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 50Pn phase overcurrent elements, 50Qn
negative-sequence overcurrent elements, and the 50Gn 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 Circuit Breaker
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).
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