3.19
Date Code 20110408 Instruction Manual SEL-551 Relay
Relay Elements and Logic
Trip Logic
With setting TDURD = 9.000 cycles, once the TRIP Relay Word bit is
asserted via the OPEN command or setting TR, it remains asserted at logical
1 for a minimum of nine cycles.
Unlatch Trip
In SELOGIC control equation setting ULTR = !(51P1 + 51G1):
➤ Both time-overcurrent element pickups 51P1P and 51G1P must
be deasserted before the trip logic unlatches and the TRIP
Relay Word bit deasserts to logical 0.
ULTR = !(51P1 + 51G1) = NOT(51P1 + 51G1) = NOT(51P1) * NOT(51G1)
Additional Settings
Examples
The factory setting for SELOGIC control equation setting ULTR is a current-
based trip unlatch condition. A circuit breaker status unlatch trip condition can
be programmed as shown in the following examples.
Unlatch Trip With 52a Circuit Breaker Auxiliary Contact
A 52a circuit breaker auxiliary contact is wired to optoisolated input IN1.
52A = IN1 (SELOGIC Control Equation Breaker Status Setting—see Close
Logic on page 3.20)
ULTR = !IN1
Input IN1 has to be de-energized (52a circuit breaker auxiliary contact has to be
open) before the trip logic unlatches and the TRIP Relay Word bit deasserts to
logical 0.
ULTR = !IN1 = NOT(IN1)
Unlatch Trip With 52b Circuit Breaker Auxiliary Contact
A 52b circuit breaker auxiliary contact is wired to optoisolated input IN1.
52A = !IN1 (SELOGIC Control Equation Breaker Status setting—see Close
Logic)
ULTR = IN1
Input IN1 must be energized (52b circuit breaker auxiliary contact has to be
closed) before the trip logic unlatches and the TRIP Relay Word bit deasserts
to logical 0.
Program an Output
Contact for Tripping
In the factory settings, the resultant of the trip logic in Figure 3.13 is routed to
output contact OUT1 with the following SEL
OGIC control equation:
OUT1 = TRIP
See Output Contacts on page 3.39 for more information on programming
output contacts.
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