In electric power distribution, automatic circuit reclosers (ACRs) are a class of switchgear designed for use on overhead electricity distribution networks to detect and interrupt transient faults. Also known as reclosers or autoreclosers, ACRs are essentially rated circuit breakers with integrated current and voltage sensors and a protection relay, optimized for use as a protection asset. Commercial ACRs are governed by the IEC 62271-111/IEEE Std C37.60 and IEC 62271-200 standards.[1][2] The three major classes of operating maximum voltage are 15.5 kV, 27 kV and 38 kV.
For overhead electric power distribution networks, up to 80% of faults are transient, such as lightning strike, surges or foreign objects coming into contact with exposed distribution lines. Consequently, these transient faults can be resolved by a simple reclose operation.[3] Reclosers are designed to handle a brief open-close duty cycle, where electrical engineers can optionally configure the number and timing of attempted close operations prior to transitioning to a lockout stage.[4] The number of reclose attempts is limited to a maximum of four by recloser Standards noted above.
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Reclosers were invented in the mid 1900s in the USA with the earliest reclosers introduced by Kyle Corporation in the early 1940s.[10] Reclosers were originally oil filled hydraulic devices with rudimentary mechanical protection relaying capabilities. Modern automatic circuit reclosers are significantly more advanced than the original hydraulic units. The advent of semiconductor based electronic protective relays in the 1980s resulted in increased recloser sophistication, allowing for differing responses to the various cases of abnormal operation or fault on an electric power distribution network. The high voltage insulation and interrupting device in modern reclosers typically consist of solid dielectric insulation with vacuum interrupters for current interruption and arc quenching.[11][12]
To prevent electric power distribution network damage, each station along the network is protected with circuit breakers or fuse cutouts which will turn off power in the event of a short circuit. Using these protection solutions present a major problem when dealing with restoring power immediately following transient events, due to the fact that repair crews would need to manually reset the circuit breakers or replace fuses cutouts.
Traditional reclosers were designed simply to automate the action of a line crew visiting a remote distribution site to close a tripped circuit breaker and attempt to restore power. With the advanced protection functionality of modern reclosers, these devices are used in a multitude of additional applications
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.[17] A sectionalizer is generally not rated to interrupt fault current however it often has a larger Basic Insulation Level, allowing some sectionalizers to be used as a point of isolation. 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.[18] Some modern recloser controllers can be configured to have reclosers operate in sectionalizer mode. This is used in applications where protection grading margins are too small to provide effective protection co-ordination between electrical assets.
Fire risk is an innate risk of an overhead distribution network. Regardless of the choice of distribution protection switchgear, the fire risk is always higher with overhead conductors than with underground reticulation.[13]
Disconnects refer to a disconnector, a disconnect switch or an isolator switch is used to ensure that an electrical circuit is completely de-energized for service or maintenance. Found in electrical distribution and industrial application, these switches are crucial as machinery must be disconnected from the source of energy for adjustment or repair. To allow isolation of an apparatus such as circuit breakers, transformers, and transmission lines for maintenance, high-voltage isolation switches are used in electrical substations. The disconnector is usually not intended for normal control of the circuit, but only for safety isolation. Disconnectors can be operated either manually or automatically. Graybar has a variety of disconnects available for your electrical distribution systems. Categories include heavy-duty disconnects, general duty, double-throw disconnects, and air conditioner disconnects. Graybar also has many disconnect accessories to ensure your distribution system operates effectively. 2ff7e9595c
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