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 Equation 3.9, 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 Step 1 in Checking the Negative-
Sequence Directional Element (Phase Faults) on page 3.13.
Step 2. Set test values in the relay.
Perform the procedure listed under Step 2 in Checking the Negative-
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
Figure 3.18.
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 174A–=
I
C
I
B
2.5 174A–2.5 6A=–=–=
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.
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