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.
By Christopher F. Vick
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.
|The 4,485-MW Third Power Plant at Grand Coulee Dam contains six turbine-generator units that are reaching the end of their reliable lives. A rehabilitation project is under way that will see all six units rehabilitated and three units upgraded, increasing total plant capacity by 240 MW.|
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 (see Figure 1).
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:
- Upper bracket (diameter 83 feet);
- Rotor (diameter 58 feet);
- Main support bracket (diameter 45 feet);
- Head cover (diameter 35 feet);
- Operating ring (diameter 25 feet); and
- Three main shaft sections (diameter 11 feet), which must be stored vertical ly to avoid distorting their concentricity.
It is expected that these large parts will occupy most of the floor space except for access aisles needed to move smaller components. In addition, contractor equipment and material must be stored throughout the powerhouse.
Reclamation selected MWH Americas of Bellevue, Wash., in March 2009 to prepare a logistics study of the powerhouse overhaul. MWH Americas personnel presented a report in September 2009 documenting the ideal arrangement for component lay-down areas as the first three units are overhauled, while maintaining adequate work space for operations and maintenance personnel and activities (see Figure 2). MWH Americas personnel also presented alternative scenarios, including a suggested lay-down arrangement if another of the three 805-MW units or one of the 690-MW units failed during the overhaul and required complete disassembly.
To help show stakeholders the sequence of events and complexity of the overhauls, the contractor also developed a computer simulation showing an animation of the base scenario. This simulation can be viewed at www.usbr.gov/pn/grandcoulee/tpp/index.html.
Risk is inherent with all endeavors. Because of the significant role the Third Power Plant units have with regard to the regional power structure, it is imperative that all risks associated with this work are identified, analyzed, monitored and controlled. To populate the risk register, Reclamation gathered its subject matter experts and used a brainstorming technique to identify potential risks.
Qualitative and quantitative risk analyses were then employed to develop a probability and impact matrix that ranked each risk based on probability of occurrence and magnitude of cost. The risk register was then further defined to include a prioritized list of risks and associated risk responses. The risk responses include strategies for risks that: have negative impacts, thatpresent positive opportunities (such as cost and schedule savings); or require expert judgment based on the scenario in which they are encountered. The risk register is continuously updated to reflect current project conditions.
Designing the overhaul
Reclamation's Technical Service Center designed the mechanical overhaul of units G-22, G-23 and G-24. This center is a world-class engineering, science, research and support center for projects related to water resources.
The overhaul design specifies complete disassembly of each unit. The generator and turbine components will then be inspected for cracks and other indications. The thrust bearing will be sand blasted and recoated. The thrust bearing oil coolers and associated piping will be replaced. The rotor poles will be removed, inspected and re-installed. The stator cooling water system will be completely replaced. The 24 wicket gates on each unit will be removed and examined.
Nine new wicket gates are being fabricated to ensure gates are available if a problem is discovered that requires gate replacement. The outer and inner head covers will be examined and then rehabilitated and machined to ensure the critical surfaces are appropriately configured. The runner will be examined, and cavitation damage will be repaired, but the planning effort concluded that runner replacement is not necessary. A new set of stationary and rotating wear rings will be machined and installed on each unit.
Finally, each unit will be reassembled, commissioned and returned to service.
Beginning the work
Through a request for proposals process, Andritz Hydro Inc. of Charlotte, N.C., was selected as the contractor to perform the construction phase of the mechanical overhaul. Andritz Hydro was to begin the $102 million construction phase in March 2013 and complete work on the last unit in June 2017. The contractor will construct a temporary building to accommodate the painting, sandblasting, storage, machining and assembly needs.
Work to complete before the overhaul
During the 10-year rehabilitation program, the plant will operate with at least one unit off-line, making it imperative that the remaining units function as reliably as possible. To ensure reliability, the Reclamation maintenance database, CARMA, was investigated to determine causes for unscheduled (forced) outages. The causes were ranked based upon frequency. The most frequent causes of unscheduled outages were: excitation failure; governor malfunction; transformer gassing; and shear pin, shaft seal and thrust bearing failures.
An executive decision was made to address the most frequent causes of unscheduled outages either through the mechanical overhaul or as independent projects. The independent projects that required completion before the mechanical overhaul could begin are: erection of 500-kV overhead lines, construction of a material storage building, excitation system replacement, governor replacement, crane controls replacement, fixed wheel gate chamber modifications, and installation of new main unit transformers for G-19 and G-20.
500-kV overhead lines
Underground, oil-filled cables transmit power to the 500-kV switchyard. In 1981, a single phase of an oil-filled cable faulted, destroying all circuits in the tunnel that houses the transmission lines for Units G-22, G-23 and G-24. The resulting fire removed 2,415 MW of capacity from the grid. It took about two years to plan, design and construct temporary overhead lines and another three years to replace the oil-filled cables. The overhead lines were then abandoned in place.
It has recently become apparent that the condition of underground oil-filled high-voltage cables is degrading. At the same time, it has been determined that Units G-19, G-20 and G-21 could each be uprated from 690 MW to 770 MW if the cables were replaced with higher-capacity transmission lines.
Converting to overhead transmission lines solves several problems: Overhead lines can be inspected and maintained more safely; the new lines can support uprating of the three units mentioned above; and using an overhead route does not require long periods without generation to remove old and install new cables. This switch only constitutes a two-week outage per generating unit, while replacing the oil-filled cables would take at least a year and cost more than $250 million in lost generation revenue.
