The powerhouse for the Bureau of Reclamation’s 95-year-old, 1.5-MW Boise River Diversion facility is on the National Register of Historic Places. During a recent rehabilitation of the facility, Reclamation doubled the capacity of the plant while preserving many of the historic plant systems.
By Steven M. Jarsky and Douglas L. Miller
The U.S. Department of the Interior’s Bureau of Reclamation completed original construction of the 1.5-MW Boise River Diversion Powerplant in 1912. The plant operated virtually unchanged until 1982, when excessive operation and maintenance costs led Reclamation to place the facility in “ready reserve” status. This meant the plant could no longer operate on a full-time basis; it could operate during periods of high demand.
In the late 1990s, Reclamation added the Boise River Diversion plant, on the Boise River in Idaho, to its uprate program. The goal of this program, begun in the 1970s, was to improve operational efficiency and increase capacity at Reclamation’s 58 hydro facilities. These facilities range in size from 350 kW to 6,809 MW. Most of Reclamation’s plants have capacities of 50 MW to 200 MW, and these larger plants were the early focus of the uprate program. As demand for electricity increased, Reclamation then turned its focus to the smaller facilities.
The $6 million rehabilitation at Boise River Diversion was funded by Bonneville Power Administration (BPA). The additional electricity resulting from the rehab would help BPA meet growing power needs in southern Idaho. In addition to preserving the historic character of the powerhouse and original equipment, the modernization would more than double generating capacity of the facility.
Work on the rehabilitation began in May 2001. By June 2004, the plant was in full commercial operation, with a capacity of 3.4 MW.
Background on the plant
Construction of the Boise River Diversion Dam was completed in 1908, to deliver irrigation water to the Boise River Valley. In 1912, the 1.5-MW power plant, containing three 500-kW vertical double runner Francis turbines, was built to provide electricity for the construction of nearby Arrowrock Dam. After Arrowrock Dam was completed in 1915, the plant operated for nearly 70 years. The primary use of the electricity produced was for irrigation pumping; BPA marketed any surplus. In 1972, the dam and power plant were listed on the National Register of Historic Places by the Idaho State Historical Society.
Deciding to rehabilitate
Even when the Boise River Diversion plant was placed on ready reserve in 1982, Reclamation realized the site had potential for increased capacity. However, at the time, low power rates in the Pacific Northwest did not justify the capital expenditure to increase capacity at the site. In 1990, to further assess the options for the site, Reclamation completed a study on replacing or rehabilitating the equipment in the plant, but took no action. Eventually, the power market in the western U.S. expanded. Returns for the rehabilitation began to appear more favorable. In 2000, Reclamation stepped up its efforts to explore the potential of the site and began investigating these options in earnest. That same year, BPA approved funding to rehabilitate the plant.
Several options were investigated during those years of study. One option called for replacing the existing plant with a new 4-MW plant on the opposite bank of the river. Another option involved removing all existing equipment from the powerhouse and replacing it with new components with various single- and double-runner configurations. The third option addressed rebuilding one, two, or three units using the existing equipment configuration. The third option was determined to be the most feasible.
In May 2001, Reclamation began disassembly of the first unit at the Boise River Diversion Powerplant, to assess equipment condition and determine the extent of work needed. In December 2001, Reclamation announced its plans for rehabilitating the plant to the public, to identify any potential effects as required by the National Environmental Policy Act.
The powerhouse for the upgraded 3.4-MW Boise River Diversion plant, originally completed in 1912, is on the National Register of Historic Places. Click here to enlarge image
In February 2002, Reclamation issued specifications for the turbine-generator work at the Boise River Diversion plant. In October 2002, Reclamation awarded the contract for the work to American Hydro Corporation. Once the equipment contract was in place, efforts began to design, build, and install the three upgraded turbines and new generators, controls, and station service equipment. American Hydro began installing the new turbine runners in October 2003. In May 2004, Units 1 and 2 went on line. Unit 3 went on line in June 2004.
