Pumped Storage Facility
' Location: Raccoon Mountain west of Chattanooga near the Tennessee River ' Capacity: 1,652 megawatts of electricity can be generated for up to 22 hours ' Power source: 528-acre lake stores water that generates peak power through four turbines ' Purpose: Like a giant battery, the plant helps balance TVA's power load by using surplus power to pump water up to the lake during low demand periods and generates power during peak demand by drawing down the reservoir ' History: Construction started in 1970 and was completed in 1978 ' Cost: Initial construction was $310 million and TVA spent $90 to repair cracked rotors from 2012 to 2014. ' Distinction: The mountaintop dam is 230 feet high and 5,800 feet long - the largest rock-fill dam ever built by TVA
Raccoon Mountain is not the place this season to see fall colors or go bike riding.
That's because Raccoon Mountain Road is closed to traffic until Nov. 21: Trucks and heavy equipment will be lumbering up and down the road as the Tennessee Valley Authority inspects and does maintenance to its pumped storage power plant and reservoir.
"Bikes and trucks don't mix," TVA spokesman Scott Fiedler said. "It's a safety issue."
It's a big project. The 528-acre reservoir has been drawn down, and a crew of about 150 people will work 24 hours a day, seven days a week to inspect and repair the mountaintop facility that opened in 1978 and looks like the setting for a James Bond movie.
"We do it every five years," Plant Manager Ken Cornett said.
Tim Babb, senior operator at the Tennessee Valley Authority's Raccoon Mountain Pumped Storage Facility, watches a camera view of the 220-foot-tall water intake structure Friday as the agency drains the 500-acre reservoir in Marion County.Maintenance work will include using LIDAR technology, named for a combination of light and radar, to inspect the reservoir's reinforced concrete water intake structure that at 220 feet is taller than the Statue of Liberty.
Much of the work will take place underground in the chambers and shafts carved into the limestone that hold the four turbine-powered generators, transformers and power cables.
One big repair has been underway for about a year: TVA is replacing 15 giant cables that carry electricity from transformers to the power grid. The old cables had oil that ran through their center to cool them, Cornett said, which TVA worried might cause a fire someday. The new cables aren't oil-cooled, he said, because they're larger and can handle more voltage.
They're huge. Each new cable is between 2,200 and 2,400 feet long and weighs about 15 pounds a foot. The cables are being pulled by a winch up a cable shaft that doubles as the facility's elevator shaft. Tourists used to be able to ride the elevator, but it closed as a security measure after the Sept. 11, 2001, terrorist attacks.
The pumped storage plant works like a battery.
TVA fills the 528-acre reservoir atop Raccoon Mountain at night by pumping Tennessee River water uphill. Doing so burns electricity that TVA has to spare, since its nuclear and coal power plants generally run at full tilt around the clock and demand is down when people are asleep.
When TVA needs a lot of power in a hurry - for example on a 95-degree day when people crank up the air-conditioning - it pulls the reservoir's plug. Water is sucked through the intake structure, which is designed to prevent whirlpools, and blasts down a vertical tunnel drilled through the mountain. It spins turbines that power four generators before it floods out into the Tennessee River.
TVA shut the Raccoon Mountain plant down in March 2012 as a precaution because of cracks in the rotors that spin inside the generators' magnetic field, creating electricity. Because similar rotor cracks caused a catastrophic failure in 2009 at a pumped storage plant in Austria, TVA opted to replace and repair all the rotors.
It took about three years to get the plant fully back online, with all four generators working. But TVA couldn't do the inspections and maintenance while the plant was down, Cornett said, because it had to leave water in the reservoir, which has an earthen dam.
Contact staff writer Tim Omarzu at tomarzu@timesfreepress.com or www.facebook.com/MeetsForBusiness or twitter.com/meetforbusiness or 423-757-6651.