0:
Equation 5.17
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
Ta b l e 5 . 37 Ref e re n ce Ta b le fo r
Figure 5.23 , Figure 5.24 , and Figure 5.25
(Sheet 2 of 2)
Name Description
Table 5.38 Vector Definitions for Equation 1.1 Through Equation 1.11
Vector Analog Quantities Description
V2 1/3 [3V2FIM]  3V2FIA Negative-sequence voltage
V0 1/3 [3V0FIM]  3V0FIA Zero-sequence voltage
I2 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
------
•


–• =
Z2FTH 1.25 Z2F 0.25
V
2
I
2
------
•


–• =