The Nashville District of the U.S. Army Corps of Engineers is six years into a US$1.2 billion 20-year rehabilitation and modernization program for nine hydropower plants it operates in the Cumberland River system that originally began operating between 1948 and 1977.
By Jamie G. James
In 2004, the Nashville District of the U.S. Army Corps of Engineers embarked upon the Cumberland River System Hydropower Rehabilitation Program, a US$1.2 billion program using funding granted by the U.S. Congress in the Water Resources Development Act of 2000, along with normal appropriations.
This program is intended to repair, rehabilitate, replace and modernize hydroelectric generation equipment in each of the nine plants. The program goals include increased reliability, availability and efficiency of equipment; effective use of modern technology; best use of available natural resources; and effective use of financial resources.
This article describes the program scope, funding, priorities, execution strategy and progress to date.
Cumberland River system
The Nashville District operates nine hydropower plants along the Cumberland River that began operating between 1948 and 1977 (see sidebar on page 21). Each plant’s turbine-generator units have been operated beyond their expected design life and have begun to suffer declines in efficiency and reliability in spite of a robust maintenance program.
The Cumberland River System hydropower resource is a significant part of the regional power portfolio. In fiscal year 2016, the sale of the 3 million MWH of hydropower generated resulted in revenue of more than $65 million.
Regionally, power is supplied by a mix of hydropower, coal and nuclear facilities. Water availability, other authorized purposes and missions for Corps dams, and other generation sources mean that hydropower is typically used as a peaking source in the southeast U.S. In recent years, other renewables (such as wind and solar generation) have been introduced into the region but not in sufficient quantity to assume baseload generation or full peaking capacity.
Most of the generation equipment at the plants is original and well past normal design service life.
The Corps evaluates the condition of plant equipment on an annual basis and performs planned maintenance outages. Over time, there has been a decline in performance. For example, in the mid-1990s the Corps experienced a reliability rate in the mid to high 90% range, which means more than 95% of the time when a unit received a call to operate, it would respond without issue.
During the past 10 years, reliability has declined into the 80% range. When reliability reaches this range, it is an indication material problems exist. As a result of this decline, the length of time in performing maintenance increases during planned outages.
|This map shows hydropower projects operated by the U.S. Army Corps of Engineers’ Nashville District (see sidebar on page 21 for more info).|
Some of the units at plants in the Cumberland project were commissioned in the 1940s and others in the 1970s. With the exception of the few that have been rewound, every generator is past its intended service life. The average age of equipment is about 59 years.
The Corps has robust standards and programs of maintenance and operation. Part of equipment maintenance includes entering the condition of equipment in a monitored database and planning outages that occur at varying intervals or frequency.
Modernization will improve efficiency
By delaying hydropower equipment rehabilitation and modernization, the Corps has foregone the advantages of 60+ years of technological progress and the increased power production and more efficient water use that accompanies that progress. The older equipment is not able to operate at the same level of precision as newer equipment (i.e., digital governors compared to mechanical, and electronic control systems).
The Corps plans to install auto-venting turbine runners at two plants that will help increase levels of dissolved oxygen (DO) within reservoir waters. This will allow for continued generation when otherwise, DO levels in the reservoir would not be optimal to put this water downstream. Taking advantage of advances in turbine design and control systems will allow for more efficient operation of units, which means the district will use available water resources to generate more power, more efficiently.
In addition to the problems of equipment age and failure, federal budget dollars became scarcer with increased competition for resources. There has been widespread need for modernization across the 75 plants in the Corps hydropower community because the infrastructure is aging.
Hydropower infrastructure is not alone in this dilemma, as the nation’s highways and utilities share these concerns and compete for federal funding. This has contributed to the shortage of monetary resources, which has caused many systems to delay or defer major rehabilitation and modernization of hydroelectric assets.
There are many challenges in the district. Any plans for improvement must include preserving operational capacity. In addition, the plan must call for rehabilitating and modernizing equipment, using water resources efficiently and effectively across business lines and purposes, and maximizing the impact of available funding. Executing the plan must be paced in such a way that the recapitalization of equipment does not cause Cumberland River System hydropower to be unaffordable or exceed the limits of human resources capacity to complete the work.
|Aging hydroelectric generating units operated by the district at dams in Kentucky and Tennessee have gone well beyond their typical design life of 35 to 40 years. (Photo by Mark Rankin)|
All this must be done while balancing the needs of internal and external stakeholders, considering the physical condition of equipment, looking at the relative system value of competing needs, and examining the technical and business aspects of proposed work. By working with stakeholders and technical experts, the Nashville District has prepared a program to attack these challenges.
With federal budgets directed to hydropower operations and maintenance being relatively flat over recent years, it has been difficult to obtain federal funding for major rehabilitative work on hydropower equipment. Congress recognized this funding challenge and took action. In WRDA, Congress made it possible for the Secretary of the U.S. Army to accept funds from power preference customers for the maintenance and modernization of hydroelectric equipment. This was an important turning point for the Cumberland River System, resulting in a partnership between the district, the Southeastern Power Administration that markets the power produced, and power preference customers to perform needed capital work on the system. This partnership is known as Team Cumberland.