Designing replacement runners
Working with a vertical shaft twin runner “camelback” turbine made the re- habilitation unique. (See Figure 1 on page 44.) A camelback turbine is so named because the shape of the discharge area features two humps, like a camel’s back. Normally, these units are installed horizontally, with the humps on top. At the Boise River Diversion plant, the units were installed vertically, with the humps facing upstream.
Compared with modern vertical Francis turbines, the water passages for the Boise River Diversion units had inherently larger efficiency losses. It was important to the overall success of the rehab to understand and minimize these losses.
Designing replacement runners for the Boise River Diversion plant presented a challenge because the runner had to match the existing wheelcase geometry. Existing standard Francis runner designs are compromised when applied to the camelback configuration. This meant expanding the discharge area to lower the velocities entering the draft tube, thereby significantly reducing energy loss.
American Hydro designed the replacement runners using its computerized runner design system. This system provides an interactive design environment with complete flexibility for runner shape definition. The computational fluid dynamics (CFD) analysis provides a fully three-dimensional calculation of water velocity, pressure, and energy for the wicket gates and/or runner. The system uses boundary layer calculations to evaluate fluid losses near the surface of the blades.
Once the hydraulic design was completed, American Hydro proceeded with the mechanical design, structural analysis, and computer numerically controlled (CNC) manufacturing of the runners and turbine components.
Reconditioning the turbine casings
When reconditioning decades-old turbines, unexpected damaged and broken parts will be found. Reclamation minimized contract modifications by disassembling and inspecting the first turbine before finalizing the specifications for this work. American Hydro also inspected the powerhouse and the equipment condition before submitting its final bid for the work. As a result, only minor changes to the equipment scope and project schedule were made during the contract. An example is the modification of the electrical and mechanical interface components to accommodate the new powerhouse control system.
All but the embedded turbine components, discarded parts, and old runners were trucked to the American Hydro factory in York, Pa. The parts were cleaned, visually inspected for cracks, and, where appropriate, magnetic particle tested.
Other new components
Figure 1 on page 44 shows all the components of the new turbine-generator units. American Hydro designed and built the new packing box support to allow access under the generator to service the turbine shaft seal. Self-lubricating bearings from Orkot were installed. All opposing surfaces were made of stainless steel for the wicket gate shift rings, shaft bearings, wicket gate linkages, and gate shaft pillow block bushings.
Each of the three turbines has 32 wicket gates. The initial disassembly by Reclamation revealed damage to about one-third of the total number of gates. Therefore, specifications required furnishing new gates for one unit and rebuilding the best of the remaining gates for the other two units. All the new gates were installed in Unit 3, while Units 1 and 2 received reconditioned gates. American Hydro machined the reconditioned gates on the bushing bores, leaf ends, and vertical seals for realignment. A shallow counterbore for locating self-lubricating washers was machined into the upper and lower leaf ends. New lower cover plates,base plates, and distance pieces were manufactured to maintain alignment and structural integrity of the turbine assembly.
After machining, interface surfaces for both new and refurbished wheelcase components were assembled in the shop.
Replacing mechanical governors with digital
The new governing system, supplied by L&S Electric, Inc., includes digital governor modules, hydraulic power units, hydraulic actuators, and piping. The governor is a “speed droop” type, using gate position feedback for secondary control. The digital modules use solid-state programmable logic controllers (PLCs) with standard off-the-shelf components. The failsafe design monitors critical control signals that are programmed to take corrective action (switching to an alternate mode of operating or failsafe shutdown mode) and annunciate any failure.
Redundant power converters for the digital governors include a primary 125 volts direct current (DC) from the existing station battery system and a secondary 24 volts DC control. All start, stop, indication, and alarm functions are displayed on the graphical operator interface. The operator station’s control/indication unit has user-configurable screens.
