R.2.11
Date Code 20111215 Reference Manual SEL-421 Relay
Auto-Reclosing and Synchronism Check
Two-Circuit-Breaker Auto-Reclosing
Single-Pole Mode
Figure 2.12 and Figure 2.13 show the two circuit breaker single-pole auto-
reclose cycle 79CY1 when E79 := Y and E79 := Y1, respectively. The cycle
starts when Relay Word bit SPARC asserts. The recloser freezes calculation of
the number of breakers, the leader circuit breaker, and the follower circuit
breaker. Depending on the calculation, the recloser asserts the appropriate
Relay Word bits NBK0, NBK1, NBK2, LEADBK0, LEADBK1, LEADBK2,
FOLBK0, FOLBK1, and FOLBK2.
The recloser checks for an SPO (Single-Pole Open) condition for either the
leader or follower, and waits as long as 10 cycles for the circuit breakers to
open. If the leader or follower shows a single-pole open inside the 10-cycle
window, the recloser proceeds to timing SPOID (Single-Pole Open Interval
Delay). The recloser goes to lockout if the circuit breakers fail to open (no
close attempts follow). If an evolving fault results in a three-pole trip
condition that asserts 3PARC, then the recloser exits the 79CY1 cycle and
goes to the three-pole cycle 79CY3. When E79 := Y1, a Single-Pole Open
Interval Supervision Condition (SPOISC) must be satisfied before the recloser
can proceed to timing SPOID. If the supervisory condition is not met within
the duration of timer SPOISD (Single-Pole Open Interval Supervision Delay),
the recloser goes to lockout.
After single-pole open interval time SPOID expires, the recloser closes the
leader if the single-pole open condition is still in effect and supervisory
condition SPnCLS (Single-Pole BKn Reclose Supervision) is satisfied within
the duration of timer BKnCLSD (BKn Reclose Supervision Delay). If the
leader circuit breaker has more than one pole open at the end of the SPOID
time, the recloser sends the leader to lockout BKnLO.
At the leader close command, the recloser starts timer BKCFD (Breaker Close
Failure Delay). If the leader fails to close, the recloser sends the leader to
lockout after timer BKCFD expires. If the leader closes within the BKCFD
time, the recloser goes to SPRCD (Single-Pole Reclaim Time Delay) reclaim
timing if NBK1 is asserted, or prepares to close the follower circuit breaker if
NBK2 is asserted.
To close the follower circuit breaker, the recloser checks for two active circuit
breakers in the scheme. If NBK2 is asserted, the recloser checks for a single-
pole open on the follower and starts timer TBBKD (Time Between Breakers
For ARC). If multiple poles of the follower circuit breaker are open, the
recloser sends the follower to lockout BKnLO. When TBBKD expires, the
recloser closes the follower breaker if FBKCEN (Follower Breaker Closing
Enable) is asserted and supervisory condition SPnCLS is satisfied within the
duration of timer BKnCLSD. At the follower close command, the recloser
starts timer BKCFD (Breaker Close Failure Delay). If the follower fails to
close, the recloser sends the follower to lockout after timer BKCFD expires. If
the leader circuit breaker is not in lockout, the recloser begins timing SPRCD
reclaim time for the leader.
If the follower breaker closes successfully, the recloser starts the SPRCD
(Single-Pole Reclaim Time Delay) timer if 79BRCT (Block Reclaim Timer) is
not asserted.
SPRCD Reclaim Timing
The recloser determines subsequent state transitions during reclaim timing
according to the status of Relay Word bit SPLSHT (Single-Pole Reclose Last
Shot). When SPLSHT is asserted, the recloser forces all subsequent relay trips
to three-pole only mode.
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