Sel 551 - Page 59

3.21
Date Code 20110408 Instruction Manual SEL-551 Relay
Relay Elements and Logic
Close Logic
Unlatch Close
If the CLOSE Relay Word bit is asserted at logical 1, it stays asserted at
logical 1 until one of the following occurs:
➤ The unlatch close condition asserts (ULCL = logical 1),
➤ The circuit breaker closes (52A = logical 1),
➤ The reclose initiation condition (79RI) makes a rising edge
(logical 0 to logical 1) transition,
➤ Or the Close Failure Timer times out (Relay Word bit CF = 1).
The Close Failure Timer is inoperative if setting CFD = 0. Then, the CLOSE
Relay Word bit can be deasserted to logical 0 only if one of the following
occurs:
➤ The unlatch close condition asserts (ULCL = logical 1),
➤ The circuit breaker closes (52A = logical 1),
➤ Or the reclose initiation condition (79RI) makes a rising edge
(logical 0 to logical 1) transition.
Factory Settings
Example
The factory settings for the close/reclose logic SELOGIC control equation
settings are:
CL = LB4
ULCL = TRIP
52A = IN1
The factory setting for the Close Failure Timer setting is:
CFD = 60.000 cycles
See the setting sheets in Section 4: Setting the Relay for setting ranges.
Set Close
SELOGIC control equation setting CL is set with local bit LB4. Local bit LB4
closes directly (operates as a manual close switch via the front panel). See
Local Control Switches on page 3.5 and Section 6: Front-Panel Interface for
more information on local control.
Unlatch Close
SELOGIC control equation setting ULCL is set with the TRIP Relay Word bit.
This prevents the CLOSE Relay Word bit from being asserted any time the
TRIP Relay Word bit is asserted (TRIP takes priority). See Trip Logic on
page 3.17.
SEL
OGIC control equation setting 52A is set with optoisolated input IN1. Input
IN1 is connected to a 52a circuit breaker auxiliary contact. Setting 52A
operates on 52a circuit breaker auxiliary contact logic. When a closed circuit
breaker condition is detected, the CLOSE Relay Word bit is deasserted to
logical 0. Setting 52A can handle a 52a or 52b circuit breaker auxiliary contact
connected to an optoisolated input (see Optoisolated Inputs on page 3.3 for
more 52A setting examples).
With setting CFD = 60.000 cycles, once the CLOSE Relay Word bit is
asserted, it can remain asserted at logical 1 for no longer than a maximum of
60 cycles.