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
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
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
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
Содержание 421
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