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6.24
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
Equation 6.8
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)
Use Level 1 high-set instantaneous phase overcurrent element for SOTF
protection.
E50P :=
1
.
Phase Instantaneous/Definite-Time Overcurrent Elements (N, 1–4)
This application does not require residual ground overcurrent protection.
E50G :=
N
.
Residual Ground Instantaneous/Definite-Time Overcurrent Ele-
ments (N, 1–4)
This application does not require negative-sequence overcurrent protection.
E50Q :=
N
.
Negative-Sequence Instantaneous/Definite-Time Overcurrent Ele-
ments (N, 1–4)
Use inverse-time overcurrent protection to provide backup protection for high-
resistance ground faults. The 51S1 element provides backup protection for unbal-
anced faults if both the communications-assisted and step distance protection fail
to operate.
E51S :=
1
.
Selectable Inverse-Time Overcurrent Element (N, 1–3)
Set E32 to AUTO or AUTO2 and the relay automatically calculates the settings
corresponding to the ground directional element (32G).
E32 :=
AUTO2
.
Directional Control (Y, AUTO, AUTO2)
SIR
2
Z
1S
•
0.8
Z
1L
•
--------------------------
=
2 • 4.45
0.8 • 3.98
------------------------------
=
2.76, SIR 5
=
Summary of Contents for SEL-421-4
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