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    Rehabs Squeeze More Power from Existing Plants

    The rehabilitation work under way at three existing hydroelectric plants in the U.S. provides a good example of what work is being performed and the benefits that can be expected from this type of activity.

    By Russell Ray and Justin Martino

    At some point, that car you're driving will need a little restoration work. After some machining work and a few replacement parts, it will run a little smoother, get better gas mileage and go from a rumble to a purr. With the right retooling and equipment, you'll get a lot more miles and production out of it.

    With greater significance, the same is true for hydropower plants. Many of the hydro plants in North America are more than 50 years old and are in need of rehabilitation. They represent a phenomenal opportunity to increase the production of renewable energy amid deep concern about climate change.

    plant rehab

    Consider this: A simple rehabilitation can increase a hydropower plant's output by as much as a third. Adding modern hydraulics, new runners and new wicket gates and modifying the draft tube can add a significant amount of clean power to the grid. There are about 2,400 hydropower plants in the U.S. Upgrading those plants with modern technologies could contribute a significant amount of hydropower capacity to the nation's power portfolio without building a single dam.

    What follows are descriptions of three hydropower rehabilitation projects in the U.S. and the benefits that will be seen from this work.

    Cheoah

    On-line Date: 1919
    Value of Work: $110 million
    Expected Completion Date: Fall 2013

    Cheoah project in North Carolina
    The Cheoah project in North Carolina was completed in 1919 and is being rehabilitated at a cost of $110 million through the replacement of four 90-year-old Francis turbines with high-efficiency turbine-generators.

    Cheoah Dam is the site of one of the most famous chase scenes in movie history. In the 1993 movie The Fugitive, Tommy Lee Jones chased Harrison Ford to the end of a series of tunnels within the dam. Ford pledged his innocence one last time: "I didn't kill my wife." Then Jones delivers his legendary line: "I don't care." Ford jumps from the 225-foot-tall dam into the waters far below.

    The famous North Carolina hydropower project was completed in 1919 on the Little Tennessee River, with four turbine-generator units. A fifth unit with an external penstock was added in the 1940s. In addition to Cheoah's memorable place in movie history, it is an important source of clean energy and is being rehabilitated at a cost of $110 million.

    The project's owner, Brookfield Smoky Mountain Hydropower, has upgraded four of the five generating units at Cheoah. Four 90-year-old Francis turbines have been replaced with new high-efficiency turbine-generators and transformers from Voith Hydro and ABB. These improvements, which have been completed except for one section of the substation (to be fully completed later this year), will extend the life of the facility by 40 to 50 years, Brookfield says.

    What's more, the rehab project has already yielded results that far exceed expectations. For example, a 28% increase in capacity for the four units was one of the objectives for the project. Cheoah Dam has actually demonstrated a 45% increase in maximum power output of the four units, from 88 MW to 128 MW, the company says.

    In addition to the capacity improvements, the modernization efforts have eliminated the use of circuit breaker oil and minimized the need for transformer oil through breaker and transformer replacements. The result is a net decrease in total oil volume in high-voltage equipment of almost 40,000 gallons. Also, by using air-cooled transformers, cooling water requirements have dropped significantly, Brookfield says.

    The U.S. Department of Energy awarded Alcoa Power Generating Inc., the former project owner nearly $13 million for the improvements through stimulus money provided by the 2009 American Recovery and Reinvestment Act. Alcoa sold the project to Brookfield in November 2012.

    The first phase of the modernization project was completed in 2012 and involved the upgrade of two of the four turbines and generators. In addition, this modernization effort has replaced the governors, step-up transformers and switchgear. Units 3 and 4 were both completed this summer, with the fourth unit to be upgraded (Unit 3) coming online in July 2013, Brookfield says.

    Webbers Falls

    On-line Date: 1973
    Value of Work: 2.7 million
    Expected Completion Date: June 2017

    Webbers Falls project in Oklahoma
    Three slant-axis turbines are being rehabilitated at the Webbers Falls project in Oklahoma. The turbines, with a rating of 20 MW, are being rewound and upgraded to provide 25 MW of power at all times. (Photo courtesy U.S. Army Corps of Engineers)

    When the U.S. Army Corps of Engineers began the process of rehabilitating the three slant-axis turbines at the 60-MW Webbers Falls plant, they realized there wasn't any precedent on the best way to proceed with the project. This is because only two hydro plants in the world use slant-axis turbines of the size installed at Webbers Falls. The 115-MW Ozark Powerhouse, which is also in the middle of rehabilitation project, features five of the turbines.

    "There was no book on how to rehab slant-axis turbines," Webbers Falls power plant specialist Howard Davidson said. "We took the attitude of a big R and D project."

    Because it was the first time turbines of this type had ever been rehabilitated, Davidson said the contract was written to give Andritz Hydro, the contracting company, more room to determine the best way to proceed with the project. The rehabilitation time will be shorter with each turbine that is rehabilitated.