The district’s customer-funded hydropower rehabilitation program is called Section 212 Hydropower Rehabilitation Program, named after the authorizing section in WRDA. The program began with a series of short-term memoranda of agreement (MOA) in FY2004. The MOA are required to be executed by the Assistant Secretary of the U.S. Army for Civil Works, but local authority has been granted to the Nashville District Commander to execute sub-agreements valued up to $25 million.
|Work crews lifted the turbine runner out of Unit 2 in the powerhouse at Center Hill Dam on Oct. 7, 2015. The Nashville District is rehabbing all three units in the powerhouse. (Photo by Lee Roberts)|
The short-term MOA had two-year terms, and the last executed was the FY08-09 MOA. These MOA combined to provide $45 million to the system, with $35 million used for needed projects and $10 million retained in a reserve fund. In 2011, recognizing the inefficiency inherent in short-term MOA, a portion of the external stakeholders entered into a 20-year MOA. A series of sub-agreements have been used to authorize and fund work on the Cumberland River System since then, but funding fell short of projections, which affected program work. Even so, the power preference customers have provided $160 million through the 20-year MOA for program work in the Cumberland River System.
In 2016, additional stakeholders entered into another short-term MOA directed toward funding major hydropower rehabilitation work at the Barkley powerhouse. This MOA also has a two-year term, and efforts are under way to extend the MOA to provide full funding for the work. In FY2016, this MOA contributed nearly $23 million toward work at Barkley. All of the MOA that have been executed in support of the Cumberland River System have been controlled by governance groups comprised of stakeholders from Team Cumberland. These governance groups review work proposals developed by the Corps.
The groups examine compliance with the MOA and intent of the Master Plan and vote to authorize the scope, schedule and budget of each project. Work authorization is accomplished within sub-agreements. Changes to the scope or budget are authorized by the group through use of a ballot, and ballots are also used to authorize work using excess project funds from other authorized work. Both sub-agreements and ballots require unanimous approval from the governance group.
Normal design service life of hydroelectric generation equipment is typically 35 years, so system equipment has performed well beyond expectations. In the nine plants in the Cumberland River System, there are 28 turbine-generator units, along with their supporting systems of exciters, generator cables, governors, transformers, and other equipment necessary to generate power and transfer that power to the grid.
Each plant has a staff that advocates for needed work, and there is no doubt each plant needs the work that is planned within the Section 212 Program. However, because of the cost, available annual revenue, equipment condition, and business considerations of executing the program, the Nashville District had to establish priorities and craft a plan to execute the program of work in an efficient and effective manner. To that end, in 2011 the district completed the first Program Master Plan.
This plan was completed with the assistance of the Corps’ mandatory center of expertise, the Hydroelectric Design Center, and the consulting engineer under contract at that time, Montgomery Watson Harza, along with input from internal and external stakeholders.
The Cumberland River System Hydropower Rehabilitation Master Plan is a living document that is periodically revised. System equipment casualties, funding changes and priority realignment require occasional adjustments in execution. So, provision is made for plan updates that consider each of these factors and include stakeholder input.
Studies of major components such as switchyards and turbine governors have been undertaken to refine the assumptions in the plan, as well as plant studies that focus on the turbine-generators and affected downstream equipment. All of these factors have resulted in an update that was effective in April 2014 and another update that is in progress in 2017. The Corps expects to have the master plan update by 2018.
Program priorities are aligned to maintain generation capacity, modernize equipment, and support the continued ability to provide power to the grid. This means that priority is given to turbine-generator units, followed by equipment needed to support the units and transfer power to the grid.
Current state of the rehab program
The Nashville District has two active MOA with its power preference customers that are being used to authorize and fund work on the Cumberland River System hydroelectric facilities. One MOA, known as the Long-Term MOA (L-T MOA), was signed in August 2011 and expires in September 2032.
The L-T MOA partners purchase slightly less than half the power produced by the system. The second MOA, known as the Short-Term MOA (S-T MOA), was signed in June 2016 for a two-year term. A two-year extension is being considered. While these MOA provide the overarching authority to conduct the program, specific project work authorization and funding are accomplished through sub-agreements.
As the program has moved forward, the district has undertaken a number of projects to accomplish system goals. All of the project activities are too numerous to detail, but a few of the representative projects are briefly discussed.
The Nashville District is well into the Center Hill Major Hydropower Rehabilitation. This project will replace the 45-MW Francis turbine runners with self-aerating turbine runners and rewind the three GE generators at the plant, which came on line in 1950. The benefits of this work will include an incidental uprate of capacity to 52 MW, greater reliability and availability of the units, and increased DO in the Caney Fork River downstream. Center Hill is the first plant in the Cumberland River system to undergo major rehabilitation. The construction contract was awarded in 2014 to Voith Hydro for $47.2 million and is scheduled for completion in 2019.
