R.2.3
Date Code 20111215 Reference Manual SEL-421 Relay
Auto-Reclosing and Synchronism Check
Auto-Reclosing
Reclaim Time Delay) timer has expired. You can only block the reclaim time
after a successful reclose cycle. Setting 79BRCT (Block Reclaim Timer)
prevents timing of reclaim timers SPRCD and 3PRCD.
Single-Pole Auto-Reclose (79CY1)
The auto-reclose logic is in a single-pole auto-reclose cycle for either circuit
breaker if the following conditions are satisfied:
➤ Single-pole trip occurs
➤ Condition(s) to initiate a single-pole auto-reclose cycle are
satisfied
➤ Circuit breaker(s) is in-service and ready to begin a single-pole
auto-reclose cycle (that is, reset)
Three-Pole Auto-Reclose (79CY3)
The auto-reclose logic is in a three-pole auto-reclose cycle for either circuit
breaker if the following conditions are satisfied:
➤ Three-pole trip occurs
➤ Condition(s) to initiate a three-pole auto-reclose cycle are
satisfied
➤ Circuit breaker(s) is in-service and ready to begin a three-pole
auto-reclose cycle (that is, reset)
Lockout (BK1LO, BK2LO)
The lockout state is the default state of any circuit breaker after power up.
Other conditions place the recloser in the LO state. The SEL-421 recloser has
a drive-to-lockout function that you can program for any external or internal
condition; use setting 79DTL. A circuit breaker can go to lockout by two
methods. If supervisory Relay Word bits SPnCLS or 3PnCLS do not assert
within the BKnCLSD time, or if the circuit breaker does not close within the
BKCFD time, then the circuit breaker enters the lockout state. The timer for
both supervisory Relay Word bits SPnCLS and 3PnCLS is setting BKnCLSD.
In applications using two circuit breakers, you can designate one circuit
breaker as the leader and the other circuit breaker as the follower. The relay
freezes the leader/follower decision during an auto-reclose cycle unless the
auto-reclose logic receives another initiation.
If the recloser receives another initiation, the logic reevaluates the leader and
follower circuit breakers to determine the number of circuit breakers in a
scheme (NBKn), the leader circuit breaker (LEADBKn), and the follower
circuit breaker (FOLBKn). This determination is based on the service status of
the circuit breakers. The logic considers a circuit breaker out of service if the
circuit breaker goes to lockout. The logic considers a circuit breaker to be in
service as soon as the circuit breaker closes and is no longer in lockout.
State Diagram
Figure 2.1 illustrates how the auto-reclose logic moves from one state to
another with respect to Circuit Breaker 1. (This diagram is identical for Circuit
Breaker 2; replace the 1 in the Relay Word bits with 2.) The Relay Word bits
that correspond to each state are shown (see Table 2.1). A solid path between
two states indicates that the logic can move in only one direction. Two broken
NOTE: The SEL-421 auto-reclose
function runs at once per power-
system cycle. To ensure that the logic
detects transient element state
changes that initiate closing, you
should extend the assertion time of
transient element states to 1 cycle.
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