Reclosers are switching equipment used in transmission lines. A recloser can sense an overcurrent condition by itself and isolate the system. It does not need an external relay to operate it. When the overcurrent condition is cleared, it closes automatically in a pre-determined sequence.Reclosers are useful in distribution lines, where some of the overcurrent conditions are temporary in nature and clear quickly. They ensure that the system is normalized quickly.
After isolating a system, the recloser closes again after a preset time to see if the fault has been cleared. If the fault persists, the recloser trips again. It closes again for a few more times to see if the fault has cleared. Then it locks the system and permanently isolates it. The recloser then may need to be reset.
Like circuit breakers, reclosers consist of an interrupting mechanism with an insulating medium for arc extinction. They also contain coils for opening and closing, besides sensing transformers.
The tripping coils of reclosers are powered by the fault current which flows through the system. Unlike circuit breakers, where the closing coil is powered by an auxiliary supply, the reclosers are powered by a transformer which is located on the source side.
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