Reclaim Timer Setting
A number of factors influence the choice of the reclaim timer, such as:
− Supply continuity - long reclaim times can result in unnecessary lockout for transient
faults.
− Fault incidence and past experience - short reclaim times may be required where
there is a high incidence of lightning strikes to prevent unnecessary lockout for
transient faults.
− Spring charging time - for high-speed autoreclose the reclaim time may be set longer
than the spring charging time to ensure there is sufficient energy in the circuit breaker
to perform a trip-close-trip cycle. For delayed autoreclose there is no need to set the
reclaim time longer than the spring charging time as the dead time can be extended
by an extra CB healthy check window time if there is insufficient energy in the CB. If
there is insufficient energy after the check window time has elapsed the relay will
lockout.
− Switchgear maintenance - excessive operation resulting from short reclaim times can
mean shorter maintenance periods. A minimum reclaim time of >5 s may be needed
to allow the CB time to recover after a trip and close operation before it can perform
another trip-close-trip cycle. This time will depend on the duty (rating) of the CB.
− The reclaim time must be long enough to allow any time-delayed protection initiating
autoreclose to operate. Failure to do so would result in premature resetting of the
autoreclose scheme and re-enabling of instantaneous protection.
− If this condition arose, a permanent fault would effectively look like a number of
transient faults, resulting in continuous autoreclose operations unless additional
measures were taken to overcome this, such as excessive fault frequency lockout
protection.
− A sensitive earth fault protection is usually applied to detect high resistance earth
faults.
Usually, a long trip delay time is set, typically 10 - 15 s. This longer time may be taken
into consideration, if autoreclose is started by an earth fault protection, and when
deciding on a reclaim time, if the reclaim time is not blocked by a SEF protection start
signal. Sensitive earth faults, for example, a broken overhead conductor in contact
with dry ground or a wood fence, is rarely transient and presents great danger to
persons and animals. It is therefore common practice to block autoreclose by
operation of sensitive earth fault protection and lockout the circuit breaker.
− Where motor-wound spring closed circuit breakers are used, the reclaim time must be
at least as long as the spring winding time for high-speed autoreclose to ensure that
the breaker can perform a trip-close-trip cycle.
− A typical 11/33kV reclaim time is 3 - 10 seconds; this prevents unnecessary lockout
during thunderstorms. However, reclaim times up to 60 - 180 seconds maybe used.
