Go with the flow14 September 2004
With the current 50-year Priest Rapids operating license set to expire in October 2005, Grant PUD has led an extensive process to obtain a new FERC license that includes support for the installation of a new turbine design, writes Kathy Kiefer
GRANT COUNTY in eastern Washington state is situated at the heart of the Columbia basin irrigation project, one of the US government’s largest reclamation projects. Public Utility District No. 2 of Grant County (Grant PUD) owns and operates the Priest Rapids project, which consists of two hydroelectric developments on the Columbia river; Wanapum and Priest Rapids. Created by a vote of the people of the county in 1938, Grant PUD is the sole provider of power to this rural area.
In 1955 the Federal Power Commission, now the Federal Energy Regulatory Commission, (FERC) issued Grant PUD a 50-year license to construct and operate the Priest Rapids project.
Wanapum, the most upstream dam within the project, began generating power in 1963. The power house contains 10 Dominion Engineering Works Kaplan turbines rated at 120,000 horsepower each. Over the last 10 years, turbines at Wanapum dam have begun to show signs of accelerated wear and deterioration while maintenance costs have increased.
There are 12 salmon and steelhead species in the Pacific Northwest’s Columbia/Snake river system listed under the Federal Endangered Species Act (ESA). Over the last 20 years, Columbia river hydro power operators have managed projects with increasing regulatory requirements and laws that require operators to improve the survival of ESA listed species.
The national-hydropower-association Research and Development (R&D) Committee developed and promoted a plan to seek support for a turbine that would improve operational efficiency for different hydro power operators. The goal was to address problems with power generation efficiency, fish survival, water quality and turbine maintenance.
Battling the perception that hydroelectric technology was mature and not eligible for research and development funding, the R&D group went to the US Department of Energy (US DOE) to seek funding for the new turbine design.
Ten hydro power participants, including Grant PUD, each offered US$50,000 and the US DOE provided matching funds, kicking off US DOE’s Advanced Hydropower Turbine System (AHTS) programme. The mission of the AHTS is to develop technology that will maximise the country’s hydro power generation while minimising adverse environmental effects. The goal is to develop turbines that allow 98% survival of passed fish. After the first year of funding, the US Congress appropriated US$2M, increasing to US$5M the following year and currently averages US$7M a year.
Grant PUD commitment
Over the last 25 years, Grant PUD has conducted over 150 different studies to learn about salmon behaviour in the project area. Over US$40M has been invested on structural modifications to the power house intended to improve salmon survival.
Grant PUD currently spills an average of 50% of the river flow at the Priest Rapids project facilities to move juvenile salmon down river during spring and summer migrations.
New technology has been developed to quantify specific causes of mortality as juvenile salmon pass through turbines. At Wanapum dam, nearly 70% of the juvenile salmon use the turbine passage route. Overall dam passage survival at Wanapum ranged from a low of nearly 88% in 2001 to a high of 97% in 2003.
In response to these findings, Grant PUD engineers and biologists investigated solutions that would improve equipment performance and fish survival. Grant PUD participated in jointly funded efforts with US DOE to evaluate advanced design turbines. Competitive model testing took two years. Models of the project from the intake through the draft tube were built on a 1:20 scale. Data acquired from the studies were used as the basis for specific improvements to the design of turbine components. The new design addresses the entire hydraulic passageway with the goal of developing a turbine that is more efficient, less turbulent, with zero cavitation and that improves fish survival.
Brad Strickler, Grant PUD’s lead engineer for the project noted: ‘This is a state-of-the-art turbine. It incorporates everything that the US hydro industry currently knows about fish passage through turbines. The design includes the modification of turbine parts that might damage fish and incorporates a new runner, a new shaft, bearing, inner and outer head covers, wicket gates, bottom ring, discharge ring and upper draft tube liner. Parts that demonstrated cavitation problems are being replaced with stainless steel. This is the first time this has been done in the industry.’
With the 50-year operating license set to expire in October 2005, Grant PUD has led an extensive process to obtain a new operating license from FERC that includes support for the new turbine design installation. Advanced turbine work is also supported by federal and state resource agencies with regulatory jurisdiction over the effects of the project on anadromous fish.
The geometry of the new runner assembly will change the flow dynamics to reduce sheer below the tolerance threshold acceptable to juvenile salmon passing through the turbine. The new turbine has six smaller blades instead of five on the existing Kaplan turbine. The new runner reduces the pressure-versus-time and the velocity-versus-distance gradients while minimising clearances between the runner and the discharge ring, and maximising the volume of flow passage. The servomotors that move the blades will be located near the top of the turbine shaft instead of at the hub.
The new turbine will have 32 wicket gates instead of 20 and every other gate will be aligned with one of the 16 stay vanes. The new blade centre line will be lowered. The new turbine is expected to produce an overall efficiency gain of around 3% and an overall capacity gain of 15%.
The new turbine goes on line in February 2005, in time for testing at the outset of the spring juvenile salmon migration. With nine additional turbine units planned for replacement at Wanapum dam, there is a lot at stake as this major undertaking unfolds.
Communication and coordination between voith-siemens Hydro Power Generation’s engineers and Grant PUD field operations staff, engineers, inspectors and mechanics has been a major part of the success of the programme. With turbine parts cast in Sao Paulo, Brazil and the turbine shaft and other parts forged in Bucharest, Romania and Ljublana, Slovenia, the inspection work alone has been a monumental task.
The turbine shaft, weighing in at 80t, left the Black Sea Port of Constanta in August, bound for Houston, Texas. All runner parts were received at Voith Siemens Hydro’s, York, Pennsylvania plant, assembled then disassembled for transport to Washington state.
On-site removal of embedded parts and draft tube modifications have continued ahead of schedule while parts begin to arrive at the plant. Assembly of the turbine generator unit begins this October with the unit start-up scheduled for next February.
Kathy Kiefer is public affairs officer for Grant PUD