reclosing

Reclosing is an electrical protection technique used on electric power transmission and distribution systems. It involves automatically interrupting and then re-energizing a circuit after a fault, with the aim of restoring service quickly while isolating faults that are permanent. The scheme relies on protective relays and controllable devices called reclosers. When a fault causes an overcurrent or other abnormal condition, the protective system opens the circuit. After a short dead time, the recloser is commanded to close again. If the fault has cleared, the line returns to service; if the fault persists, the recloser will reopen and may lock out.

Reclosing schemes are usually multi-shot sequences. A rapid initial reclose is followed by longer delays and additional attempts, commonly three or four shots. If the fault persists after the final attempt, the circuit is locked out. Reclosing can be all-pole (three-phase) or single-pole on lines to limit stress when only one phase is faulty; however, many faults require simultaneous reclosing of all poles. Protection coordination with downstream devices such as sectionalizers is crucial to avoid unnecessary interruptions or unsafe conditions.

Impact and considerations: Reclosing reduces the duration of outages for transient faults caused by weather, lightning, or temporary contact, improving reliability. It can, however, re-energize a line into a persistent fault, risking equipment damage or safety hazards. Operators tailor timing and sequence to line impedance, weather, and the presence of distributed generation. Modern grids use adaptive reclosing strategies and coordinated protection to balance reliability, safety, and equipment life.