Rehabilitation of the ten turbine-generating units in Powerhouse 1 at the 1,076-MW Bonneville Dam project involved unique constraints and challenges. The U.S. Army Corps of Engineers partnered with contractor Voith Hydro to design solutions to these challenges that allowed for successful, cost-effective completion of the rehabilitation.
By James R. Mahar and Mark E. Kennell
The effort required to successfully manage the rehabilitation of a large hydropower facility is complex even under the simplest set of operating conditions. When factors such as aging infrastructure, inconsistencies in previous design and construction practices, fish passage, and basin regulation are added to the mix, an effective working partnership between the operating agency and contractor is essential for success.
The collaboration between the U.S. Army Corps of Engineers and Voith Hydro proved to be the most effective tool in overcoming many difficult challenges during rehab of the 1,076-MW Bonneville Dam project. The rehabilitation was completed in July 2010. Total cost was $155 million over a 14-year period.
Bonneville Lock and Dam
Development of Bonneville Lock and Dam began with the Rivers and Harbors Act of 1925, when Congress ordered the Corps to identify potential sources of hydroelectric power across the U.S. Construction of Bonneville's infrastructure began in 1934 and culminated in a ten-unit hydro powerhouse, a deep-draft navigation lock, two adult fish ladders, a juvenile fish bypass system, and a spillway. In the fall of 1937, President Franklin D. Roosevelt dedicated the first two generating units, each with a capacity of 54 MW. The Corps installed eight additional units by 1943.
Soon after hydroelectric power became available to the public in the northwestern U.S., the Bonneville Project Act of 1937 authorized the Bonneville Power Administration (BPA), the power marketing agency, to market the sale and transmission of this energy.
Today, Bonneville Lock and Dam features:
- Two powerhouses containing 20 Kaplan turbines with a total capacity of 1,076 MW;
- Four adult fish ladders rising 60 feet;
- Two independent juvenile fish bypass systems;
- An 18-bay concrete gravity spillway that can discharge 1.8 million cubic feet per second (cfs);
- A shallow-draft lock; and
- A significant recreation and visitors program.
As a run-of-river project, Bonneville does not contribute significantly to flood damage risk reduction or irrigation.
In 1992, Congress, through the National Energy Policy Act, authorized the secretaries of the Army and Interior to accept funding provided directly from BPA, in lieu of annual Congressional appropriations. As a result, funding received from BPA was directly applied toward the operations, maintenance, and capital programs at the federal facilities within the Federal Columbia River Power System (FCRPS). The FCRPS consists of Corps and Bureau of Reclamation hydro projects in Washington, Oregon, Idaho, and Montana.
Rehabilitating, modernizing Bonneville
More than 70 years have passed since Bonneville Lock and Dam was dedicated in 1937. During this time, the power-train infrastructure underwent numerous additions and modifications. In 1994, Voith Hydro, under contract with the Corps, began a comprehensive rehabilitation and modernization of the aging 518-MW Powerhouse 1. The rehabilitation task, including minimizing electrical and mechanical anomalies created by past construction efforts, proved daunting, especially considering the added constraints of a facility steeped with environmental concerns.
For the Bonneville rehab project, Voith Hydro offered the Corps a comprehensive project solution, with worldwide resources through a network of engineering, manufacturing, and service organizations. This – coupled with Voith Hydro's skill in optimized project planning and execution – assured the Corps a high level of quality.1
Voith Hydro also offered performance-based total solutions to ensure both technical and financial success. By single-sourcing with Voith Hydro, the Corps eliminated the time-consuming and typically inefficient management of multiple suppliers and shortened the project schedule.
Together, Voith Hydro, as the primary contractor, and the Corps' quality assurance and construction representatives completed a major rehabilitation and modernization of the Bonneville Lock and Dam First Powerhouse. In July 2010, rehabilitation of the last of the ten units was complete.
