What is an automatic circuit recloser?

Answer 1

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.

They 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 reclose 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.

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 40 amperes at 2400 volts up to 1200 amperes at 35000 volts.

Answer 2

High-voltage overhead lines are subject to transient faults during storms. ' Transient faults' are temporary line-to-line or line-to-earth short-circuits caused by, for example, conductors being struck by branches. A transient fault will cause the line's protective circuit breaker to disconnect the circuit. An autorecloser is a motorised accessory which will recharge a circuit breaker's mechanism and cause it to reclose following a transient fault. If the fault has cleared, then the circuit breaker will remain closed and the line will remain energised. If the fault remains, then the circuit breaker will reopen.

Reclosers can be set to operate a number of times before permanently locking the circuit breaker open. Often, reclosers operate in conjuction with several 'sectionalisers'. These are non-load-breaking switches distributed along the length of a line, that will automatically while the line becomes disconnected. They can be arranged so that the far end of the line is disconnected permanently during the first disconnection, then a closer section of line is disconnected during the second disconnection, until the fault is finally cleared.