3.21
Date Code 20171021
Instruction Manual
SEL-421 Relay
Testing
Checking Relay Operation
The relay measures phase-distance element maximum reach when the faulted
phase-to-phase current lags the faulted phase-to-phase voltage by the distance
element maximum torque angle. In the SEL-421, the phase-distance element
maximum torque angle is setting Z1ANG. Current I
BC
should lag voltage V
BC
by
Z1ANG.
In this example, Z1ANG is 84.0 degrees. From
, the angle of I
B
is
the angle of I
TEST
, and the angle of I
C
is 180 degrees from the angle of I
TEST
. The
test source current for I
B
is the following:
Equation 3.13
And the test source current for I
C
is the following:
Equation 3.14
Checking the MBC2 Portion of the Z2P Phase-Distance Element
The following procedure describes how to test the B-Phase to C-Phase distance
element MBC2. Although this test refers directly to the Zone 2 phase-distance
element, you can apply this procedure to any other forward-reaching phase-to-
phase distance element zone.
Step 1. Configure the relay.
Perform the procedure listed under
Sequence Directional Element (Phase Faults) on page 3.13
.
Step 2. Set test values in the relay.
Perform the procedure listed under
Sequence Directional Element (Phase Faults) on page 3.13
.
Step 3. Set the phase-distance element reach.
a. Select the
Phase Distance
button of the QuickSet
Settings
tree
view.
You will see the
Phase Distance Elements
dialog box similar to
b. Confirm the settings of
E2IP
at
2
,
Z1MP
at
6.24
and
Z2MP
at
9.36
.
I
B
2.5
90
–
Z1ANG
–
A
=
2.5
90
–
84
–
A
=
2.5
174
A
–
=
I
C
I
B
2.5
174
A
–
2.5 6
A
=
–
=
–
=
Figure 3.18
Phase-Distance Elements Settings: QuickSet
NOTE:
As you perform this test,
other protection elements can assert.
This causes the relay to assert other
targets and possibly close control
outputs. Be sure to isolate the relay
from the power system to avoid
unexpected system effects.
Summary of Contents for SEL-421-4
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