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| Auto Circuit Recloser |
It is a self-contained device with the
necessary circuit intelligence to sense overcurrents, to time and
interrupt the overcurrents and to reclose automatically to
re-energize the line.
If the faults should be “permanent”
the recloser will lock open after a preset number of operations
(usually 3 or 4) and thus isolate the faulted section from the main
part of the system.
Most faults on overhead distribution
systems – perhaps as high as 70 – 80% are likely to be temporary
in nature & last only a few cycles to few a seconds at the most.
ACR with their trip & reclose capability, eliminate prolonged
outages on distribution systems due to temporary faults or transient
overcurrent conditions.
Reclosers can be used anywhere on a
system where the recloser ratings are adequate for the system
requirements. Logical locations are:
1. In substations as the primary feeder
protective device.
2. On the lines at a distance from a
substation to sectionalize long feeders and thus prevent outages of
the entire feeder when a permanent fault occurs near the end of the
feeder.
3. On the taps of main feeders
(lateral), to protect the main feeder from interruptions and outages
due to faults on the taps.
4. Reclosers are available as
padmounted units to provide simple, direct connections to underground
cable systems.
Major factors must be considered for
proper application of ACRs:
1. System Voltage
The recloser must have a voltage
rating equal to or greater than the system voltage.
2. Maximum fault current available at
the point of recloser location.
The recloser interrupting rating must
be equal to or greater than the maximum available fault current.
3. Maximum Load Current
The maximum continuous current rating
of the recloser must be equal to or greater than the maximum maximum
load current anticipated for the circuit.
4. Minimum fault current within the
zone to be protected by the recloser.
The minimum fault current that might
occur at the end of the line section to be protected must be checked
to determine that the recloser will sense & interrupt this
current.
5. Coordination with other protective
devices on both source & load sides of the recloser.
Proper selection of time delays &
sequences is vital to ensure that any momentary interruption or
longer outage due to faults is restricted to the smallest possible
section of the system.
6. Ground Fault Sensing
The ground fault settings ( minimum
trip & timing) must be coordinated with the phase trip settings
of the downline single phase devices like single phase reclosers &
fuses.
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