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4.11
Date Code 20171021
Instruction Manual
SEL-421 Relay
Front-Panel Operations
Target LEDs
The
COMM
LED illuminates, indicating that tripping resulted from a communica-
tions-assisted trip. The relay lights the
COMM
target when there is a relay tripping
condition and the Relay Word bit COMPRM (communications-assisted trip per-
mission) asserts.
The
SOTF
target LED indicates that the switch-onto-fault protection logic oper-
ated. 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 Z1P or Z1G distance elements
operated or if the high-speed Zone 1 elements operated.
The
ZONE 2
target illuminates if either the Z2P or Z2G distance elements
operated or if the high-speed Zone 2 elements operated and the similar ele-
ments in Zone 1 did not operate.
The
ZONE 3
target illuminates if either the Z3P or Z3G distance elements
operated or if the high-speed Zone 3 elements operated and the similar ele-
ments in Zone 1 and Zone 2 did not operate.
The
ZONE 4
target illuminates if either the Z4P 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 tar-
geting 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 illumi-
nates 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.
Table 4.3
TIME Target LED Trigger Elements—Factory Defaults
Mho
Quadrilateral
M2PT
Z2GT
M3PT
Z3GT
M4PT
Z4GT
M5PT
Z5GT
Summary of Contents for SEL-421-4
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