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TUB: Power system can withstand cold

Posted on Tuesday, January 7, 2014 at 1:45 pm

Water lines more at risk during extremely frigid weather


kelly lapczynski


With temperatures dropping to zero in some places before a gradual warm-up the rest of the week, the Tullahoma Utilities Board says it was ready to weather the Arctic cold wave that moved across the region Monday and Tuesday.

“The TUB (electric) system is designed to be fully redundant with two delivery points from TVA,” said Brian Coate, electric and fiber department manager.  “Tullahoma is built out to more than twice the capacity it needs.”

Substations on Washington Street and Spring Creek Road provide that redundancy.

“TUB can serve the entire city out of either substation.  If we lose one, roughly two-thirds of the city will automatically roll over to the other substation,” Coate said.

In fact, it’s more likely that TUB vehicles rather than substations will be affected by cold weather during service calls. Substation failures are more likely when the weather gets hot.

“If you could keep a transformer at absolute zero, (AKA the theoretical temperature at which substances possess no thermal energy, equal to minus 459.67°F) you could push almost infinite power through it,” said Coate.  “The enemy of our system is heat.  It’s more of a problem in the summer.”

On Monday, when the daytime high hovered around 12 degrees, the system was running on only 64 megawatts of its 200-megawatt capacity.  The all-time peak power usage record of 73.5 megawatts was set in the summer, on Aug. 16, 2006.

TUB crews work Monday to repair a water main on Wilson Avenue.  Water lines and home water pipes are more susceptible to freezing temperatures than electric lines, according to TUB water department manager Scott Young.      — Staff Photo by Kelly Lapczynski

TUB crews work Monday to repair a water main on Wilson Avenue. Water lines and home water pipes are more susceptible to freezing temperatures than electric lines, according to TUB water department manager Scott Young.
— Staff Photo by Kelly Lapczynski

Though metal wires contract in the cold, tightening power lines, Coate says that’s not much of a concern in Tullahoma.  “We’re pretty good about right-sizing.”  Rather, he says, “Our guys get nervous when it’s 32 degrees and rainy.  That’s when ice becomes a concern.”

During the ice storm of 1998 there was only one delivery point, but Coate says that had nothing to do with the resultant power outage.  The cause of that outage was not losing substation power, but rather losing power lines to the weight of heavy ice formations.

Once a power line is down, the circuit is tripped and power cannot be restored to that unit until the wire is back in place.

“The lines are designed to carry the weight of a quarter-inch of ice,” said Coate.  “But any more than a quarter-inch begins to break poles and cross arms.  A half-inch of ice weighs several hundred pounds.”

And when one pole breaks, others can fall like dominos.


Water system more at risk

Barring an unusual accumulation of ice, the cold weather has more of an impact on TUB’s water system than it does on the electric system, said Coate.  Water department manager Scott Young confirms.

Young says the water system has already seen two breaks in the 6-inch cast-iron water mains as a result of cold weather this year: one on Ovoca Road and another on Wilson Avenue, where crews were working to repair a break on Monday morning.

“The pipes themselves do not freeze,” said Young, “but freezing ground temperatures cause the ground to shift” as the ground warms and begins to thaw.  “It’s a small shift, but it does create some issues.”

With temperatures holding below freezing early in the week, the danger of additional water line damage comes with today’s (Wednesday) forecasted thaw.  “We’ll see,” said Young.

As temperatures rise and fall during winter months, homeowners would do well to remember that water pipes running beneath and along exterior walls of their homes are also susceptible to drastic weather shifts.

Residents are advised to leave water faucets running on a low trickle to prevent home water pipes from freezing in severely cold weather.

It is also advised that residents know how to shut off water to the home in the event of a split pipe.

Those who do need help with a problem are assured that TUB will be ready to respond.  Service trucks are housed indoors and heated for ready deployment.

Second Highest

TVA Winter Peak

The Tennessee Valley Authority bulk electric system also remains “secure and stable,” according to TVA chief operating officer Chip Pardee.   Despite the lowest temperatures this area has seen in two decades, TVA announced Monday that electricity demand was expected to be high but not record-breaking.  TVA confirmed Tuesday that the power system had passed a critical demand period early that morning and that the Jan. 16, 2009, record of 32,572 megawatts stands.  However, the preliminary peak demand of 32,460 megawatts at 9 a.m. EST Tuesday as temperatures throughout the valley averaged 4 degrees makes this the second highest winter peak in TVA history by a near margin.

TVA Tuesday praised the region’s 155 local power companies for voluntarily reducing voltage early this week and continues to work with those companies and its directly served industrial customers to ensure an uninterrupted supply of electricity to the 9 million residents of the valley.

As TVA expects electricity use to remain high, valley power companies (including TUB and Duck River Electric Membership Corp.) ask customers to take energy-saving measures to help alleviate stress on the seven-state bulk electric system.  Such measures include turning off non-essential lights and equipment and lowering thermostats by a few degrees.