TVA upgrading hydro operations, increasing efficiency

By Kathy Helms-Hughes

   It will probably take Tennessee Valley Authority 15 years to upgrade more than 100 units at its 29 hydroelectric dams, but once completed, the increase in efficiency will be equivalent to building a brand new plant.
   Mark Pipkin is production manager for TVA's hydro operations at Watauga, Wilbur, Boone, South Holston and Fort Patrick Henry dams.
   According to Pipkin, TVA completed upgrades at Fort Patrick Henry in 1996 and will begin modernizations on Boone in 2004 and Watauga in 2007. At Fort Henry, TVA replaced the water wheels, installed new turbines, upgraded the generator and generator leads, and put in a new static exciter.
   "We did a survey on the machines and decided where to spend our money first. This plant was a higher priority because of the amount of water that goes through here," Pipkin said. Modernizing the units also cuts down on maintenance costs.
   According to Gil Francis of TVA Media Relations, the upgrade includes updating controls from analog to digital so that some things which were done manually can now be done automatically.
   Turbines also are being replaced. "The ones from the '30s were OK, but the ones today, the technology is better," Francis said.
   The cost to upgrade depends on the powerhouse, said Pipkin, as he and Francis took Star staff on a tour of Fort Patrick Henry Dam. "Some units you may be able to do for $500,000 to $600,000. Some may be $1.5 million. These units here are about 35,000 horsepower. There are some out there that are 55,000 hp. The bigger the machine, the more it costs."
   Fort Patrick Henry is a massive structure of concrete and steel. On the inside wall of the dam are the words, "Built for the people of the United States of America," along with the date construction began (1951) and the date of completion (1954).
   According to TVA data, just to construct the dam alone, a total of 570 people labored 1,719,879 man-hours, and with only six injuries. During construction of the dam and powerhouse, 66,700 cubic yards of dirt and 159,500 cubic yards of rock were moved. Workers poured 70,500 cubic yards of concrete and set 1,337 tons of reinforced steel along with 941 tons of structural steel.
   Fort Henry's two turbines spin at 138 rpms and each has the capacity of about 22 megawatts per machine, or an output of 44 megawatts.
   The turbines can be operated in two modes, Pipkin said. "One is the most efficient loading. In other words, we've got a curve where we get peak generation with a certain amount of water. Then we can go to maximum generation, which would be the 44 megawatts. We like to generate at the most efficient point, getting the most dollar value from the water."
   Prior to refurbishing, the water wheels from 1951 were essentially hand-crafted, he said. "The water wheels that we have now are computer generated, so the efficiency of the machines, of course, went up with the better water wheel. That was completed in 1996. Along with that, we had to upgrade the power train, which meant that the generator leads that go from the generator out to the transformer had to be increased in capacity.
   "Also at this time, we put a new excitation system in. This excites the generator and is what builds the megawatt output. Before, we were able to get about 18 or 19 megawatts out of the machine and now we're pushing 22 with less water."
   A governor cabinet controls the speed of the unit. "If there's no way to control the speed of the water wheel, it can run away with you. It's set to keep the machine at 60-cycle speed," he said.
   Hydraulic oil pressure is used to open and close the wicket gates, which allow water to hit the water wheel. Those wicket gates also are controlled by hydraulic oil pressure. The turbines are known as kaplan units, meaning they have blades akin to a propeller on a boat motor. "Except on these machines, the props pitch. As these wicket gates open, the prop -- or water wheel -- changes pitch to get the most efficient use of the machine," Pipkin said.
   "They came up with this technology in the late 1930s, refined it in the '40s, and we started building these plants in the '50s. That technology would still be employed today if you were going to build a new one of these."
   Output of the generators when generating is 13.8 kv (13,800 volts) before it comes into contact with a transformer. The distribution voltage which leaves the step-up transformer is 69,000 volts. From there, it goes out over the transmission lines to surrounding substations and co-ops which feed off TVA lines and distribute the power to local homes and businesses.
   "Big industry, like the Saturn plant, or USEC [U.S. Enrichment Corp.], or Alcoa Aluminum will feed directly because the power requirements are so big, and the lines will be higher voltage, too," Francis said.
   "By the time it gets to you, of course, it's 120 volts because that transformer outside your house cuts the voltage back down."