Christopher F. Vick, Bureau of Reclamation, U.S. Department of the Interior
May 05, 2013 | 2 Comments
Work several years in the making is about to commence at the Third Power Plant of the 6,809-MW Grand Coulee project in Washington. Rehabilitation of all six units, including potential uprating of three of them, will ensure continued reliable operation of this valuable asset and a possible extra 240 MW in generating capacity.
As the largest hydroelectric facility in the U.S., the 6,809-MW Grand Coulee project on the Columbia River in Washington is integral to power generation in the Pacific Northwest. The most recently commissioned powerhouse at the dam, the 4,485-MW Third Power Plant, began operating in 1975. The six units are reaching the end of their design life and require significant rehabilitation.
The U.S. Department of the Interior's Bureau of Reclamation, plant owner and operator, has spent several years planning this rehab. Work on the overhaul of three of the six units will commence in March 2013 and is scheduled to be complete in September 2017. Reclamation also is investigating the scope of the work on the remaining three units, and this work is scheduled to begin in January 2018 and be completed in December 2022. When complete, the plant should operate reliably for another 30 to 40 years.
Background on the Facility
Construction of Grand Coulee Dam began in 1933 and was completed in 1941. The dam is part of the Columbia Basin Project, providing water to irrigate more than 600,000 acres, and is the cornerstone for water control on the Columbia River in the U.S.
The dam impounds water for three plants. The Left Power Plant began operating in 1941 and contains 12 turbine-generating units with a total capacity of 1,155 MW. The Right Power Plant began operating in 1949 containing nine units with a total capacity of 1,125 MW.
Construction of the Third Power Plant, which contains six units with a total capacity of 4,215 MW, began in 1967. The first unit in this powerhouse was commissioned in 1975, and the final unit was commissioned in 1980. The cost of construction was about 30 million, and the plant generates more than $500 million in revenue annually.
The six units in the Third Power Plant are designated G-19 through G-24. Units G-19, G-20 and G-21, rated at 600 MW each but operated at 690 MW, are equipped with 820,000-horsepower Francis turbines with a runner throat diameter of 34 feet, designed by Dominion Engineering Works Ltd. and manufactured by Willamette Iron and Steel Co. Units G-22, G-23 and G-24, rated at 805 MW each, are equipped with 960,000-hp Francis turbines with a runner throat diameter of 32 feet and were designed and manufactured by Allis-Chalmers.
The six Third Power Plant units have been in continuous use since commissioning, with the exception of routine maintenance cycles, unscheduled outages (as a result of a 1981 fire in the cable tunnel), and stator repairs that were performed in the 1990s on Units G-22, G-23 and G-24. These generating units, the cornerstone for peak loading and balancing for the Federal Columbia River Power System, experience frequent load changes and are commonly operated in synchronous condense mode.
All six of these units, which range in age from 33 to 38 years, are nearing the end of their design life, and the frequency of unscheduled, forced outages is increasing. As a result of the units' decreased reliability and increased unscheduled maintenance, Reclamation and the Bonneville Power Administration (BPA) decided in 2008 to overhaul all the units.
BPA is a regional federal agency that markets power from all federal hydroelectric projects in the Pacific Northwest. BPA, situated within the Department of Energy, is self-funded with ratepayer dollars. The funding for operations, maintenance and capital projects at Grand Coulee Dam is provided by BPA, which is also funding the overhaul of the Third Power Plant.
This overhaul program, consisting of nine pre-overhaul projects and the mechanical overhaul of the six units, is expected to cost about $400 million. It will be completed in stages, and a contract was awarded in May 2011 for work on Units G-22, G-23 and G-24, which is scheduled to be complete in 2017. These units, which have an annual production value of more than $250 million, are in worse general condition than Units G-19, G-20 and G-21. Although Units G-19, G-20 and G-21 are older, they are more mechanically robust than the lighter, higher-rated units G-22, G-23 and G-24. Therefore, Units G-22, G-23 and G-24 have more mechanical issues that need to be addressed sooner.
A second contract will be awarded in the future for work on Units G-19, G-20 and G-21.
Planning the Overhaul
Reclamation prepared for the mechanical overhaul of all six units by performing extensive planning. Personnel developed a project management plan to guide the process, which initially included high-level estimates of scope, schedule and budget. The planning phase focused on refining the scope, schedule and budget while developing a risk register and quality management, communication, human resources and procurement plans.
A risk register is a document that contains all potential, identifiable risks that are inherent within a project. The risk register is a matrix-based document where a risk that is more likely to occur, with a larger impact to the project, ranks higher than a risk that is less likely to occur, with less potential impact to the project. Each of these risks are then assigned a response. If the risk is realized, Reclamation knows how to respond.
A considerable amount of the planning phase work was accomplished in partnership with architect/engineering companies under contract with Reclamation, including MWH Americas, CH2M Hill Inc. and HDR Inc. These efforts will result in improved reliability of necessary equipment, identify ways to minimize outage durations, and reduce the likelihood and magnitude of increases to outage time.
There is a saying that living in a home while it is being renovated is more challenging than building a new home. This saying applies to the logistics of overhauling the Third Power Plant while maintaining a fully functioning hydropower facility. A large amount of lay-down space is required for all the turbine and generator parts as they are removed. More space is required during the overhauls than for initial construction of the units, when parts were delivered as needed. Each unit has several large and heavy items that require special consideration. These items and their dimensions for the three 805-MW units are: