By Sarah Smith Bonneville Power Administration
Bonneville Power Administration 

Third Power Plant work will rebuild 3,000 tons of precision

BPA partners on overhaul of world's largest turbines

 

Even the eighth wonder of the world needs rejuvenation sometime. Trouble is, no spa will accept a 3,000-ton turbine.

That's why one of the three largest hydroelectric units in the world has been sitting in pieces on the concrete floor inside the largest dam in the nation, like a giant jigsaw puzzle that can only be solved with a 2,000-ton crane.

The mammoth water wheel, called G-24, rarely rested in its productive 33-year work life at Grand Coulee Dam in northeastern Washington, apart from pauses for an annual tune-up and a one-time rebuild of its electrical generator.

"It's been a real workhorse. We're usually running them pretty hard, and they have experienced a lot of wear and tear over the years," says Brian Clark, the Bureau of Reclamation's project manager on the overhaul of six mega-turbines in Grand Coulee's Third Power Plant.

Until last year, the turbine had worked virtually around the clock since going into operation in 1980. Made of steel, it measures 33 feet across and 18.5 feet tall. How massive are its components? It takes nuts and bolts that weigh over 900 pounds apiece to fasten them together.


Coulee Medical Center ER and Walk-In Care

"Everything's big - enormous - and the generation is unrelenting," says Scott Ross, Grand Coulee deputy power manager. Ross describes the chance to work on the world-class equipment at Grand Coulee as "a mechanical engineer's dream."

Turning at exactly 85.7 revolutions per minute, a little faster than the cadence of an average human heartbeat, the G-24 turbine transforms the implacable force of the Columbia River into the torque to generate as much as 805 megawatts of electricity. The single turbine not only produces more power than an entire coal or gas plant, its electricity is carbon-free.

Robust enough to light a city on its own, yet nimble enough to respond on a half a minute's notice to soothe fluctuations in the flow of energy across the region's transmission grid, G-24 and its five powerful siblings in Grand Coulee's Third Power Plant represent a critical asset in the operation of the 31-dam Federal Columbia River Power System.

BPA ratepayers across four Northwest states fund the refurbishments to the FCRPS power plants through their electricity rates. The work at Grand Coulee is performed by Reclamation, which owns the dam, and its contractors, with safety as the highest priority. To see an animation of the turbine being lifted and disassembled, see this video posted online .

"This mechanical overhaul is the single most important project we have going on across the system," said Michael Alder, dam operations and maintenance program manager for the Bonneville Power Administration, a federal nonprofit wholesaler of electricity.

"The Third Power Plant has tremendous value because of its size and critical position in the system. It's also been worked increasingly hard as system conditions, such as operations to protect fish and support renewables, have placed more and more demands on the plant. And there's been relatively little investment made since its construction in the 1970s."

The federal dams in the Columbia Basin supply one-third of the electricity used in the Northwest, at a cost far below other forms of energy. On top of their longstanding attributes, the hydroelectric dams have added a vital new role in recent years: balancing the output of renewable energy sources, such as wind, to fortify the transmission grid.

"Grand Coulee is relied upon to balance the needs of the regional system," says deputy power manager Eric Corbin. "Because of the unique features here, we can carry about 75 percent of the load of that balancing. It's like a big shock absorber for the system."

With 33 hydroelectric turbines spinning within a 45-story-tall dam that drains a reservoir 150 miles long, Grand Coulee produces more clean, low-cost energy than any power plant in the United States: 6,809 megawatts. At the same time, it provides voltage stabilization and balancing reserves that help keep the Northwest's transmission system reliable.

High-voltage transmission requires an exact balance between electricity supply and demand at all times. Grand Coulee and other hydro plants adjust their power output to complement and buffer the moment-to-moment variability of wind energy on the grid.

"We're like a huge, flexible backstop for the system," Corbin says. "We're able to balance all the renewables - the solar and wind - that are coming on. Our hydropower units can respond to the needs of the system faster and more efficiently than any other method we know of right now."

However, like much of the other key infrastructure in the nation, the Columbia Basin's federal hydro plants have arrived at the era of renewal. With cornerstones built before World War II, the majority of the system ranges in age from 40 to 77 years old. Although it continues to serve the region dependably, its declining condition has been exposed in recent years by more frequent and costly breakdowns.

