U.5.39
Date Code 20090715 User’s Guide SEL-421 Relay
Front-Panel Operations
Operation and Target LEDs
The ZONE 3 target illuminates if either the M3P or Z3G distance elements
operated or if the high-speed Zone 3 elements operated and the similar
elements in Zone 1 and Zone 2 did not operate.
The ZONE 4 target illuminates if either the M4P or Z4G distance elements
operated and the similar elements in Zone 1, Zone 2, and Zone 3 did not
operate.
Phase(s) or Ground
The phase(s) or ground targets illuminate according to the SEL-421 special
targeting logic. This logic accurately classifies which phase, phases, and/or
ground were involved in a trip event.
The PHASE A target LED lights for faults on the power system A-phase.
Single-phase-to-ground faults from A-phase to ground illuminate both the
PHASE A and GROUND targets. A phase-to-phase fault between A-phase and
B-phase illuminates the PHASE A target and the PHASE B target.
The relay displays faults involving other phase combinations similarly. If the
phase-to-phase fault includes ground, the relay also lights the GROUND target.
The relay lights the PHASE A, PHASE B, and PHASE C target LEDS for a three-
phase fault.
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 elements, 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
programmed lockout conditions exist.
The 79 CYCLE target illuminates when the relay the relay is in the auto-reclose
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 R.2.50 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 R.1.121 for complete details.
Courtesy of NationalSwitchgear.com
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