Tips & News - November 2014

The Advantage “We have a lot of reclosers, fuses, and sectionalizing devices to help keep our line segments small. At the end of the day, we do it to reduce the number of customers that are affected by any one outage,” says Thorne. Wheredoes thisarrangementworkwell?Just abouteverywhere. Thorne explains, “it’s not necessarily a long or short feeder solution. We use this configuration on feeders that branch frequently. Our distribution system looks like a spider web. At every single intersection there is a split or fork and the line goes here and there. Those are the feeders that are candidates to have a lot of devices on them.” Alabama Power tries to limit the number of customers on each device to about 500, where it can. This is no small task, since the utility (headquartered in Birmingham, Alabama) provides electricity to 1.4 million customers. Decide Where Finding a good place to add a sectionalizer is often easy. Cheney explains how to do it: “If you look at the feeder map, you can see places that look like a good spot to stick a sectionalizer. Branching feeders make good locations but geography is also important. If there’s a river or impediments that a repairman would have to drive a long way to get around...that is also a good spot.” Like other utilities, Alabama Power also looks at the indices for its feeders. Every feeder is ranked, based on performance, and money is appropriately allocated. Outages Alabama Power experiences its share of outages. Many are caused by lightning, but the primary cause is animal outages. “Down here in the south, we have these things with four little legs and a bushy tail. It is amazing what a squirrel can tear up. And, we have enough animal related problems that ‘Possum’ is a valid code in our outage management system,” expounds Thorne. Single and Three-Phase Sectionalizers The utility has been using Hubbell Power Systems’ single-phase sectionalizers for the past 15 years. And it has just started installing Hubbell’s three-phase units as well. The utility has over 500 single-phase sectionalizers on its system. It only recently started installing Hubbell’s three-phase units but plans to add more. Cheney points out, “In the past, we used another vendor’s three- phase sectionalizers, but they quit making the 200 amp model. The only alternative they offer is a 400 amp sectionalizer. So, we went with Hubbell because the device does what we need it to do and we’ve had a good history with Hubbell. They are especially good when it comes to technical support.”

(Alabama Power has relatively high, short-circuit currents on its system. It is a densely populated area and the substations are closer together. The utility’s short-circuits currents are typically in the 2,000 to 3000 amp range.) Alabama Power typically uses three, single-phase sectionalizers on a three-phase circuit, but it depends on the situation. “Sometimes we need a three-phase device to avoid single phasing a customer. In that case, we use the Hubbell’s three- phase sectionalizer,” says Cheney. Most of Alabama Power’s large, commercial customers are served by a 2,000 to 2,500 amp padmount transformer. The bayonet fuses in those transformers will not coordinate with upstream line devices. So, the utility often uses a sectionalizer to help with coordination. Cheney adds, “we can put a fuse on the risers because it would have to be smaller than the bayonet fuses. We like to have our underground system protected or at least be able to disconnect it if there is a fault. Reclosers are expensive. And we can’t use fuses because of the size. So the only thing that’s left really is a sectionalizer.” According to Thorne, “the three-phase device is desirable from a price standpoint and it is an appealing addition for medium- sized pad mounted transformers for our industrial customers. When our engineers want to provide the customer some type of three-phase protection, Hubbell’s three-phase sectionalizer is significantly cheaper than the other options.” The utility also has problems with ferro-resonance, which can occurwhena three-phase load is servedbyaY-Delta transformer. If you lose one phase of the line, the neutral can shift on the Delta side. “It doesn’t happen a lot, but when it does, we don’t want to smoke our customer’s motors,” says Cheney. We have a lot of reclosers, fuses, and sectionalizing devices to help keep our line segments small. At the end of the day, we do it to reduce the number of customers that are affected by any one outage.

Cheney continues, “The three-phase sectionalizer is another tool we can use. It gives our engineers a little more flexibility.”

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