Nearly two years after shutting down its biggest hydroelectric plant to repair a cracked rotor blade, TVA expects to have at least part of the Raccoon Mountain Pumped Storage Plant generating power for the coldest part of the winter.
But most of the idled units at the plant probably won't be back on line until next spring.
Tennessee Valley Authority President Bill Johnson said last week that building and installing replacement equipment for the German-designed facility has taken months longer than expected. The hydro facility shut down in March 2012 when inspectors found cracks in the rotor blade. They were similar to what officials believe led rotors to splinter and destroy another such facility in Austria in 2009.
"We have had difficulty in our recovery plan," Johnson told TVA directors at a board meeting last week in Mississippi. "We originally planned to be done with our first unit several months ago."
TVA Director Neil McBride said it's a lengthy process to forge and produce the massive rotor blades that help convert the water stored in the mountaintop reservoir into electricity when the power is most needed.
But Johnson also said he is holding his own staff responsible for getting the repairs done and the plant back in operation. Last year, TVA estimated the repair cost at $55 million, but the prolonged outage is costing the utility even more to produce or buy replacement power.
"This is a particularly important resource, especially during a peak demand periods," Johnson said. "We have missed it and we need to get it back."
The plant acts like a giant storage battery. During periods of low demand, water is pumped from the Tennessee River at the base of the mountain up to a 528-acre lake carved out of the top of the mountain. It takes 28 hours to fill the upper reservoir, which was erected in the 1970s with the largest rockfill dam ever built by TVA.
The first repaired unit should be ready to test by Thanksgiving and back in service by the end of this year. The other three units are expected to be back in operation by May, Johnson said.
The utility also is installing a new power transformer in the switch yards of the pumped storage plant. Early Sunday morning, Interstate 24 just west of Chattanooga was briefly shut down while 500,000-pound behemoth was trucked from the railroad on Wauhatchie Pike, along Cummings Highway and up Raccoon Mountain Road.
TVA spokesman Jim Hopson said the transformer replacement is unrelated to the problems with the rotor blades and is part of the ongoing maintenance and repairs of the 35-year-old plant.
The rotor cracking problem is a design flaw discovered following the 2009 accident in Austria. Two other similar plants in Virginia and California are undergoing similar rotor replacements.
The 96 rotor poles in the Raccoon Mountain plant -- each 8 feet long and weighing about 7,000 pounds -- had to be inspected and faulty ones replaced with custom-made equipment.
Although all the generators had been running fine, Johnson said TVA opted to shut the facility down and ensure that the rotors didn't have any problems.
"We took prompt , conservative action to shut down the plant, identify the problem and start to fix it," Johnson said.
Getting the Raccoon Mountain hydro unit back in operation is key to TVA's long-term goal of generating at least 20 percent of its power from hydro and other renewable sources, Johnson said.
Contact Dave Flessner at firstname.lastname@example.org or at 757-6340.