Sel SEL-421 - Auto-Reclosing; Logical States; Start (79 STRT); Reset (BK1 RS, BK2 RS)

R.2.2
SEL-421 Relay Reference Manual Date Code 20111215
Auto-Reclosing and Synchronism Check
Auto-Reclosing
The SEL-421 synchronism-check function uses single-phase input voltages
V
S1
, V
S2
(source voltages), and reference V
P
(polarizing voltage) to provide
synchronism check for one or two circuit breakers. The relay determines when
V
S1
and V
S2
are within programmable voltage magnitudes and slip frequency
windows compared to V
P
. In addition, the synchronism-check function can
use settable circuit breaker closing times and the measured slip frequencies to
compensate the angle difference calculation between V
S1
and V
P
(plus V
S2
and V
P
). The relay checks this angle difference calculation in a programmable
synchronism angle window.
Auto-Reclosing
Logical States
The auto-reclose logic for either circuit breaker can be in one of five states
(see Figure 2.1):
➤ Start (common to both circuit breakers) (79STRT)
➤ Reset per circuit breaker (BK1RS, BK2RS)
➤ Single-pole auto-reclose cycle (common to both circuit
breakers) (79CY1)
➤ Three-pole auto-reclose cycle (common to both circuit
breakers) (79CY3)
➤ Lockout, per circuit breaker (BK1LO, BK2LO)
Start (79STRT)
The auto-reclose logic is in the Start state for both circuit breakers during the
following conditions:
➤ Power up
➤ Restart
➤ Any relay settings change
The SEL-421 stores the previous reclosing state for Relay Word bits 79CY1,
79CY3, BK1LO, BK2LO, BK1RS, and BK2RS when a restart or any relay
settings change occurs.
At power up the recloser logic goes from the start state to the lockout state.
For a restart or a settings change, the recloser logic enters the start state, then
goes to lockout if the circuit breakers were open before the restart or settings
change. If the circuit breakers were previously closed, then the recloser logic
proceeds through the 3PMRCD (Manual Close Reclaim Time Delay) time and
then goes to the ready state.
Reset (BK1RS, BK2RS)
The auto-reclose logic is in the reset or ready state for either circuit breaker
when the circuit breaker is ready to begin an auto-reclose cycle. There are
three reset state timers. After a successful reclose cycle, the relay goes to the
reset state after reclaim times SPRCD (Single-Pole Reclaim Time Delay) for
single-pole automatic and 3PRCD (Three-Pole Reclaim Time Delay) for
three-pole automatic reclosing. If the recloser has been in a lockout condition,
the Ready or Reset state cannot occur until the 3PMRCD (Manual Close