Why is the placement and coordination of reclosers critical in minimizing customer interruption minutes (CIM) during transient faults?

Customer Interruption Minutes (CIM) is a key metric that quantifies the average duration of power outages experienced by customers. Transient faults, like those caused by lightning strikes or momentary contact with trees, are temporary and often self-clearing. Reclosers are automatic switching devices designed to quickly interrupt the power flow during a fault and then automatically restore it after a short time delay. Proper placement of reclosers is crucial to sectionalize the distribution system. This means strategically locating them to isolate faults to the smallest possible section of the feeder. If a recloser is placed too far downstream, a fault will interrupt power to a larger number of customers. Coordination refers to setting the operating characteristics (time-current curves) of multiple reclosers, fuses, and circuit breakers in a sequence. The recloser closest to the fault should operate first. If it successfully clears the fault (which is common for transient faults), the upstream devices remain closed, and only the customers downstream of the recloser experience a momentary interruption. If the first recloser fails to clear the fault (indicating a permanent fault), the next upstream recloser or protective device will operate after a longer delay. Poor coordination can lead to multiple devices tripping unnecessarily, causing a widespread outage and significantly increasing the CIM. Effective placement and coordination of reclosers allows for quickly clearing transient faults while minimizing the number of customers affected and the duration of their interruption.