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6.5
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Applications Examples
230 kV Overhead Distribution Line Example
The fault locator uses the values you enter for Z1MAG, Z1ANG, Z0MAG,
Z0ANG, and LL.
Relay Configuration
You can select from zero to five phase zones of mho phase (E21P), mho ground
(E21MG), and quadrilateral ground (E21XG) distance protection. You can inde-
pendently select the number of zones per type of distance protection. Select only
the number of zones needed. For this application example, use two zones of mho
phase and ground-distance protection.
E21P :=
2
.
Mho Phase-Distance Zones (N, 1–5)
E21MG :=
2
.
Mho Ground-Distance Zones (N, 1–5)
E21XG :=
N
.
Quadrilateral Ground-Distance Zones (N, 1–5)
Now enable the other logic you will need for this application example.
You do not need CVT transient detection if the SIR (Source Impedance Ratio) is
less than five. SIR is equal to the ratio of the local source impedance to the relay
reach. Calculate the ratio based on the Zone 1 reach because you do not want
Zone 1 distance protection to overreach during an external fault.
Equation 6.3
ECVT :=
N
.
CVT Transient Detection (Y, N)
NOTE:
The SEL-421-4 does not
provide series-compensated line
protection logic.
The transmission line is not series compensated.
ESERCMP :=
N
.
Series-Compensated Line Logic (Y, N)
You can select a common time delay or an independent time delay per zone for
phase and ground-distance protection. If you choose independent timing, evolv-
ing faults (such as those changing from single phase to multiphase) cause the
timer to reset and result in additional delay. Select common time delay for this
application.
ECDTD :=
Y
.
Distance Element Common Time Delay (Y, N)
The SOTF logic permits tripping by specified protection elements for a settable
time after the circuit breaker closes.
ESOTF :=
Y
.
Switch-Onto-Fault (Y, N)
Do not enable the Out-of-Step logic for this application example.
EOOS : =
N
.
Out-of-Step (Y, N)
Do not enable the load-encroachment logic, as the minimum apparent load
impedance is outside the mho phase-distance characteristics.
ELOAD :=
N
.
Load Encroachment (Y, N)
SIR
Z
1S
0.8
Z
1L
•
--------------------------
=
2.5
0.8 1.95
•
-------------------------------
=
1.603 SIR 5
=
Summary of Contents for SEL-421-4
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