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4.12
SEL-421 Relay
Instruction Manual
Date Code 20171021
Front-Panel Operations
Target LEDs
Instantaneous and Time-Delayed Overcurrent
The
50
target LED indicates that an instantaneous overcurrent element picked up.
These elements are the nondirectional 50P
n
phase overcurrent elements, 50Q
n
negative-sequence overcurrent elements, and the 50G
n
ground overcurrent ele-
ments, where
n
is the overcurrent level;
n
= 1, 2, 3, and 4.
The
51
target LED illuminates if a time-overcurrent element has timed out. The
relay lights this LED if any of the selectable operating quantity inverse-time
overcurrent elements 51S1T, 51S2T, and 51S3T assert.
Recloser Status
The
79 RESET
,
79 LOCKOUT
, and
79 CYCLE
target LEDs show the operating status of
the SEL-421 reclosing function.
The
79 RESET
LED indicates that the relay recloser is in the reset or ready-to-
reclose state for Circuit Breaker 1 (Relay Word bit BK1RS is asserted).
The
79 LOCKOUT
target illuminates when the relay has completed the reclose
attempts unsuccessfully (a drive-to-lockout condition), or when other pro-
grammed lockout conditions exist.
The
79 CYCLE
target illuminates when the relay the relay is in the autoreclose
cycle state for Circuit Breaker 1.
Miscellaneous Status
The
25 SYNCH
,
BKR CLOSE
,
BKR FAIL
,
OSB
, and
LOP
target LEDs illuminate in the
SEL-421 for miscellaneous status conditions.
The
25 SYNCH
LED illuminates when the relay detects that the Circuit Breaker 1
voltages are within Synchronism Angle 1 (Relay Word bit 25A1BK1 is asserted).
See
Synchronism Check on page 5.158
for complete details.
The
BKR CLOSE
LED illuminates when the relay detects a breaker close command
for Circuit Breaker 1 (Relay Word bit BK1CL is asserted).
The
BKR FAIL
LED illuminates when the relay detects a breaker failure trip for
Circuit Breaker 1 (Relay Word bit BFTRIP1 is asserted). See
Failure Trip Logic on page 5.154
for complete details.
The
OSB
LED illuminates when the relay detects an out-of-step condition (Relay
Word bit OSB is asserted). See
Out-of-Step Logic (Conventional) on page 5.50
for complete details.
The
LOP
LED illuminates when the relay detects a loss-of-potential condition
(Relay Word bit LOP is asserted). See
Loss-of-Potential Logic on page 5.28
for
complete details.
Synchrophasor Status
The
PMCU OK
target LED illuminates when the relay is enabled for synchrophasor
measurement (Relay Word bits TSOK and PMDOK are asserted).
Summary of Contents for SEL-421-4
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