In electric power distribution, a recloser, or autorecloser, is a circuit breaker equipped with a mechanism that can automatically close the breaker after it has been opened due to a fault. Reclosers are used on overhead distribution systems to detect and interrupt momentary faults. Since many short-circuits on overhead lines clear themselves, a recloser improves service continuity by automatically restoring power to the line after a momentary fault.
Video Recloser
Description
In order to prevent damage, each station along the network is protected with circuit breakers or fuses which will turn off power in the event of a short circuit. This presents a major problem when dealing with transient events. For instance, a tree limb blown off a tree during a windstorm that lands on the power line may cause a short circuit that could cause damage. However, the fault could quickly clear itself as the limb falls to the ground. If the only protection system is provided by breakers at distribution centres, large areas of the grid could be blacked out while repair crews reset the breakers. Reclosers are programmed to automate the reset process and allow a more granular approach to service restoration.
Reclosers address this problem by further dividing up the network into smaller sections. For instance, the city grid example above might be equipped with reclosers at every branch point on the network. Reclosers, because of their upstream position in the network, handle much less power than the breakers at the feeder stations, and therefore can be set to trip at much lower power levels. This means that a single event on the grid will cut off only the section handled by a single recloser, long before the feeder station would notice a problem. The recloser's scope is much more limited.
A breaker could also be used for this, but because this would distribute the equipment geographically throughout the grid, as opposed to centralizing them at feeder stations, resetting breakers might take considerable time due to geography. So reclosers are used to automatically re-connect after a brief interval. There is a strong likelihood that the fault will be gone when the power is restored. If the fault is still present, the recloser re-opens.
The control system for a recloser allows a selected number of attempts to restore service after an adjustable time delay. For example a recloser may have 2 or 3 "fast" reclose operations with a few seconds delay, then a longer delay and one reclose; if the last attempt is not successful, the recloser will lock out and require human intervention to reset.
If the fault is a permanent fault (downed wires, tree limbs lying on the wires, etc.) the autorecloser will exhaust its pre-programmed attempts to re-energize the line and remain tripped off until manually commanded to try again. About 80-90% of faults on overhead power lines are transient and can be cured by autoreclosing. The result is increased availability of supply.
Autoreclosers are made in single-phase and three-phase versions, and use either oil, vacuum, or SF6 interrupters. Controls for the reclosers range from the original electromechanical systems to digital electronics with metering and SCADA functions. The ratings of reclosers run from 2.4-38 kV for load currents from 10-1200 A and fault currents from 1-16 kA.
On a 3 phase circuit a recloser is more beneficial than three separate fuse cutouts. For example on a wye to delta conversion if cutouts are used on the wye side, and only 1 out of 3 of the cutout fuses open, some customers on the delta side would have a low voltage condition, due to voltage transfer through the transformer windings. Low voltage can cause severe damage to electronic equipment. But if a recloser were used, all three phases will open, eliminating the problem.
Maps Recloser
Autoreclosers in action
Residential customers in areas fed by affected overhead power lines can occasionally see the effects of an autorecloser in action. If the fault affects the customer's own distribution circuit, they may see one or several brief, complete outages followed by either normal operation (as the autorecloser succeeds in restoring power after a transient fault has cleared) or a complete outage of service (as the autorecloser exhausts its retries). If the fault is on an adjacent circuit, the customer may see several brief "dips" (sags) in voltage as the heavy fault current flows into the adjacent circuit and is interrupted one or more times. A typical manifestation would be the dip, or intermittent black-out, of domestic lighting during an electrical storm. Autorecloser action may result in electronic devices losing time settings, losing data in volatile memory, halting, restarting, or suffering damage due to power interruption. Owners of such equipment may need to protect electronic devices against the consequences of power interruptions and also power surges.
Sectionalizer
Reclosers may cooperate with down-stream protective devices called sectionalizers, usually a disconnector or cutouts equipped with a tripping mechanism triggered by a counter or a timer. A sectionalizer is generally not rated to interrupt fault current and is therefore cheaper than a recloser. Each sectionalizer detects and counts fault current interruptions by the recloser (or circuit breaker). After a pre-determined number of interruptions, the sectionalizer will open, thereby isolating the faulty section of the circuit, allowing the recloser to restore supply to the other non-fault sections.
See also
- List of California wildfires
- October 2017 Northern California wildfires
- Pacific Gas and Electric
- San Diego Gas and Electric
- Witch Fire
- Black Saturday bushfires
References
Source of the article : Wikipedia
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