Repairs at the Tennessee Valley Authority’s 1,616-MW Raccoon Mountain Pumped-Storage Plant are not expected to be completed until sometime in 2014, TVA said in its Nov. 18 annual Form 10-K report.
The four units at Raccoon Mountain were placed into service during 1978 and 1979. The units, with a total net summer capability of 1,616 MW, are used to balance the transmission system as well as generate power. Pumped storage involves expending electricity by pumping water uphill during slow power demand periods, so that the water can be released to cascade downhill and generate power during peak demand times.
“Inspections of the turbines in the four units of Raccoon Mountain during 2012 found cracking in the rotor poles and the rotor rims,” TVA reported. “Because the same type of cracking led to the catastrophic failure of a similar unit in Europe, the Raccoon Mountain units were taken out of service. Raccoon Mountain Unit 2 returned to limited service with a partially restacked rotor in October 2012, but was taken out of service again on January 3, 2013, due to a failed rotor pole clamp. All units are undergoing a maintenance overhaul and are expected to be returned to service in 2014. TVA is dispatching generation from other TVA units and purchasing power if needed to compensate for the loss in generating capacity.”
TVA maintains 29 conventional hydroelectric dams with 109 units throughout the Tennessee River system and also the Raccoon Mountain pumped-storage facility. As of Sept. 30, 2013, which was the end of this federal utility’s latest fiscal year, these units accounted for 5,433 MW of summer net capability.
The actual amount of electricity that TVA can generate from its hydro plants depends on a number of factors, including the amount of precipitation and runoff, initial water levels, and the need for water for competing water management objectives. The electricity generated also depends on the availability of the hydro plants. In addition, four hydroelectric dams owned by a third party on the Little Tennessee River and eight U.S. Army Corps of Engineers dams on the Cumberland River contribute to the TVA system.
Reliability upgrades have added 422 MW of capacity
In 1992, TVA began a Hydro Modernization Program to address reliability issues on its conventional hydroelectric units and at Raccoon Mountain. As of Sept. 30, modernization had been completed on 55 conventional hydro units and four pumped-storage units. These projects resulted in 422 MW of increased capacity on the conventional units, with an average efficiency gain of about 5%.
“Hydroelectric generation will continue to be an important part of TVA’s energy mix,” the Form 10-K added. “TVA, through its Hydro Modernization Program, continues to assess its remaining conventional hydroelectric units for opportunities to improve reliability and increase capacity.”
Hydro has been very good to TVA lately. After several years of drought in the TVA service area, rainfall totals improved during 2013 and 2012. Rainfall in the Upper Basin of the Tennessee Valley was 124% of normal for 2013 and 102% of normal in 2012. Runoff was 143% of normal in 2013 and 98% of normal in 2012. Runoff is the amount of rainfall that is not absorbed and actually reaches the rivers and reservoirs that TVA manages. TVA’s conventional hydro generation increased 39% in 2013 as compared to 2012, and decreased 2% in 2012 as compared to 2011. Conventional hydro generation was about 126% of normal in 2013 and 90% of normal in 2012.