Autorecloser
Encyclopedia
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.
s or fuse
s which will turn off power in the event of a short circuit
. This presents a major problem dealing with transient events. For instance, a tree branch that is blown off a tree during a windstorm and lands on the line may cause a short circuit that could cause damage. However, the fault will quickly clear itself as the branch falls to the ground. If the only protection system is the breakers at the distribution centres, large areas of the grid would be blacked out while the repair crew resets the breakers.
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 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 the single recloser, long before the feeder station would notice a problem. A normal breaker could also be used for this role, but because they are distributed geographically throughout the grid, as opposed to being centralized at feeder stations, resetting a breaker might take considerable time. For this reason, 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 opens again.
The control system for a recloser allows a selected number of attempts to restore service after adjustable time delays. 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 branches 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.
equipped with a tripping mechanism triggered by a counter or a timer. A sectionalizer does not interrupt fault current. It observes fault current and circuit interruption by the autorecloser. If the autorecloser cycles and the fault persists, the sectionalizer will open its branch circuit during the open period of the autorecloser, thereby isolating the faulty section of the circuit.
Electric power distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...
, a recloser, or autorecloser, is a circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
equipped with a mechanism that can automatically close the breaker after it has been opened due to a fault
Fault (power engineering)
In an electric power system, a fault is any abnormal flow of electric current. For example, a short circuit is a fault in which current flow bypasses the normal load. An open-circuit fault occurs if a circuit is interrupted by some failure. In three-phase systems, a fault may involve one or more...
. 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.
Description
In order to prevent damage, each station along the network is protected with circuit breakerCircuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
s or fuse
Fuse
The word fuse has several meanings:* Fuse , a device used in electrical systems to protect against excessive current....
s which will turn off power in the event of a short circuit
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
. This presents a major problem dealing with transient events. For instance, a tree branch that is blown off a tree during a windstorm and lands on the line may cause a short circuit that could cause damage. However, the fault will quickly clear itself as the branch falls to the ground. If the only protection system is the breakers at the distribution centres, large areas of the grid would be blacked out while the repair crew resets the breakers.
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 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 the single recloser, long before the feeder station would notice a problem. A normal breaker could also be used for this role, but because they are distributed geographically throughout the grid, as opposed to being centralized at feeder stations, resetting a breaker might take considerable time. For this reason, 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 opens again.
The control system for a recloser allows a selected number of attempts to restore service after adjustable time delays. 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 branches 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
Availability
In telecommunications and reliability theory, the term availability has the following meanings:* The degree to which a system, subsystem, or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time...
of supply.
Autoreclosers are made in single-phase and three-phase
Three-phase electric power
Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads...
versions, and use either oil, vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
, or SF6
Sulfur hexafluoride
Sulfur hexafluoride is an inorganic, colorless, odorless, and non-flammable greenhouse gas. has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule. Typical for a nonpolar gas, it is poorly soluble in water but soluble in...
interrupters. Controls for the reclosers range from the original electromechanical systems to digital electronics with metering
Electricity meter
An electricity meter or energy meter is a device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device....
and SCADA
SCADA
SCADA generally refers to industrial control systems : computer systems that monitor and control industrial, infrastructure, or facility-based processes, as described below:...
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.
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.Sectionalizer
Reclosers may cooperate with down-stream protective devices called "sectionalizers", which present disconnectors or cutoutsCutout (electric power distribution)
In electrical distribution, a fuse cutout or cut-out fuse is a combination of a fuse and a switch, used in primary overhead feeder lines and taps to protect distribution transformers from current surges and overloads. An overcurrent caused by a fault in the transformer or customer circuit will...
equipped with a tripping mechanism triggered by a counter or a timer. A sectionalizer does not interrupt fault current. It observes fault current and circuit interruption by the autorecloser. If the autorecloser cycles and the fault persists, the sectionalizer will open its branch circuit during the open period of the autorecloser, thereby isolating the faulty section of the circuit.