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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
analog quantities are listed in
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
Table 5.37
Reference Table for
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
------
•
–
•
=
Summary of Contents for SEL-421-4
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