Although G-24 is Grand Coulee's youngest unit, its 33-year track record as a heavy lifter, and corresponding state of health, made it the first of the six turbines in the Third Power Plant to be pulled out of service last year to undergo a hard-earned, two-year course of refurbishment. The base cost to renew the six turbines is estimated at $275 million, a figure that could grow if the last three turbines are upgraded to generate more efficiently.

"We're probably a little behind the curve," says Reclamation's Kerry McCalman, a power policy expert, of the Grand Coulee overhaul process. "We're starting to see some failures due to equipment that's reaching the end of its useful life. The urgency comes from the fact we've seen more forced outages indicative of the wear and tear and age of the equipment."

The two-year project to restore G-24 is part of a larger, 12- to 15-year refurbishment of the Third Power Plant, expected to cost $730 million. Having one of six mighty turbines in a plant that produces about $500 million a year in revenues out of service continuously for more than a decade represents a costly venture. But not nearly as costly as the risk of multiple units breaking down simultaneously due to age.

"We're at the point where if we wait any longer, we'd lose the benefits and ability to do it as cheaply as we can do it now," Corbin says. "It's a great re-investment for the region and the nation."

To prepare for the turbine work, the surrounding systems of the power plant needed to be strengthened and updated. Major electrical and regulation equipment was replaced, including transformers, governors, exciters and cranes. Outdated transmission cables that ran under the dam were removed and new overhead lines were designed and constructed in a $33 million project completed in 2013.

The six turbines will be removed one by one for refurbishment over the next decade. With an additional capital investment to allow the region to draw greater value from its existing infrastructure, the final three would emerge even better than new in the 2020s.

FCRPS engineers refer to this trio of turbines as the "Little Bigs" because they are slightly smaller than G-24 - producing 690 megawatts - yet more heavy duty. Turbine redesign and replacement could enable them to produce more power from the same volume of water. And that extra electricity would have the added benefit for Oregon public utilities of qualifying under the state's renewable portfolio standards, which certify new green energy sources. A final decision on this "uprate" of the last three turbines is expected in the next year.

In the case of the current project, G-24's steel turbine had retained its underlying structural integrity and the FCRPS owners and operators did not need to spring for a replacement. But decades of mechanical force, water pressure and river silt exacted punishment on its surfaces, seals and moving parts.

"The sheer dimensions and the forces on them are huge," explains McCalman, who filled in as power manager at Grand Coulee during this year's project midpoint. "Something with that much weight and power has its own wear and tear characteristics."

With an emphasis on safety, months of metal testing, sandblasting, cutting, welding, recoating and other labor-intensive efforts will restore G-24's cracked, pitted and leaky surfaces, as well as its work-weary components, to like-new condition and top efficiency by 2015. The most significant parts to be replaced are 24 wicket gates. The set of 12-foot-tall louvers are essential to regulating energy generation, opening and closing like vertical venetian blinds to control the volume of water - the fuel - into the turbine.

Despite their colossal scale, G-24's moving parts intermesh with exquisite precision. During the overhaul project, workers are machining components that weigh tons, yet must operate within clearances measured in thousandths of an inch. The reliability and longevity of the unit depend on it.

"To me, it's like a really big Swiss watch - very, very precise," says Ross.

Down in the cavernous void left behind by the turbine removal, a massive boring bar slowly pivots in a 33-foot circle. The lumbering milling machine, a million-dollar tool that was custom-built inside the dam to match the scale of G-24, has the girth and span of a large tree.

Yet its task is to delicately trim the huge metal ring until the 104-foot length is perfectly level to within a few thousandths of an inch. "Everything has to be plumb in the extreme," Corbin says.

Construction and electrical inspector Philip Lopez vets the work of the technician operating the boring bar, using a laser device to affirm that the cuts are accurate within the width of a few human hairs.

Even in the midst of perfecting the laborious details that will determine the success of a monumental project, Lopez finds that the awe of Grand Coulee never wears off. If the team does its job right, by next year, one of the three largest turbines in the world will be renewed for up to 40 more years of world-class service.

"If you've worked in other power plants, you're amazed at the magnitude of everything here," Lopez says. "I've been here for three years, and every day when I come in to work, I still go, 'Oh, my gosh.'"

 

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