U.5.32
SEL-421/SEL-421-1 Relay User’s Guide Date Code 20020501
Front-Panel Operations
Operation and Target LEDs
The COMM LED illuminates, indicating that tripping resulted from a
communications-assisted trip. The relay lights the COMM target when there is
a relay tripping condition and the Relay Word bit COMPRM
(communications-assisted trip permission) asserts.
The SOTF target LED indicates that the switch-onto-fault protection logic
operated. The relay illuminates the SOTF target when there is a relay tripping
condition and the Relay Word bit SOTFT (switch-onto-fault trip) asserts.
Zone Activated
The zone activated area target indicators are the ZONE 1, ZONE 2, ZONE 3,
and ZONE 4 LEDs. These targets illuminate when the corresponding zone
distance elements pick up and there is a relay tripping condition. In factory
default programming, the lowest zone LED has priority; only the LED
corresponding to the closest protection zone latches for distance element
pickups.
The ZONE 1 target illuminates if either the M1P or Z1G distance
elements operated or if the high-speed Zone 1 elements operated.
The ZONE 2 target illuminates if either the M2P or Z2G distance
elements operated or if the high-speed Zone 2 elements operated and the
similar elements in Zone 1 did not operate.
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 Relay
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.
Ta bl e 5. 6 T IM E Tar get L ED Tr i gg er El em e nt s– Fac t or y De fau lt s
Mho Quadrilateral
M2PT Z2GT
M3PT Z3GT
M4PT Z4GT
M5PT Z5GT
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