6.10
SEL-311C Relay Instruction Manual Date Code 20060320
Close and Reclose Logic
Reclose Supervision Logic
open interval timing to begin. Thus, SEL-311C(2) open interval timing is
stalled when the transmission line voltage and Bus 2 voltage are not in
synchronism across open circuit breaker 52/2:
79STL = !25A1 [=NOT(25A1)]
Note that a transient synchronism check condition across open circuit breaker
52/2 could possibly occur if circuit breaker 52/1 recloses into a fault on one
phase of the transmission line. The other two unfaulted phases would be
briefly energized until circuit breaker 52/1 is tripped again. If channel VS of
the SEL-311C(2) is connected to one of these briefly energized phases,
synchronism check element 25A1 could momentarily assert to logical 1.
So that this possible momentary assertion of synchronism check element
25A1 does not cause any inadvertent reclose of circuit breaker 52/2, make
sure the open interval timers in the SEL-311C(2) are set with some
appreciable time greater than the momentary energization time of the faulted
transmission line. Or, run the synchronism check element 25A1 through a
programmable timer before using it in the preceding 79CLS and 79STL
settings for the SEL-311C(2) (see Figure 7.24 and Figure 7.25). Note the
built-in three-cycle qualification of the synchronism check voltages shown in
Figure 3.30.
Additional
Settings Example 2
Refer to subsection Synchronism Check Elements on page 3.44. Also refer to
Figure 6.3 and Figure 6.4.
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 = 60.00 cycles
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 Synchronism Check Elements, note item 3
under Synchronism Check Element Outputs on page 3.52, Voltages V
P
and V
S
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).
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