By Tim Brown
The 2,600-MW Chief Joseph project, at Chief Joseph Dam on the Columbia River in Washington State, is the second largest hydroelectric generating facility in the U.S. in terms of capacity. The dam and hydroelectric generation equipment are managed by the U.S. Army Corps of Engineers. The Corps selected Alstom’s Hydro business, now part of GE Renewable Energy, to rehabilitate the hydroelectric equipment in 2007.
This article examines how the Corps and GE Renewable Energy:
- Established the stringent efficiency goals for the rehabilitation project and measured its effectiveness,
- Solved technical issues during the project, and
- Enabled the plant to operate more flexibly in order to accommodate the penetration of renewable energy in the region.
Planning the rehab
Corps officials first began planning to rehabilitate the generation equipment in 2004 in order to improve the efficiency of the units. GE Renewable Energy was awarded the contract to rehabilitate the Chief Joseph equipment in 2007.
The initial scope of the project was for the plant’s 10 Newport News units, with an option for the remaining six S. Morgan Smith units. The original 16 units were brought online in the late 1950s.
Daniel Bennett, the Corps’ senior mechanical engineer at Chief Joseph Dam, said, “We conducted an exhaustive analysis and considered all the options: Should we rehabilitate the turbine runners? Should we add height to the dam to generate more electricity? Should we focus on efficiency improvement or increasing capacity? Everything was on the table.”
In the end, the Corps decided that the measuring stick for success in the project would be efficiency. Bennett said, “Testing in 2003-4 demonstrated that unit efficiency was roughly 88 to 89 percent. We knew we wanted a minimum guaranteed efficiency of 94 percent when we went out for bids in 2006.
“They came back with a guarantee higher than that, which economically penciled out quite well for us. This produced a ‘win-win’ in that while solving one problem, the team unearthed additional ways, such as the modified stay vane extensions, to improve efficiency and ultimately provide better performance.”
When the work was nearly complete, the Corps engaged an independent third-party vendor to test the efficiency of the rehabilitated units and determine if the GE Renewable Energy team had met its guarantees of efficiency levels of 95% and above.
At 2,600 MW, Chief Joseph is the second largest hydro plant in the U.S. in terms of generating capacity.
Matt Pevarnik, sales account manager for GE Renewable Energy’s Hydro business in the U.S., said, “We met the target … with 95.6% efficiency levels through a combination of improved runner design, modified wicket gate profiles and stay vane extensions. Mission accomplished.”
Bennett said he is proud of the accomplishments of the entire project team. “We’ve been able to make the repairs while still ensuring the continued smooth operation of the units,” he said. “We’ve met the higher efficiency targets, the units are operating well, they’re quiet … in so many ways we’ve met and even exceeded our objectives.”
During the preconstruction economic evaluation, it was determined that the project would produce $2 in benefits for every dollar invested, a fact that helped justify the decision. In addition, a payback for the incremental gains in efficiency and horsepower only were calculated at 19 years, assuming 94% efficiency. With the actual efficiency at 95.6%, this payback will be even sooner.
Overcoming an unanticipated problem
Like every project, this one had its challenges. For example, there was the day that Unit 11, the first unit, developed a pressure vibration that began in the turbine runner and eventually started to shake the entire powerhouse. “It pretty much shook the plant operators out of their chairs,” Bennett said.
“That’s where good partnering came back into play,” Bennett said. “GE Renewable Energy is very proactive about issues and problems. They wanted to know what it was as much as we did. Their analysis showed the problem was an ‘intermittent pressure pulsation’ caused by a ‘rope vortex’ forming underneath the runner due to water flowing through it at a rate that created an air column that looks like a tornado.”
The solution they decided to test was to get more air into the water interacting with the runner. To determine how to do that, the engineers set up a test on the second installed runner, Unit 9. “We set up an air blower system to push air in there to try and gauge how much air is needed to actually dislodge that vortex that forms,” Pevarnik said.
Through testing, the team found that they didn’t need to inject air, they just needed to make sure they could get the air to the bottom of the runner. Initially, the runner design called for a very short, truncated runner cone for maximum efficiency. However, through model testing on units where rehabilitation had not yet started, the engineers were able to model a longer runner cone that would solve the problem without sacrificing efficiency.
“Typically, longer runner cones will decrease efficiency because it starts to push air into the water column,” Bennett said. “But GE Renewable Energy was able to come up with a runner cone that had no efficiency loss while still getting the air to where it needed to be to push out that vortex.”
The role Chief Joseph plays as a peaking plant
One of the important things about the current version of Chief Joseph is its critical role in enabling the development of other renewable energy resources. This is especially important in the Pacific Northwest given the growth of wind and solar across the entire system.
“When cloud coverage occurs or the wind stops blowing, quick-responding energy resources, like Chief Joseph, are needed to ensure grid stability,” Pevarnik said. “Such stability is needed to keep the lights on, keep our computers humming, run essential facilities like hospitals and airports and so much more … all the vital services that electricity supports that we tend to take for granted.”
Bennett said, “In the past we have picked up 1,000 MWs because the wind suddenly stopped blowing. We smooth out the grid for solar and wind. Hydro is the only source that can change loads quickly and adjust for those other systems.”
With the increase of intermittent renewable energy (wind and solar) in the Pacific Northwest, the demand for grid stability is ever-increasing and Chief Joseph Dam is playing a large role, providing ancillary services such as frequency and VAR (voltage-ampere reactive) control as well as peaking power. In fact, the Chief Joseph and Grand Coulee plants are called on to meet about 45% of the region’s peaking load. Thanks to the rehabilitation project, the Corps can now provide even more ancillary services and support grid stability for the future.
In that, and many other senses, the project is evolving and adapting to the next generation of energy needs for the surrounding communities that it continues to serve.
Tim Brown is public affairs leader with GE Renewable Energy.