6-12 Close and Reclose Logic Date Code 20001006
SEL-351 Instruction Manual
Note: 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-351(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-351(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-351(2) Relay (see Figure 7.25 and Figure 7.26). Note the built-in
3-cycle qualification of the synchronism check voltages shown in Figure 3.24.
Additional Settings Example 2
Refer to subsection Synchronism Check Elements in Section 3: Overcurrent, Voltage,
Synchronism Check, Frequency, and Power Elements. Also refer to Figures 6.3 and 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, 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).
RECLOSING RELAY
Note that input:
Reclosing Relay Open Interval Time-Out
in Figure 6.2 is the logic input that is qualified by SELOGIC Control Equation setting 79CLS, and
then propagated on to the close logic in Figure 6.1 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 6.2. Other
aspects of the reclosing relay are also explained. Up to four (4) automatic reclosures (shots) are
available.
Courtesy of NationalSwitchgear.com
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