4.69
Date Code 20100129 Instruction Manual SEL-751A Relay
Protection and Logic Functions
Reclose Logic
EXAMPLE 4.10 Additional Settings Example
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 50P3P), make settings similar to the following:
79DTL := TRIP AND 50P3P OR ...
Additionally, if the reclosing relay should go to the Lockout State for
an underfrequency trip, make settings similar to the following:
79DTL := TRIP AND 81D1T OR ...
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 relay still goes to the
Lockout State (and to last shot) if an entire automatic reclose sequence is
unsuccessful.
Overall, settings 79DTL or 79DLS are needed to take the relay 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 4.28). If the new shot is the “last
shot,” no open interval timing takes place, and the relay goes to the Lockout
State if the circuit breaker is open (see Lockout State on page 4.61).
After successful reclose initiation, open interval timing does not start until
allowed by the stall open interval timing setting 79STL. If 79STL = logical 1,
open interval timing is stalled. If 79STL = logical 0, open interval timing can
proceed.
If an open interval time has not yet started timing (79STL = logical 1 still), the
79SKP setting is still processed. In such conditions (open interval timing has
not yet started timing), if 79SKP = logical 1, the relay increments the shot
counter to the next shot and then loads the open interval time corresponding to
the new shot (see Table 4.28). 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 Lockout State on page 4.61).
If the relay is in the middle of timing on an open interval and 79STL changes
state to 79STL = logical 1, open interval timing stops where it is. If 79STL
changes state back to 79STL = logical 0, open interval timing resumes where
it left off. Use the OPTMN Relay Word bit to monitor open interval timing
(see Monitoring Open Interval and Reset Timing on page 4.65).
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