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6.28
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
Zone 1 Reactance
Zone 1 quadrilateral ground-distance reactance reach must meet the same
requirement as that for Zone 1 mho phase-distance protection; the reach setting
should be no greater than 80 percent of the line.
XG1 = 0.8 • Z
1L1
= 3.18
XG1 :=
3.18
.
Zone 1 Reactance (OFF, 0.05–64
secondary)
Zone 1 Resistance
Find RG1 (Zone1 resistance) from the per-unit reach
m
of the Zone 1 reactance.
Use
, which is
Equation 3
in
Appendix A—Quadrilateral Reactive
Reach Versus Resistive Reach Setting Guideline
from the paper
Digital Commu-
nications for Power System Protection: Security, Availability, and Speed
. You can
find a copy of this paper on the SEL website at selinc.com.
Equation 6.9
XG1 is set at 80 percent of the transmission line (i.e., m = 0.8 per-unit); the posi-
tive-sequence reactance of the overhead transmission line X
1L1
is 3.977
sec-
ondary (from the rectangular form of Z
1L1
in
Equation 6.10
Figure 6.5
Quadrilateral Ground-Distance Element Reactive Reach Setting
X
XG
R
where:
m = per-unit reach of XG1
R = RG1, the Zone 1 resistance
X
1L1
= positive-sequence transmission line reactance
m
1
R
X
1L1
• 20
------------------------
–
=
Z
1L1
3.98
87.6
=
R
1L1
jX
1L1
+
=
0.167 j3.977
+
=
Содержание SEL-421-4
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