R.2.15
Date Code 20111215 Reference Manual SEL-421 Relay
Auto-Reclosing and Synchronism Check
Two-Circuit-Breaker Auto-Reclosing
beginning of the three-pole auto-reclose cycle state 79CY3. The recloser
proceeds through the 79CY3 state and exits this state as described in Three-
Pole Mode on page R.2.12.
Three-Pole Priority
If a single-pole auto-reclose cycle is in progress (79CY1) and the relay
receives an initiation for three-pole reclosing (3PRI), the recloser immediately
starts a three-pole auto-reclose cycle (79CY3).
Active Circuit
Breakers
The following three Relay Word bits describe when Circuit Breaker BK1 and
Circuit Breaker BK2 are active for the auto-reclose logic:
➤ NBK0, No Breaker Active in Reclose Scheme
➤ NBK1, One Breaker Active in Reclose Scheme
➤ NBK2, Two Breakers Active in Reclose Scheme
Leader and Follower
Circuit Breakers
One circuit breaker is the leader and the other is the follower for circuit
breaker-and-a-half and ring-bus arrangements. Figure 2.2 illustrates a multiple
circuit breaker arrangement. The leader recloses first. If the leader recloses
successfully, the follower also typically recloses.
Figure 2.2 Multiple Circuit Breaker Arrangement
Choose Circuit Breaker BK1 as the leader and Circuit Breaker BK2 as the
follower. If Circuit Breaker BK1 is out of service (for maintenance, for
example), the SEL-421 can automatically make Circuit Breaker BK2 the
leader.
The relay freezes the leader, follower, and number of active circuit breaker
designations during an auto-reclose cycle. If the logic receives another reclose
initiation, the relay reevaluates the leader, follower, and number of active
circuit breaker designations. The logic considers a circuit breaker out of
service if the circuit breaker goes to lockout, and declares a circuit breaker to
be in service as soon as the circuit breaker closes and is no longer in lockout.
Leader Logic
Relay settings SLBK1 (Leader Breaker = Breaker 1) and SLBK2 (Leader
Breaker = Breaker 2) SEL
OGIC control equations determine the criteria for
relay selection of the active leader. Set SLBK1 := 1 to select Circuit Breaker 1
as the leader; set SLBK2 := 1 to select Circuit Breaker 2 as the leader. SLBK1
has priority over SLBK2; if you set both settings to 1 or both to 0, Circuit
Breaker 1 is the leader.
Bus 1
(Leader) (Follower)
Line
Bus 2
BK2
BK1
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