6.10
SEL-351A Relay Instruction Manual Date Code 20080213
Close and Reclose Logic
Reclose Supervision Logic
Other Setting Considerations for SEL-351A(1) and SEL-351A(2) Relays
Refer to Skip Shot and Stall Open Interval Timing Settings (79SKP and
79STL, respectively) on page 6.23.
SEL
OGIC control equation setting 79STL stalls open interval timing if it
asserts to logical 1. If setting 79STL is deasserted to logical 0, open interval
timing can continue.
The SEL-351A(1) Relay has no intentional open interval timing stall
condition (circuit breaker 52/1 closes first after a transmission line fault):
79STL = 0 (numeral 0)
The SEL-351A(2) Relay starts open interval timing after circuit breaker 52/1
at the remote end has reenergized the line. The SEL-351A(2) Relay has to see
Bus 2 hot, transmission line hot, and in synchronism across open circuit
breaker 52/2 for open interval timing to begin. Thus, SEL-351A(2) Relay
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)]
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-351A(2) Relay 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-351A(2) Relay 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-351A(2) Relay (see Figure 7.23 and Figure 7.24). Note
the built-in three- cycle qualification of the synchronism check voltages
shown in Figure 3.27.
Additional Settings
Example 2
Refer to subsection Synchronism Check Elements (Not in SEL-351A-1) on
page 3.36. 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.
where:
25A1 = selected Bus 2 phase voltage (VA, VB, or VC) is in
synchronism with monitored single-phase transmission
line voltage (channel VS) and both are hot
Courtesy of NationalSwitchgear.com
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