    The three turbines, rated at 20 MW with a 23 MW overload capacity, are being rewound and upgraded to provide a constant 25 MW of capacity. In addition, the rehabilitated turbines will be easier to maintain and will break less because of design deficiencies.

    The slant-axis turbines, which were built about 40 years ago, were based on a design that was popular in Europe at the time. Davidson said those slant-axis turbines were much smaller, usually 2 or 3 MW, and would run constantly with no maintenance. Replicating the turbines on a larger scale "didn't translate well," he said.

    To make the units larger, a speed increaser had to be added to the turbine, unlike the direct drive system used in smaller slant-axis turbine. The increaser raises the speed from 50 rpm to 514 rpm, Davidson said.

    Many of the problems experienced with the Webbers Falls units were caused by the lack of technology available when the turbines were originally built. Because of some of the deficiencies caused by the technology available at the time, there have been problems with the current turbines, including the main shafts breaking. As part of the rehabilitation, the main shafts are being replaced with larger designs that do not weigh more than the original main shafts. In addition, components are being made of stainless steel to resist corrosion from the Arkansas River.

    "The biggest advantage, and this is the biggest hope for the new design, is to correct the problems from the '60s and '70s," Davidson said. "It just wasn't put together with the technology and know-how we have today. That's what we're doing here. We're taking modern technology that didn't even exist back in the '60s and fixing the problem."

    The rehabilitation was first discussed more than 10 years ago, Davidson said, but took some time to start because the work had to be 100% customer funded before the rehabilitation could begin. The power plant came within 30 days of the contract for rehabilitation lapsing when the Southwestern Power Administration funded the project through customer funding subagreements. The total cost of the project at the time was estimated to be about 2 million.

    Although the first turbine to be rehabilitated has been completed, the unit is currently unwatered after going through testing but will resume operation after some minor modifications are made. Davidson said there is nothing wrong with the unit. "Once that list is done, we're going to water that thing up and get it online and make money off it," he said.

    Davidson said work on the other turbines should go more quickly as the teams learn more about the process of rehabilitating the slant-axis turbines, and estimated the entire rehab would be finished by 2017 at the latest. The finished product will be a clean source of renewable energy that will help provide power without the emissions of other types of power generation, which is one advantage of rehabilitating hydroelectric plants.

    "We didn't have to reinvent the wheel," Davidson said. "We had a structure here with an existing unit. You hate to let anything like this go because, let's face it, they're not building many hydroelectric facilities anymore."

    Badger

    On-line Date: 1908
    Value of Work: $38 million
    Expected Completion Date: Late 2013

    Reconstruction of the Badger Hydro Project
    Reconstruction of the Badger Hydro Project is a massive undertaking that required two cofferdams, the removal of more than 5,000 fish, draining the man-made canal and the removal of several tons of bedrock from the 130-year-old canal. (Photo courtesy The Boldt Company)

    The Badger Hydro Project on Wisconsin's Fox River has been generating power for nearby residents for more than 100 years. The two powerhouses, one in its eighth decade of operation and the other in its 10th, are being replaced by a new powerhouse with 21st Century technology.

    The new powerhouse will have a capacity of 7 MW, up 40% compared with the two old powerhouses. Although the output from this new powerhouse is relatively small, the reconstruction of Badger Hydro is a massive project that required two cofferdams, the relocation of more than 5,000 fish, draining the man-made canal and the removal of several tons of bedrock from the 130-year-old canal. The new horizontal "S" type turbines were supplied by Voith Hydro.

    The widening and regrading of the 2,100-foot-long canal feeding water to the powerhouse will increase water flow and power output.

    The $38 million reconstruction project, overseen by The Boldt Company, is expected to be completed late this year.

    The Badger facility is owned and operated by Kaukauna Utilities, a utility serving 15,000 customers.

    "We knew we had to replace the canal," said Michael Pedersen, manager of generation and operations for Kaukauna Utilities. "It was starting to deteriorate. We were starting to get some leaks."

    Replacing the plants was deemed the best option for customers because the savings will far outweigh the $38 million cost, the utility said. The hydropower plants owned and operated by Kaukauna Utilities have saved its customers nearly 0 million over the past decade compared with the cost of power generated by traditional fuels.

    Repairing the plant would have extended the life of the facility by just 20 years. Rebuilding it means the facility will be able to provide low-cost, renewable power to customers for another 100 years. Retiring the powerhouses and buying replacement power would have cost customers significantly more in the long run, the utility said.

    "We evaluated eight options, and the best long-term cost option was to build the new powerhouse and remove the four units," Pedersen said. "This was the most economical way to go."

    Of the $38 million cost, about $10.5 million was spent on widening and upgrading the canal. The canal improvements were mandated by the Federal Energy Regulatory Commission as part of the project's operating license.


    Russell Ray is managing editor and Justin Martino is associate editor of Power Engineering, a PennWell publication. This article previously appeared in that magazine.

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