Recloser

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.

At two multiples of the rated current, the recloser's rapid trip curve can cause a trip (off circuit) in as little as 1.5 cycles (or 30 milliseconds). During those 1.5 cycles, other separate circuits can see voltage dips or blinks until the affected circuit opens to stop the fault current. Automatically closing the breaker after it has tripped and stayed open for a brief amount of time, usually after 1 to 5 seconds, is a standard procedure.^[5]

Reclosers are often used as a key component in a smart grid, as they are effectively computer controlled switchgear which can be remotely operated and interrogated using supervisory control and data acquisition (SCADA) or other communications. Interrogation and remote operation capabilities allow utilities to aggregate data about their network performance, and develop automation schemes for power restoration. Automation schemes can either be distributed (executed at the remote recloser level) or centralized (close and open commands issued by a central utility control room to be executed by remotely controlled ACRs).