Minimizing Outages with Interrupting Devices

In an industry driven by the size of performance indices, minimizing the size of an outage is vital. Alabama Power does this by adding interrupting devices to the lines. "Just like everyone else, we're driven by SAIDI, SAIFI, MAIDI and MAIFI," said Robert Cheney, Team Keader of Alabama Power Test Lab. "We're taking a hard look at our system and figuring out what we can to do improve those numbers." 

Alabama Power's strategy to preventing outages includes fuses, reclosers and sectionalizers. Line devices and protection schemes can usually handle three or four, time-coordinated devices on a feeder, while still maintaining proper separation between tipping curves. Using a combination of both sectionalizers and reclosers allows you to add more devices to the line. 

• THE ALTERNATING APPROACH: Alabama Power is now utilizing an alternating approach to reclosers and sectionalizers. Their sectionalizers are not programmed to open during the third open interval. This allows two opportunities for the line to clear temporary faults before the sectionalizer operates. They utilize a lot of reclosers, fuses and sectionalized devices to keep line segments small. This helps to reduce the number of customers affected by any one power outage. Alabama Power tries to limit the number of customers on each device to 500. This is no small task. 
• DECIDE WHERE: Finding a good place for a sectionalizer is often easy. When looking at a feeder map make sure you take into account geography. Take into consideration geography when choosing a location. The more difficult it is for a repairman to get to that location the more likely that a sectionalizer is needed in that area. 
• THREE-PHASE SECTIONALIZERS: Alabama Power typically uses three, single-phase sectionalizers on a three-phase circuit. Most of their large, commercial customers are served by a 2,000 to 2,500 amp pad mount transformer. The bayonet fuses in those transformers will not coordinate with upstream line devices. Often a sectionalizer is needed to help with coordination. The three-phase device is desirable from a price standpoint and it is an appealing addition for medium-sized pad mounter transformers for industrial customers.  

Alabama Power has been successfully utilizing sectionalizers for years. This process has allowed the engineers to be more flexible in the field. How does your utility handle coordinated devices? Leave a comment below.