Figure 1: New equipment installed during rehabilitation of the Boise River Diversion plant included generators, turbine runners and shafts, balance piping, self-lubricating bearing blocks, and cover plates. Click here to enlarge image
The hydraulic power units operate between 1,180 pounds per square inch (psi) and 1,600 psi. They feature a lead/lag alternating current-driven pumping system, duplex filtration system, bladder-type accumulators, switches, gauges, and valving. Wicket gate closing times are adjustable between eight and 20 seconds.
Reinstalling the turbines
Installation of the turbine and generator at the Boise River Diversion plant required ingenuity and planning. All the major components had to be brought through narrowaccess hatches from the loadingdock, across the original main operating floor, anddown through the existing stator bore. In addition, concern about capacity of the overhead crane limited all lifts to only 6 tons. This required disassembly of the major components of the generators and turbines after factory fitting and testing, then reassembling them on site as the unit was stacked from the bottom up.
First, new foundation and adapter plates were installed on the lowest level, after being aligned with the generator support ring centerline. Next, the downstream portion of the camelback discharge piece was mounted on the lower distributor and base ring. Then the 25-foot-long turbine shaft with both runners mounted on it had to be lifted from the loading area, through a small hatch in the main operating floor, and lowered into position. Finally, the upper distributor, draft tube make-up piece, and turbine completion parts were installed.
Installing new generators
Installing a higher-speed turbine runner opened up the possibility of installing a completely new generator on the thrust deck floor, below the existing generator. American Hydro investigated several designs before choosing a vertical synchronous generator supplied by General Electric. The totally enclosed air-to-water cooled generator runs at 240 revolutions per minute (rpm), 1,150 kilovolt amperes. The overall dimensions of the new generator just fit into the room between the main operating floor (elevation 2827.8 feet) and the lower floor (elevation 2818.8 feet). New air, water, and cable passageways were made to accommodate the control, governor, switchgear, and other equipment in adjacent areas. The original generator rotor had to be removed because the top of the new exciter extended about 18 inches up into the original stator. With the stator and covers reassembled, the old generator maintains its original appearance.
The generator is designed for 90 degrees Celsius temperature rise with Class F insulation. The stator winding used is epoxy mica insulation that was vacuum pressure impregnated at the point of manufacture. The generator has a combined upper thrust and guide bearing using self-equalizing tilting pads and a hydrostatic lift pump assembly for start-up conditions. Both the upper and lower bearings are mounted in an oil sump that eliminates the need for an oil circulating system.
The generator was too big and heavy to be lifted in one piece. The coolers, stator, and rotor components were assembled piece-by-piece on site. The new generator support was installed before lowering the stator into position. The final alignment involved four bearings along a 33-foot shaft length.
Revitalization and upgrading of older hydro generating facilities can provide significant electricity increases from domestic renewable resources. The Boise River Diversion rehabilitation brought back into production a facility that had been in ready reserve status for more than 20 years. The original plant capacity was doubled by using modern turbine technology, without any significant structural changes.
From early in the project, Reclamation decided to retain as much of the original equipment as possible to preserve the historic qualities of the Boise River Diversion plant. Today, all equipment within the main operating floor, although no longer in operation, remains visually as it was in 1912. The overhead crane is still operated manually from its pendant chains, the old slate plant control boards with open knife switch disconnects and indoor step-up transformers are still in place (although no longer energized), and the original upper generator components were put back in place over the new equipment.
Through the rehabilitation process for the Boise River Diversion plant, Reclamation personnel learned several valuable lessons:
To retain the historic characteristics of the 3.4-MW Boise River Diversion powerhouse, the U.S. Department of the Interior’s Bureau of Reclamation replaced the old upper generator components over the new equipment. Click here to enlarge image
– Encouraging equipment suppliers to offer alternative solutions was critical to the success of the project. The initial requirement to rebuild the existing generator windings proved difficult for prospective bidders to assess, and initial bids exceeded the available budget. Subsequent flexibility in the specifications led to the creative solution of in- stalling new generators while leaving the visible parts of the old generators in place.
