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Hydro generators from Alstom are turning waterpower into electrical energy in the largest hydropower project ever built, the Three Gorges inChina, using Trelleborg's Orkot bearings.
One of the world's leading companies in hydropower generation is based at the foot of theAlps, in Grenoble, France, where hydropower was born. Casimir Brenierstarted work on hydraulic turbines in 1854 to convert the power of flowing water into electrical energy. Today, the company he founded is asubsidiary of Alstom Power and the global Technology Center for its hydropower business.
“The US still has the largest hydropower capacity, but Asia, led by China, is the fastest growing market,” says Jacques Brémond, Mechanical Engineering Supervisor at the Alstom TurbineTechnology Center. “In Europe and North America, power generation exceeds the demands of the population, while in China and India increasedcapacity is desperately needed.”
Filling the energy gap has led to the largest hydropower plant in the world, the Three Gorges on the Yangtze River, China. Alstom is supplying almost half the turbines and generators for the project. The project’s greatest challenge was its sheer size. Compare the width of the Three Gorges at 2.4 kilometersto that of a typical dam, which is around 100 meters and you begin toappreciate the scale of the undertaking.
The main part of a hydro turbine is its runner, where the water flow is converted to mechanical energy. “The external diameter of the runner for the Three Gorgeswas 23 percent larger than any other we had produced before,” says Brémond. “It was a massive 10.6 meters in diameter with a height of 5 meters.” It was impossible to produce the runners in the Alstom workshopin Grenoble. When completed they needed to be transported over the town’s bridge, but a single runner’s weight of 425 tons was greater thanthe bridge’s 300-ton weight limit.
Consequently, the runners were manufactured in a specially constructed workshop in La Ciotat in the south of France. The runners were transported by sea to Shanghai andthen transferred to riverboats. It takes six of these just to carry the draft tube elbow.
Alstom started working with Trelleborg, using its Orkot bearings, nearly 10 years ago. “We were unable to specify Orkot bearings on the left bank of the Three Gorges,” says Brémond.“We had little experience of the product at that stage and the customer requested that we design in a known solution.” To support their product, Trelleborg provided details of two independent tests on Orkot specifically for this application. “Based on these reports, we were increasingly confident about the performance of Orkot and decided to trialit in the wicket gate lower bushes during refurbishment of a Francis turbine in the Liu Jia Xia dam in China. After a few more tests in application, the product seemed successful and was first fitted in full scale on turbines supplied to the Alqueva Hydro Power Plant, Portugal commissioned in 2004,” says Brémond.
“After this experience, whenspecifying equipment for the right bank of the Three Gorges, we persuaded the customer that Orkot would be a good alternative. “The technical support we receive from Trelleborg, along with the product itself,is its greatest strength. That is why we are going to continue developing Orkot solutions for hydro generators with Trelleborg in the future.” «
In a gravity dam, the water flows down from a reservoir into a hydro turbine. It enters the runner from one side via a spiral case, which distributes the water around the turbine. A distributor withadjustable wicket gates in the turbine controls the flow of water circulating in it. The energy of the water (head and flow) transforms into mechanical energy (torque and rotational speed). This then convertsto electrical energy within the generator connected to the same shaftas the turbine. Once the water has been through the runner it goes down a draft tube back into the river.
Orkot Marine Bearings are manufactured from a synthetic composition incorporating solid lubricants for dry running to ensure outstanding wear life. Virtually no swelling in sea water and very low thermal coefficient of expansion providedimensional stability in arctic and tropical seas. They do not corrodeor promote corrosion of the housing and tolerate both edge loading and misalignment. Orkot bearings are “fish friendly”. Most metal bearings need grease to make them work properly and during operation this lubricant goes into the water. Orkot friction characteristics mean that no grease is required.
Olivier Calemard is account manager for Alstom at Busak+Shamban France, a part of Trelleborg Sealing Solutions.“Ten years ago the only products we supplied to Alstom were Orkot Wear Rings,” says Olivier Calemard. “When I first arrived at Alstom withmy ‘plastic’ bearing they laughed a little. It was so light compared to the metal ones they used; they could not believe it would be strongenough to do a good job.” Getting Alstom’s business was an uphill battle, but Calemard is certainly not one to give up. “We had to prove that Orkot could stand up to the task,” Calemard says. “Alstom would notrisk specifying an unreliable component. The cost of replacement of afailed bearing is huge. It took time and lots of independent researchand test data to convince them to use the product. Now, however, it isregularly used in the majority of their installations.”
Orkotbearings are developed and produced at the Busak+Shamban associated manufacturing company Trelleborg Sealing Systems Rotherham. They are also manufactured at Trelleborg Sealing Solutions Eugene for the American market. Due to the scale of the Three Gorges, the two sites worked together to fill the order and shared technology. “We do benchmarking of processes across the two sites,” says Barry Davies, General Managerof Trelleborg Sealing Systems Rotherham. “This is to ensure product consistency. Working on a project like Three Gorges brings this requirement right to the forefront.”
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