Distribution single-phase tripping and reclosing: Overcoming obstacles with programmable recloser controls

Ever since the first ground-fault detection device was incorporated into a fault interrupting mechanism, limitations have existed as to how much sustained load unbalance could be tolerated for a given three-phase distribution feeder. All single-phase fault interruption will introduce some incremental unbalance if load is dropped. Therefore, projected peak load levels beyond the location of fault interrupting and sectionalizing devices have always been determining factors as to whether the protection device would isolate all phases or only the faulted ones. For example, fuses, being independent phase-interrupting devices, can only be used at locations where the load they interrupt will not cause unbalance above the pickup level of upline ground-fault detection equipment. Single-phase reclosers and sectionalizers must also be applied with similar consideration. Traditionally, if high load levels will be interrupted, three-phase circuit reclosers with gang-operated interrupters are used.