Autorecloser

From Wikipedia, the free encyclopedia

In electric power distribution, an autorecloser is a circuit breaker equipped with a mechanism that can automatically close the breaker after it has been opened due to a fault.[1] [2]

Autoreclosers are used in coordinated protection schemes for overhead line power distribution circuits. These circuits are prone to transitory faults such as nearby lightning strikes, wind-borne debris, squirrels climbing insulators, and the like. With a conventional circuit breaker or fuse, a transient fault would open the breaker or blow the fuse, disabling the line until a technician could manually close the circuit breaker or replace the blown fuse. But an autorecloser will make several pre-programmed attempts to re-energize the line. If the transient fault has cleared, the autorecloser's circuit breaker will remain closed and normal operation of the power line will resume. If the fault is some sort of 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. 90% of faults on overhead power lines are transient and can be cured by autoreclosing. [3] The result is increased availability of supply.

Reclosers work with similar down-stream protective devices called "sectionalizers" [4] A sectionalizer does not interrupt fault current. The sectionalizer 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.

Autoreclosers are made in single-phase and three-phase versions, and use either oil or vacuum 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 2400V - 38kV for load currents from 10A - 1200A and fault currents from 1000A - 16kA.

[edit] 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.

[edit] References

  1. ^ Richard c. Dorf (ed.) The Electrical Engineering Handbook, CRC Press, Boca Raton, 1993, ISBN 0-8493-0185-8, pg. 1319
  2. ^ Edwin Bernard Kurtz (ed), The Lineman's and Cableman's Handbook' 9th edition, McGraw Hill, New York 1997, ISBN 0-07-036011-1, pages 18-8 through 18-15
  3. ^ B. M. Weedy, Electric Power Systems Second Edition, John Wiley and Sons, London, 1972, ISBN 0471924458 page 26
  4. ^ Kurtz, "Lineman's and Cableman's Handbook" pg. 18-12.

[edit] External links