Based on these factors, Reclamation decided to remove the oil-filled cables and install overhead transmission lines.
Reclamation approached BPA in 2009 to assist in planning, designing and constructing the 500-kV overhead lines. The $18.5 million project was awarded in January 2012 to Wilson Construction or Canby, Ore. The new overhead lines were energized in December 2012, and the oil-filled cables will be removed by December 2013.
|Because of the sheer amount of lay-down space required to disassemble and inspect each of the six units in the Grand Coulee Third Power Plant, the Bureau of Reclamation hired a contractor to build a material storage building. This building provides secure, climate- and temperature-controlled storage space.|
Material storage building
Overhaul of the turbines and generators requires lay-down space for parts as they are removed. These and other incidental parts, such as piping and valves, will occupy nearly all the powerhouse floor space. In addition, a variety of spare parts and pieces are being stored in the Third Power Plant - such as transformer bushings, rotor poles and stator laminations - that must be removed to provide the overhaul lay-down space. These valuable and easily damaged spare parts need to be kept in a secure, climate- and temperature-controlled storage space.
A design/build contract was awarded in March 2011 to Graham Construction of Spokane, Wash., for $5 million. The Grand Coulee Dam facilities are part of a historically significant area. This storage building cannot detract from the overall appearance of the area, so it was designed to be significantly smaller than the Third Power Plant but incorporate many of the architectural aesthetics of the plant.
The storage building was constructed adjacent to the Third Power Plant, providing a convenient location for material movement. The building includes a 100-foot-by-200-foot floor area with 50-foot-tall walls, 30-foot-by-28-foot door (same size opening as the north powerhouse door), insulated walls and ceiling, heating and cooling, forced ventilation, power, compressed air, and a life safety system with fire suppression. The building is also certified LEED Silver.
The project was considered substantially complete in October 2012. Grand Coulee personnel have begun moving material from the powerhouse into the storage building and expected to have the building full by March 2013.
Excitation system replacement
The excitation systems and associated equipment for the six generators are being replaced with more robust and modern equipment. The excitation systems were state-of-the-art when supplied in the late 1970s, but the components have become obsolete and are difficult to replace. In addition, failures associated with the excitation systems have created frequent unscheduled, forced outages of the generators.
The construction phase of the $22 million project was awarded in April 2010 to ABB Inc. of Montreal, Quebec, Canada. All six units are now operating with the new excitation system.
The generators have a major role in reacting to normal load swings but also in reacting to power system transient conditions, such as loss of critical transmission paths or varying load. However, the units have been experiencing failures and erratic behavior and therefore have not been responding as quickly as possible.
The six governor control systems are being replaced with digital governor controls. The new, faster-responding governors allow for a more stable response to load rejection. The governor hydraulic systems are in good condition and have not experienced major problems, so the scope of this project is limited to replacing the electronic components and pilot valve.
The construction phase of the $3 million project was awarded in May 2010 to American Governor of Amherst, Wis. All of the new governor systems are online.
Crane control replacement
There are six cranes in the Third Power Plant: two 275-ton upper bridge, one 50-ton upper bridge, one 2,000-ton lower bridge, one 70-ton draft tube gantry, and one 275-ton forebay gantry crane. Repair and upgrade of these cranes was the subject of an inspection and report by CH2M HILL and Coffman Engineers that was completed in September 2008. The report recommended limiting work to crane control replacement. The $17 million crane controls project was designed by CH2M Hill, and the construction work was performed by Dix Inc. of Spokane, Wash. The project was scheduled to be complete by February 2013.
Fixed wheel gate repair chamber modifications
Each unit has a single fixed wheel gate, or head gate. Routine inspection and overhaul of these gates takes substantial manpower and unit outages. The outages required for each unit's mechanical overhaul are an ideal time to inspect and overhaul the gates. However, the fixed wheel gate chamber itself no longer complies with current life safety and electrical codes. The wiring is not explosion-proof, ventilation is inadequate, separation from the dam galleries is insufficient, and lighting is poor. Compounded, each of these factors led Reclamation to extensively modify the chamber to ensure it is fully compliant with all applicable codes and regulations.
The $4 million project was designed by Reclamation and was constructed by Knight Construction of Spokane, Wash. All work is now complete.
The step-up transformers for Units G-22, G-23 and G-24 are nearing the end of their useful life, and Reclamation plans to replace them within the next 10 years. The step-up transformer banks for generators G-19 and G-20 have been in continuous use since 1975. Identical transformers for G-21 were replaced in 2002 because of deteriorating conditions, and personnel recently noted the G-19 and G-20 transformers are showing signs of deterioration. An additional motive for replacing these transformers is the potential uprate of units G-19, G-20 and G-21 to 770 MW, which requires an uprate of the single phase step-up transformers from 236 MVA to 276 MVA.
The $28 million project was designed by Reclamation, and the construction phase was awarded in January 2010 to Gardner Zemke of Albuquerque, N.M., for $26 million. The project is complete.
The Units G-19, G-20 and G-21 mechanical overhaul project is in the planning phase. Reclamation has partnered with MWH Americas to investigate the potential for uprating these units, with 770 MW appearing to be achievable, depending on economics.
The planning phase for this project will be complete by September 2013, design will take place from October 2014 through September 2015, and a contractor is scheduled to be selected in 2016. The construction phase of the project is anticipated to begin in January 2018.
Chris Vick, P.E., PMP, is senior project manager with the Bureau of Reclamation, U.S. Department of the Interior, operator of the 6,809-MW Grand Coulee project.