Planning has been completed and engineering and design is under way for the Barkley Major Hydropower Rehabilitation to revitalize the four 32.5-MW units that came on line in 1966. The district expects to issue a contract solicitation in 2019. This project will replace the Kaplan turbine runners, restack the core, rewind the units to 41.85 MW, and complete associated work. There are no challenges related to DO in the Cumberland River downstream of Barkley Dam, so the benefits of this project will be an incidental increase in plant capacity and greater reliability and availability of the units.
On Feb. 17, the district awarded a contract to replace the excitation at Barkley. The existing excitation consists of an amplidyne unit. Because of the age of the equipment and arc flash considerations, the district decided to install static digital excitation and remove the rotational equipment from the units. The project was awarded to Canadian Commercial Corp. for a bid of $3.36 million. This work is being completed in advance of the major rehabilitation work at the plant that will rehabilitate the turbines and generators.
In January 2017, the district began engineering and design to replace the main power transformers at the Barkley Power Plant. The existing transformers are aging and not sufficient in capacity to support the major rehabilitation of the turbine-generators at the plant. A solicitation to acquire the transformers should be announced in 2018.
The Nashville District began engineering and design for the Old Hickory Major Hydropower Rehabilitation, the third major rehab project, this year. This project will include the rehabilitation or replacement of the turbine runners, rewinding the generators, restacking the cores and associated work. Benefits will include an incidental uprate of plant capacity and improved reliability and availability of plant equipment. Solicitation of this contract is scheduled for 2023.
Prior to beginning the scheduled rehabilitation program for the Old Hickory facility, in 2013 Unit 4 experienced a turbine-strike casualty. This issue caused the district to take the unit out of service and plan repairs.
Contact between the turbine runner and discharge ring was apparently due to misalignment related to movement in the concrete structure. Forensic examination revealed that the movement was related to thermal expansion of the concrete. Concrete testing and monitoring for more than one year showed the movement is stabilized.
The district completed 90% of plans for the project in 2015 to repair the Kaplan turbine runner and rewind and realign the unit to restore full operation.
In March 2017, GE /Alstom was awarded a contract to make repairs, with an expected return to service by July 2019. The generator windings are 60 years old, which led to the decision to rewind the generator rather than risk damage during movement. The new windings will be of sufficient capacity to support major rehabilitation of the Old Hickory plant.
The district has completed a number of smaller projects throughout the system, such as breaker replacement, replacement of bridge cranes at Old Hickory and Barkley, and planning studies. The planning studies have been used to add detail to the Master Plan by formulating the rehab strategies at the various plants, or establishing needs and priorities for rehabilitation of the many common components throughout the Cumberland River System, such as switchyards. These smaller projects have been used to set the stage for major rehab work on the turbines and generators at the plants.
Jamie G. James, PE, is a project manager with the Nashville District, U.S. Army Corps of Engineers.
James, Jamie G., “Cumberland River System Hydropower Rehabilitation Program,” Proceedings of HydroVision International 2017, PennWell Corp., Tulsa, Okla., 2017.
Emergency repairs made at Barkley
Separate from the Cumberland River System modernization, Ohio-based National Electric Coil and Hydro Consulting & Maintenance Services worked on an emergency rewind at the 130-MW Barkley hydro plant after a phase-to-ground fault caused a fire on Dec. 19, 2010, that damaged the generator stator windings on one unit.The unit was returned to service on Dec. 6, 2013.
The US$11.5 million major repair project began Aug. 15, 2012, when contractor employees lifted the 270-ton assembly by crane and placed it on a nearby pedestal for repair by NEC, said Jamie James, a project manager with the Corps’ Nashville District.
After a complete inspection of the disassembled unit, it was determined that a complete generator stator rewind would be required. The 47-year-old unit was initially placed on line in 1966.
Corps plants in Cumberland River System
The Nashville District of the U.S. Army Corps Engineers will rehabilitate 28 units at its nine hydropower projects in the Cumberland River system. The plants are:
- 130-MW Barkley, on the Cumberland River about 22 miles southeast of Paducah, Ky., contains four 32.5-MW units and became operational in 1966.
- 135-MW Center Hill, on the Caney Fork River in Dekalb County, Tenn., 55 miles east of Nashville, contains three 45-MW generating units that became operational in 1950 and 1951.
- 36-MW Cheatham, on the Cumberland River about 15 miles southeast of Clarksville, Tenn., contains three 12-MW units that became operational between 1958 and 1960.
- 99.99-MW Cordell Hull, on the Cumberland River about 48 miles east of Nashville, contains three 33.33-MW units that became operational in 1973 and 1974.
- 54-MW Dale Hollow, on the Obey River in Clay County, Tenn., contains three 18-MW units that became operable in 1948, 1949 and 1953.
- 28-MW J. Percy Priest, on the Stones River about 10 miles east of Nashville, contains one unit and became operational in 1970.
- 61-MW Laurel, on the Laurel River in Laurel and Whitley Counties, Ky., has one unit and became operational in 1977.
- 100-MW Old Hickory, on the Cumberland River about 14 miles southwest of Gallatin, Tenn., contains four 25-MW units and became operational in 1957.
- 270-MW Wolf Creek, on the Cumberland River about 10 miles south of Jamestown, Ky., contains six 45-MW units that became operational in 1951 and 1952.