While the rehabilitation assured the continued dependability of the power-train equipment, the modernization effort optimized the use of water and helped to meet emerging reliability compliance regulations. The scope of work included the design, manufacture, installation, testing, and commissioning of the following components of the ten main generating units:
- Fish-friendly 280-inch-diameter adjustable Kaplan runner;
- New fish-friendly (minimal gap design) bottom ring and discharge ring;
- Completely restacked and rewound stators;
- Refurbished wicket gate and blade operating mechanisms;
- Refurbished main shaft bearing systems;
- Addition of environmentally friendly self-lubricated wicket gate mechanism bearings; and
- Refurbishment and testing of the existing generator rotor.
|Personnel at Powerhouse 1 of the 1,076-MW Bonneville Dam project celebrate installation of the last of the ten turbines replaced during the recently completed unit rehabilitation.|
Constraints unrelated to power generation
The Columbia River is the second largest waterway in the U.S. and is second only to the Mississippi River system in flow and navigation commerce. The Columbia River Basin also delivers the lion's share of the hydropower produced in the U.S. As such, conditions not normally encountered in a typical plant rehabilitation were, in some cases, one of a kind at Bonneville. These included fish passage considerations, management of multi-state environmental regulations, regional basin regulation requirements, changes to the way the rehab was funded, and a requirement to protect an historic building.
Fish passage considerations
Passing anadromous fish through a hydropower facility is atypical for most North American projects. However, at the majority of Columbia Basin hydropower facilities, fish passage is probably the most scrutinized, criticized, and debated program. Therefore, critical path schedules included fish passage operations in terms of scheduled outages, availability of priority units, and dissolved gas capacity to meet the regional water quality standard.
Management of multi-state environmental regulations
Bonneville Lock and Dam is essentially a 2-mile span across the river between Washington and Oregon. Although Powerhouse 1 is entirely in Oregon, Voith Hydro had to transport and store equipment elsewhere due to space limitations. Thus, environmental practices, including the proper accounting of hazardous waste, required management under differing state regulations.
Regional basin regulation
Flow regulation for the Columbia Basin system involves four U.S. states and another country (Canada). Stakeholder interests include hydropower, fish survival, flood risk damage reduction, irrigation, water quality (dissolved gas), navigation, and recreation. Further complicating the act of balancing flow are low water years. Other unpredictable circumstances include pollutants entering the river from various sources, local community disaster assistance, and the unscheduled repair of aging infrastructure.
To meet the multiple demands for water use, the northwestern U.S. mainstem river systems are regulated by the Corps' Reservoir Control Center. Thus, changes to system regulation and flow (in terms of unit availability) had to be considered regionally during the rehabilitation.
Changes in funding for the rehab
At the start, the work was solely funded by Congress with appropriated dollars. However, as direct funding from BPA became available through capital investment programs, a transition over several years took place. This transition to a direct-funded capital program proved cumbersome at first. Although accounting principles remained consistent, the application of process proved disruptive until the process of receiving funds and paying contractors was resolved.
Protection of an historic building
Powerhouse 1 is included in Bonneville Lock and Dam's placement on the National Register of Historic Places. The Bonneville project became a Historic District in June 1986. This listing requires that modifications to the interior of the structure be coordinated with the State Historic Preservation Office.
To combat damage to vintage material, the floors and lower walls of the interior were covered and protected before rehabilitation began. A video survey was conducted prior to work beginning to ensure any damaged areas could be restored to their original condition. The demobilization process included damage repair consistent with the original design and materials used.
|The generator stators were restacked and rewound during the rehabilitation of the ten units in Powerhouse 1 at the 1,076-MW Bonneville Dam project.|
Finding solutions for power-related challenges
In addition to the non-power considerations described above, the Corps and Voith Hydro faced several power-related challenges during the Bonneville rehab. Solutions to these challenges included designing a "fish-friendly" turbine runner, coping with lack of drawings and differences in unit design, overcoming schedule acceleration and logistical challenges, discovering and fixing worn wear plates, refining the line boring process, and solving electrical phase configuration inconsistencies.
Fish-friendly runner design
Increasing the survival rates of juvenile salmonids passing through the powerhouse while on their journey toward the Pacific Ocean was a key goal of the rehabilitation. Voith Hydro patented significant portions of a fish-friendly Kaplan runner manufactured and installed at Bonneville. Use of this turbine has increased fish survivability from about 97 percent to 98 percent. This 1 percent improvement justifies the financial investment.
