3.19
Date Code 20171021 Instruction Manual SEL-421 Relay
Testing
Checking Relay Operation
Step 7. Use Equation 3.5 to determine the applied current angle (I
TEST
):
Step 8. Apply a test current to confirm operation of R32Q and F32Q.
a. Connect a single current test source as shown in Figure 3.5.
b. Apply an A-Phase voltage of V
A
= 18.0 180° V secondary.
c. Set the current source for I
A
= 0.0 96° A.
d. Slowly increase the magnitude of I
A
to apply the source test
current.
e. Observe the
RELAY ELEMENT LCD screen.
Relay Word bit R32Q asserts when |I
A
| = 0.4 A, indicating that
the relay negative-sequence current is greater than the 50RP
pickup threshold.
R32Q deasserts when |I
A
| = 4.5 A, indicating that the relay
negative-sequence calculation Z2c is now less than the Z2
reverse threshold Z2R (see Forward Threshold on page 5.43 and
Reverse Threshold on page 5.44).
f. Continue to increase the current source while you observe the
RELAY ELEMENT LCD screen.
Relay Word bit F32Q asserts when |I
A
| = 4.62 A, indicating that
the relay negative-sequence calculation Z2c is less than the Z2
forward threshold Z2F.
Distance Elements
Apply voltages and currents to the relay analog inputs that simulate fault and load
conditions to test distance elements. The relay supervises distance elements so
that these elements operate under the appropriate conditions. Be sure to satisfy all
the element supervisory conditions before testing a relay element. For supervi-
sory conditions for a particular element, see Mho Ground-Distance Elements on
page 5.72.
Phase-to-Phase Distance Element MBC2
The SEL-421 contains mho phase-distance elements among the many protection
elements in the relay. The relay has phase-distance elements to detect phase-to-
phase faults, phase-to-phase-to-ground faults, and three-phase faults. The
SEL-421 has five independent zones of mho phase-distance protection; each zone
consists of phase-to-phase elements that the relay combines to produce a particu-
lar zone output.
For example, the OR combination of MAB2, MBC2, and MCA2 produces the
Z2P Zone 2 mho phase element. For more information on the mho phase ele-
ments and other distance elements, see Section 5: Protection Functions and
Section 6: Protection Applications Examples.
Test Current and Voltage for a Phase-to-Phase Fault
To find the test current for a phase-to-phase fault, consider Equation 3.9 for a
B-Phase to C-Phase fault:
Equation 3.9
I
TEST
3I
2
3V
2
Z1ANG 180 84 96=–=–==
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