4.58
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Reclose Supervision Logic
SEL-751A(1) Relay
Before allowing circuit breaker 52/1 to be reclosed after an open
interval time-out, the SEL-751A(1) checks that Bus 1 voltage is hot and
the transmission line voltage is dead. This requires reclose
supervision settings:
79CLSD := 0.00 seconds (only one check)
79CLS := 59VP AND 27S
SEL-751A(2) Relay
The SEL-751A(2) checks that Bus 2 voltage is hot, the transmission
line voltage is hot, and in synchronism after the reclosing relay open
interval times out, before allowing circuit breaker 52/2 to be reclosed.
This requires reclose supervision settings:
79CLSD := 0.00 seconds (only one check)
79CLS := 25A1
Other Setting Considerations for SEL-751A(1) and SEL-751A(2) Relays
Refer to Skip Shot and Stall Open Interval Timing Settings (79SKP and
79STL, Respectively) on page 4.69.
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-751A(1) has no intentional open interval timing
stall condition (circuit breaker 52/1 closes first after a transmission line fault):
79STL := 0
The SEL-751A(2) starts open interval timing after circuit breaker 52/1 at the
remote end has reenergized the line. The SEL-751A(2) 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-751A(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 := 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-751A(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-751A(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
where:
59VP = Bus 1 is hot
27S1 = monitored single-phase transmission line voltage
(channel VS) is dead
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
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