Although there were some design characteristics already in existence at the Corps' Truman Dam in Missouri, the Voith Hydro minimum gap runner turbine design was the first generation of this type of Kaplan runner.
In addition, Voith Hydro reshaped the turbine's discharge ring and changed its placement when positioning the runner. This reshaping was needed to accommodate the tighter tolerance and more rounded shape of the blade tips when fitted into the discharge rings. This further reduced the gaps present with the replaced blades. The concrete-embedded steel supporting the original discharge ring was machined to accommodate the new spherical shape.
Also, because the upper edge on the new discharge ring is spherical, the ring could not be installed prior to the turbine runner installation. Rather, the ring had to be lowered with the turbine between the blades and intermediate head cover assembly. Once the runner was positioned in place, the spherical discharge ring was staged in a temporary position, then lowered toward the blades and eventually pressed and fastened into its permanent position.
In addition to improving juvenile, adult fallback, and kelt passage, minimizing the gaps between the blades and inner cone and outer discharge ring reduced water loss, turbulence, and pressure, and ultimately increased unit efficiency. This gained efficiency allows for the generation of more power from the same amount of water. Also, after extensive empirical testing, which confirmed improved juvenile fish passage survival, the fish screens located at the three intake slots for each unit and used to direct fish away from turbines 2 through 9 were removed, as they were no longer necessary. Removal of these screens reduced labor-intensive maintenance and eliminated the need to procure expensive parts for the fish screens. This resulted in thousands of dollars in annual savings for the Corps. Also, eliminating the requirement for fish screens to be in place and functional before a generating unit is brought on-line reduced the rate of forced outages by a small percentage.
Coping with lack of drawings and differences in unit design
Before the rehabilitation, the main generating units had never been fully disassembled since their original installation, dating back as much as 50 years. Assuming legible, accurate as-built drawings or even that a drawing existed when needed would have been a mistake.
The differences between Units 1 and 2 and Units 3 through 10 complicated the issue. The first two units were different in various dimensional parameters; what was discovered and corrected from poor drawings for these two units had to be rediscovered and corrected for the remaining eight.
The most challenging of the differences between the two families of units proved to be the rotating shaft system (guide bearings) and stator size. Each required a complete set of drawing modifications, including dimension verification. Frequently, while parts were disassembled, an alteration in process, such as a rigging technique or electrical adjustment, was made "on-the-fly." The challenges were addressed by a careful catalog review and drawing update process, coupled with an inspection of each individual component as it was removed in preparation for its rehabilitation. The final product included a single set of drawings combined from the original two, which is now representative of as-built conditions.
|The generator rotors underwent a general refurbishment and testing during rehabilitation of the ten units in Powerhouse 1 at 1,076-MW Bonneville Dam.|
Overcoming schedule acceleration and logistical challenges
In 2007, Voith Hydro proceeded to accelerate the schedule to complete the base contract activities ahead of the original completion date. To Voith Hydro management, time is money. To the FCRPS stakeholders, "power" is money, so the accelerated schedule benefited both organizations.
The accelerated schedule meant that, on occasion, three units would be out of service at the same time. The logistical challenges required innovative methods to inventory, locate, and retrieve the various unit components. Specifically the rotors, bearing brackets, outer head covers, and runner assemblies from multiple units had to be stored in such a way as to ensure an efficient first-in, first-out retrieval process.
In the spirit of partnership, the Corps made additional floor space available and approved the placement of various components in stacks of two or three. Another tactic was to straddle larger components over smaller ones. Both tactics were designed to make more efficient use of the available space, though often in an unorthodox manner. With this, safety concerns increased, so Voith Hydro and the Corps engineered infrastructure supports, developed a new activity hazard analysis for rigging operations, and mounted additional fall protection devices where needed.
To meet the new completion date, emphasis turned from Unit 1 to Unit 3. That focus was maintained and the projected completion date was slightly ahead of schedule.
