Sel 751A - Determination of Number of Reclosures (Last Shot); Figure 4.35 Reclosing Sequence from Reset to Lockout with Example Settings; Observe Shot Counter Operation; Reset Timer

4.64
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Reclose Logic
If open interval 1 time setting, 79OI1, is set to zero (79OI1 := 0.00 seconds),
no open interval timing takes place, and the reclosing relay is defeated.
The open interval timers time consecutively; they do not have the same
beginning time reference point. For example, with settings 79OI1 := 0.50 , and
79OI2 := 10.00, open interval 1 time setting, 79OI1, times first. If subsequent
first reclosure is not successful, then open interval 2 time setting, 79OI2, starts
timing. If the subsequent second reclosure is not successful, the relay goes to
the Lockout State. See the example time line in Figure 4.35.
Figure 4.35 Reclosing Sequence From Reset to Lockout With Example Settings
SELOGIC control equation setting 79STL (stall open interval timing) can be
set to control open interval timing [see Skip Shot and Stall Open Interval
Timing Settings (79SKP and 79STL, Respectively) on page 4.69].
Determination of Number of Reclosures (Last Shot)
The number of reclosures is equal to the number of open interval time settings
that precede the first open interval time setting set equal to zero. The “last
shot” value is also equal to the number of reclosures.
In the above example settings, two set open interval times precede open
interval 3 time, which is set to zero (79OI3 = 0.00):
79OI1 := 0.50
79OI2 := 10.00
79OI3 := 0.00
For this example:
Number of reclosures (last shot) = 2 = the number of set open interval
times that precede the first open interval set to zero.
Observe Shot Counter Operation
Observe the reclosing relay shot counter operation, especially during testing,
using ASCII command TARGET (e.g., TARGET Command (Display Relay
Word Bit Status) on page 7.41 for detail).
Reset Timer
The reset timer qualifies circuit breaker closure before taking the relay to the
Reset State from the Reclose Cycle State or the Lockout State. Circuit breaker
status is determined by the SEL
OGIC control equation setting 52A. (See Trip/
Close Logic on page 4.50 for more discussion on SEL
OGIC control equation
setting 52A.
Open Interval Time-out
Shot
Counter
0
52A
79OI1 = 0.5
Reset State
Trip Close Trip Close Trip
Reclose Cycle State Lockout State
(79OI3 = 0)
79OI2 = 10.0
(Last Shot = 2)
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