3.30
SEL-551 Relay Instruction Manual Date Code 20110408
Relay Elements and Logic
Reclosing Relay
Two open intervals are also set in the factory settings, resulting in last shot = 2.
Anytime 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 = 2):
79DLS = 79LO = logical 1
Thus, if local bit LB1 (reclose enable switch) is in the “disable reclosing”
position (LB1 = logical 0) or local bit LB3 (manual trip switch) is operated,
then the relay is driven to the Lockout State (by setting 79DTL) and
subsequently last shot (by setting 79DLS).
Additional Settings Example 1
The preceding drive-to-lockout factory settings example drives the relay to the
Lockout State immediately when the reclose enable switch (local bit LB1) is
put in the “reclosing disabled” position (Relay Word bit LB1 = logical 0):
79DTL = !LB1 + ... = NOT(LB1) + ... = NOT(logical 0) + ... = logical 1
To disable reclosing, but not drive the relay to the Lockout State until the relay
trips, make settings similar to the following:
79DTL = !LB1 * TRIP + ...
Additional Settings Example 2
To drive the relay to the Lockout State for fault current above a certain level
when tripping (e.g., level of phase instantaneous overcurrent element 50P3),
make settings similar to the following:
79DTL = TRIP * 50P3 + ...
Other Settings Considerations
If no special drive-to-lockout or drive-to-last shot conditions are desired, make
the following settings:
79DTL = 0 (numeral 0)
79DLS = 0 (numeral 0)
With settings 79DTL and 79DLS inoperative, the SEL-551 will still end up in
the Lockout State (and at last shot) if an entire automatic reclose sequence is
unsuccessful.
Overall, settings 79DTL or 79DLS are needed to take the SEL-551 to the
Lockout State (or to last shot) for immediate circumstances.
Skip Shot and Stall
Open Interval Timing
Settings (79SKP and
79STL, Respectively)
The skip shot setting 79SKP causes a reclose shot to be skipped. Thus, an
open interval time is skipped, and the next open interval time is used instead.
If 79SKP = logical 1 at the instant of successful reclose initiation (see
preceding discussion on settings 79RI and 79RIS), the relay increments the
shot counter to the next shot and then loads the open interval time
corresponding to the new shot (see Table 3. 6). If the new shot turns out to be
the “last shot,” no open interval timing takes place, and the relay goes to the
Lockout State if the circuit breaker is open (see preceding discussion on last
shot and shot counter).
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