Discovering, fixing worn wear plates
The wear plates above and below the wicket gates on Units 3 through 10 are made of copper instead of the steel found in many other units. Voith Hydro discovered that the soft copper was more worn than expected, and ripples, due to unevenness, were exposed once the wicket gates were removed. These worn, uneven surfaces presented a problem: the end clearance between the plates and top and bottom of the wicket gates had to meet a tight tolerance specification.
To solve this problem, Voith Hydro built up the wicket gate ends so that each gate was milled to the exact same size. Wear plates then had to be smoothed and ground to accommodate the built-up wicket gates. Initially, Peak Hydro (formerly Weld Mart) hand-ground the wear plates, but after consultation with the Corps' quality control representative switched to a machining process. This offered a better product for the Corps and proved economical for Voith Hydro even though the machining gear device and process were not in the original procurement plan. The resulting product met specification and greatly reduced leaking when a unit is off-line and the wicket gates are on-squeeze.
Refining the line boring process
The distance the line boring milling bit head had to travel from the top of the upper head cover to the bottom throat ring was about 12 feet. The head cover and throat ring enclosed one wicket gate bushing each, and a third bushing centered the rocker arm. The process of boring the three bushings was first accomplished with a single steel bar holding the milling heads in place. The specified tolerance is a tight 0.002 bore, requiring a nearly vibration-free environment. The length of the bore and the difficulty of taking adjacent units off-line made the line boring a process improvement learning curve. A requirement in the fish passage plan to keep specific units on-line for attraction water complicated the issue. At times, adjacent units could not be taken off-line, thereby preventing line boring from proceeding due to vibration.
As a solution, Voith Hydro and the Corps refined the process of boring the upper head cover and throat ring separately. Initially, Peak Hydro used laser guides to address the obvious problem of maintaining the transfer concentricity over a 10-foot distance. However, the final technique to achieve accuracy of alignment between these sets of bores involved a combination of plumb wire and a precision digital level. The project team mastered the new trial-and-error process over the course of the rehab, boring two units when the wicket gate stems aligned to specification. Voith Hydro reports this method is now a standard practice.
Solving electrical phase configuration inconsistencies
Units 1 and 2, installed nine years before the last eight, were wound and connected to a C-B-A delta bus. The last eight were connected to a different A-B-C delta. When Unit 1 was placed back in service after its rehab, it was wound to the now A-B-C standard as specified for consistency within the powerhouse. Because Unit 1 is used for fish attraction water, it had to be brought on-line before Unit 2 was taken off-line. As such, the phase connections on the delta bus required reconfiguring to accommodate for the interim difference between the C-B-A and A-B-C wound units, respectively. Once Unit 2 was completed, all units were configured consistently after the interim fix was reversed.
After many years of cooperation between the Corps and Voith Hydro, the rehabilitation of Powerhouse 1 was completed in July 2010. At that time, the powerhouse was returned to a fully operational facility. The success of this project is measured in meeting the contract specification within budget and schedule.
It would not have been possible to meet the expectations or mission requirements of both the Corps and Voith Hydro without good communication, idea sharing, and trust. The key to the rehabilitation's success was the partnership between the owner and equipment contractor and the joint development of realistic goals to meet each other's expectations. Continual communication with stakeholders regarding work plan progress or anticipated changes, especially considering the unique nature of this rehab, proved difficult but essential as conditions stressed schedules and budgets.
Of significant importance, especially because Bonneville's Powerhouse 1 is the first dam from the Pacific Ocean inland on the Columbia River, is the improved juvenile fish passage through the turbines. The improvement taxed the rehabilitation process but was significant enough that regional experts agree: passing juvenile salmon through the units protects fish better than the conventional screened intake and bypass system.
1Voith Hydro has installed more than 40,000 turbines and generators, with total capacities of more than 300,000 MW worldwide.
Jim Mahar is chief of operations, Portland District, for the U.S. Army Corps of Engineers. He was responsible for daily operations and maintenance of the Bonneville facility. Mark Kennell, director of field operations for Voith Hydro, supervised the company's on-site project manager.