4.68
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Reclose Logic
If the following setting is made:
79RI := 0 (numeral 0)
reclosing will never take place (reclosing is never initiated). The reclosing
relay is effectively inoperative.
If the following setting is made:
79RIS := 0 (numeral 0)
reclosing will never take place (the reclosing relay goes directly to the lockout
state any time reclosing is initiated). The reclosing relay is effectively
inoperative.
Drive-to-Lockout and
Drive-to-Last Shot
Settings (79DTL and
79DLS, Respectively)
When 79DTL = logical 1, the reclosing relay goes to the Lockout State (Relay
Word bit 79LO = logical 1), and the front-panel LO (Lockout) LED
illuminates.
79DTL has a 1 second dropout time. This keeps the drive-to-lockout condition
up 1 second after 79DTL has reverted back to 79DTL = logical 0. This is
useful for situations where both of the following are true:
➤ Any of the trip and drive-to-lockout conditions are “pulsed”
conditions (e.g., the OPEN command Relay Word bit, OC,
asserts for only 1/4 cycle—refer to Factory Settings Example
on page 4.68).
➤ Reclose initiation is by the breaker contact opening (e.g., 79RI
:= NOT 52A—refer to Additional Settings Example on
page 4.67).
Then the drive-to-lockout condition overlaps reclose initiation and the
SEL-751A stays in lockout after the breaker trips open.
When 79DLS = logical 1, the reclosing relay goes to the last shot, if the shot
counter is not at a shot value greater than or equal to the calculated last shot
(see Reclosing Relay Shot Counter on page 4.66).
EXAMPLE 4.9 Factory Settings Example
The drive-to-lockout factory setting is:
79DTL := OC OR SV04T
Relay Word bit OC asserts for execution of the OPEN command. See
the Note in the Lockout State discussion, following Table 4.26 .
Relay Word bit SV04T asserts for execution of the open command
from front panel push button (see Table 8.4 on page 8.15 for more
detail).
The drive-to-last shot factory setting is:
79DLS := 79LO
One open interval is also set in the factory settings, resulting in last
shot = 1. Any time the relay is in the lockout state (Relay Word bit
79LO = logical 1), the relay is driven to last shot (if the shot counter is
not already at a shot value greater than or equal to shot = 1):
79DLS := 79LO = logical 1
Thus, the relay is driven to the Lockout State (by setting 79DTL) and,
subsequently, last shot (by setting 79DLS).
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