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6.37
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
ments determines the priority in which these elements operate to provide the
ground directional element. Only one specific directional element operates at any
one time. Directional element classification is as follows:
➤
Q—Negative-sequence voltage-polarized directional element
➤
V—Zero-sequence voltage-polarized directional element
➤
I—Zero-sequence current-polarized directional element
Set ORDER to QV. The first listed directional element choice, Q, is the first pri-
ority directional element to provide directional control for the ground-distance
elements and residual ground directional overcurrent elements. If Q is not opera-
ble, the second listed directional element choice, V, provides directional control
for the ground-distance elements and residual ground directional overcurrent ele-
ments. A polarizing quantity was not available for choice I, so I is not selected for
this particular application example.
ORDER :=
QV
.
Ground Directional Element Priority (combine Q, V, I)
SEL
OGIC
control equation E32IV must assert to logical 1 to enable V or I for
directional control of the ground-distance elements and residual ground direc-
tional overcurrent elements. Set E32IV to logical 1.
E32IV :=
1
.
Zero-Sequence Voltage and Current Enable (SEL
OGIC
Equation)
Pole-Open Detection
The setting EPO offers two options for deciding what conditions signify an open
pole, as listed in
Select the second option because a 52A contact is available. The relay uses both
open-phase detection and status information from the circuit breaker to make the
most secure decision.
EPO :=
52
.
Pole-Open Detection (52, V)
Pole-Open Time Delay on Dropout
SPOD is the time delay on dropout after the Relay Word bit SPO deasserts. This
time delay allows power system transients to settle after the open pole recloses,
thereby stabilizing the ground-distance elements corresponding to that phase. If a
three-pole open condition (3PO) asserts, SPOD resets immediately.
SPOD :=
0.500
.
Single-Pole Open Dropout Delay (0.000–60 cycles)
Table 6.11
Options for Enabling Pole-Open Logic
Option
Description
EPO := V
The logic declares a single-pole open if the corresponding phase undervolt-
age element asserts and the open-phase detection logic declares the pole is
open. Select this option only if you use line-side potential transformers for
relaying purposes. A typical setting for the 27PO, pole-open undervoltage
threshold, is 60 percent of the nominal line-to-neutral voltage.
Do not select this option when shunt reactors are applied, because the volt-
age slowly decays after the circuit breaker opens. With this option selected,
the relay can incorrectly declare LOP during a pole-open condition if there
is charging current that exceeds the pole-open current threshold.
EPO := 52
The logic declares a single-pole open if the corresponding 52A contact
(52AA1, for example) from the circuit breaker deasserts and the open-phase
detection logic declares that the pole is open.
Summary of Contents for SEL-421-4
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