U.6.38
SEL-421 Relay User’s Guide Date Code 20090715
Testing and Troubleshooting
Relay Self-Tests
c. You will see a RELAY ELEMENTS screen with SEARCH
highlighted at the bottom of the screen.
d. Press {ENT} to go to the
ELEMENT SEARCH submenu of
Figure 6.20.
e. Use the navigation keys to highlight
M and press {ENT} to
enter character in the text input field.
f. Enter the
B, C, and 2 characters in like manner.
g. Highlight
ACCEPT and press {ENT}.
The relay displays the LCD screen containing the
MBC2 element, as shown in Figure 6.30.
Figure 6.30 RELAY ELEMENTS LCD Screen Containing Element MBC2
Step 6. Set the magnitudes and angles of the test signals for a B-phase-
to-C-phase fault.
a. Connect the test sources (with power off) to the relay, as
in Figure 6.6.
This connection is a B-phase-to-C-phase fault where
I
A
≈ 0 and I
B
= –I
C
.
b. Adjust the voltage sources to provide the following test
voltages: V
A
= 67 V ∠0°, V
B
= 46.8 V ∠–150°, and
V
C
= 46.8 V ∠150° .
c. Set the current source for I
B
= 0.0 A ∠–174° .
Step 7. Apply the sources to confirm operation of MBC2.
a. Apply the source test current by slowly increasing the
magnitude of I
B.
b. Observe the RELAY ELEMENT LCD screen.
Relay Word bit MBC2 asserts when |I
B
| ≥ 2.5 A,
indicating that the relay impedance calculation is less
than the Z2P reach setting.
Relay Self-Tests
The SEL-421 continuously runs many self-tests to detect out-of-tolerance
conditions. These tests run at the same time as relay protection and
automation logic, but do not degrade SEL-421 performance.
Status Warning and
Status Failure
The relay reports out-of-tolerance conditions as a status warning or a status
failure. For conditions that do not compromise relay protection, yet are
beyond expected limits, the relay issues a status warning and continues to
operate. A severe out-of-tolerance condition causes the relay to declare a
status failure and enter a protection-disabled state. During a protection-
PRESS to search
RELAY ELEMENTS
SEARCH
ROW 8 ROW 9
* =0 * =0
MCA2 =0 MCA4 =0
MBC2 =0 MBC4 =0
MAB2 =0 MAB4 =0
* =0 * =0
MCA1 =0 MCA3 =0
MBC1 =0 MBC3 =0
MAB1 =0 MAB3 =0
Courtesy of NationalSwitchgear.com
To Next Page
Loading...