– Because the configuration of existing facilities limits the scope of an upgrade, it is important to understand critical aspects before issuing specifications. The capacity of the overhead crane at the Boise River Diversion plant was only 6 tons, and available space was limited. Equipment designs were modified to accommodate these limitations, rather than adding costs to upgrade plant auxiliary equipment to handle heavier lifts and modifying the plant structure to meet large space requirements.
– A thorough understanding of historical operating procedures is critical when rebuilding older facilities. In this case, the equipment sat idle for many years, and experienced operating personnel were no longer available.
After the units were put into commercial operation, Reclamation discovered that, at low flow, there was an insufficient volume of water to fill the draft tube chamber to initiate a siphon effect. When the draft tube cannot recover the energy discharged from the runners, turbine performance deteriorates. During low flow operations, the plant crew must manually install adjustable weir gates downstream from the draft tube to keep the water level backed up into the draft tube. Slots for these weir gates were installed at some point in the plant’s history, but the need for this feature was not documented in the operating history of the plant and was not fully understood until commissioning of the new equipment. Luckily, most of the weir gates were discovered in the scrap yard at the site, and only a few had to be manufactured by Reclamation crews.
– Disassembly of one unit by in-house forces provided several benefits. First, it allowed for more accurate specifications and let prospective bidders inspect equipment condition. This resulted in very few modifications during the term of the contract. Care was taken to document the “as-found” conditions for the specifications and for future reference during assembly.
Second, it allowed Reclamation to make the necessary repairs to the crane before the contractor began working.
Third, it revealed an unusual feature of the plant. While preparing the specifications, Reclamation performed a historical document review. Photographs showed the concrete walls of the powerhouse being constructed after the turbines and generators were assembled. This explained the small access hatch in the plant. No record was found of the units being disassembled since original construction in 1912, and plant crews doubted whether the components would fit through the hatch. Before disassembly began, Reclamation crews made a “mock-up” model of the hatch and major components. This exercise revealed that major components would have to be rigged horizontally to fit through the hatch. Even then, there was only an inch of clearance to get the components out of the building. The model saved much “trial by error” frustration of rigging and lifting.
– Historical records describing the original procedure for shaft alignment and bearing clearances are valuable. None could be found for this situation. Shaft alignment proved to be difficult because of the inaccessibility of the long vertical double-runner turbine shaft encased in its “camelback” housing. Methods used for aligning standard hydro turbines had to be modified and required some degree of approximation. To aid the alignment procedure, proximity probes were installed at the upper and lower turbine bearings to monitor runout during operation. This has resulted in the fine-tuning of bearing alignment and clearances to keep bearing runout and unit vibration within industry standards.
– The rehabilitation entailed three separate contracts, with significant interconnection work by Reclamation plant crews. One contract was for the turbine, generator, and governor systems; one for the switchyard, switchgear, and station service systems; and one for the plant control system. Plant crews coordinated work with the three contractors and were responsible for interconnections among all the supplied equipment, installation of the auxiliary systems, and overall plant commissioning. Having a knowledgeable plant crew on site was very helpful to the contractors and instrumental in making the project a success.
Mr. Jarsky may be reached at Bureau of Reclamation, Pacific Northwest Regional Office, 1150 North Curtis Road, Suite 100, Boise, ID 83706; (1) 208-378-5300; E-mail: [email protected] Mr. Miller may be reached at American Hydro Corporation, P.O. Box 3628, 135 Stonewood Road, York, PA 17402; (1) 717-755-5300; E-mail: [email protected]
Steve Jarsky is deputy manager, Resource and Technical Services, for the Pacific Northwest Region of the U.S. Department of the Interior’s Bureau of Reclamation. He served as Reclamation’s project manager during the rehabilitation. Doug Miller, P.E., is manager, international and government sales, with American Hydro Corporation. For modernization of Boise River Diversion, he coordinated the preliminary engineering and final design options for the turbine, generator, and governor.