4.59
Date Code 20100129 Instruction Manual SEL-751A Relay
Protection and Logic Functions
Reclose Logic
programmable timer before using it in the preceding 79CLS and 79STL
settings for the SEL-751A(2) (see Figure 4.30). Note the built-in 2-cycle
qualification of the synchronism-check voltages shown in Figure 4.20.
EXAMPLE 4.6 Settings Example 2
Refer to subsection
Synchronism-Check Elements on page 4.33
. Also
refer to
Figure 4.32
and
Figure 4.33
.
If the synchronizing voltages across open circuit breaker 52/2 are
“slipping” with respect to one another, the Reclose Supervision Limit
Timer setting 79CLSD should be set greater than zero so there is time
for the slipping voltages to come into synchronism. For example:
79CLSD := 1.00 second
79CLS := 25A1
The status of synchronism-check element 25A1 is checked
continuously during the 60-cycle window. If the slipping voltages
come into synchronism while timer 79CLSD is timing, synchronism-
check element 25A1 asserts to logical 1 and reclosing proceeds.
In the above referenced subsection, note item 3 under
Synchronism-
Check Element Outputs on page 4.40
, Voltages VP and VS are
“Slipping.” Item 3 describes a last attempt for a synchronism-check
reclose before timer 79CLSD times out (or setting 79CLSD := 0.00
and only one check is made).
If E79 := 3 (which allows three automatic reclose attempts) and the
slipping voltages fail to come into synchronism while timer 79CLSD is
timing (resulting in a reclose supervision failure, causing RCSF to
assert for one processing interval), then the reclosing relay goes to
the Lockout State.
Reclose Logic
Note that input:
Reclosing Relay Open Interval Time-Out
in Figure 4.31 is the logic input that is qualified by SEL
OGIC control equation
setting 79CLS, and then propagated on to the close logic in Figure 4.30 to
automatically reclose a circuit breaker. The explanation that follows in this
reclosing relay subsection describes all the reclosing relay settings and logic
that eventually result in this open interval time-out logic input into
Figure 4.31. Other aspects of the reclosing relay are also explained. Up to four
(4) automatic reclosures (shots) are available.
The reclose enable setting, E79, has setting choices OFF, 1, 2, 3, and 4. Setting
E79 = OFF defeats the reclosing relay. Setting choices 1 through 4 are the
number of desired automatic reclosures (see Open Interval Timers on
page 4.63). Setting choices 1 through 4 also have the reclosing relay go to the
Lockout state upon reclose supervision failure (refer to Reclose Supervision
Logic on page 4.54).
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