3.22 Automatic Reclose 79AR
3.22.1 Overview
To maintain the integrity of the overall electrical transmission system, the device is installed on the
transmission system to isolate faulted segments during system disturbances. Faults caused by
lightning, wind, or tree branches could be transient in nature and may disappear once the circuit is
de-energized. According to statistics, 80%~90% of the faults on overhead lines are the transient
faults. Auto-reclosing systems are installed to restore the faulted section of the transmission
system once the fault is extinguished (providing it is a transient fault). For certain transmission
systems, auto-recloser is used to improve system stability by restoring critical transmission paths
as soon as possible.
When the auto-reclosing command is issued, the reclaim timer starts. If the circuit breaker does
not trip again, the auto-recloser resets at the end of the reclaim time. If another protection operates
during the reclaim time delay, this relay either proceeds to the next shot in the programmed
auto-reclosing cycle, or it lockouts if all programmed reclose attempts have been made. The
reclaim time should be set long enough to allow this relay to operate when the circuit breaker is
automatically closed onto a fault.
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