I was watching a video about the construction of the Grand Coulee dam, and it is an impressive structure-not the least are the giant turbines, which drive generators, whoicg provide most of Las Vegas’ electricity. My question: how big can these things be made? I imagine that the enormous weight of the generator rotors would be the dominant factor-you ca only make bearings so strong. Now, we have lightweight materials-but you still must use copper wire for the rotor windings.
What are the largest hydroelectric generators today?
Three Gorges Dam has 700 MW turbines, though I’ve no idea how big they are physically. I think that’s the biggest one going.
I don’t think there’s any inherent manufacturing limit regarding the size of the bearings or any other component, but at some point it does become impractical to transport the item from the factory to the dam. The components have to fit onto a flatbed truck (even the “OVERSIZE LOAD” trucks have size limits) and be able to fit down highways and under overpass bridges and such.
Moreover, there are operational advantages to having an array of turbines/generators rather than one single large turbine/generator unit. With multiple units, one or more units can be shut down for maintenance without having to shut down power output from the entire facility.
Currently the largest hydroelectric total generation capacity in the world is at Three Gorges Dam in China. At 22.5 gigawatts, it’s over 10X the size of Hoover Dam. Whereas Hoover Dam’s turbines are about 122 MW each, TGD’s turbines provide 703 MW of power each. (dammit, phaemon beat me to it) TGD’s reservoir height is lower (607’, versus 726 feet for HD), so they must be flowing a lot more water through each turbine; that means much bigger turbines along with the 7X bigger generators.
As a point of comparison of the different technologies, Siemens produces steam turbine generators that put up to 1,900 MW and gas turbines that produce up to 375 MW. I don’t think they produce hydro turbines.
As Machine Elf suggests, transportation is going to be the primary limiting factor. A few weeks ago, the world’s largest airplane was needed to transport damaged turbine rotors from Thailand to the Siemens plant in Charlotte for repair. From the airport, it was a small traveling circus to load the mammoth parts onto trucks and drive them a few miles to the factory.
Most of the generators built here leave on rail cars. If anything, rail transport may be more restictive than trucking as trains can’t be routed to bypass narrow bridges and tunnels or low vertical clearances.
Nitpick: you are confusing Grand Coulee Dam with Hoover Dam. Hoover Dam powers Las Vegas. Grand Coulee Dam powers lots of farmers irrigation equipment, mostly, although some is shipped to California to power air conditioners.
Did you see my grandpa? He was a welder and was chosen to weld together the sections of the dam tube that Roosevelt drove through during his visit.
Your statement makes it sound as though Hoover Dam is the larger dam by electricity generation. This is false. Grand Coulee (the largest hydroelectric dam in the US) generates around 7 GW. Hoover is around 2 GW. Hoover is cooler looking, though.
I think you can move things bigger than what fits on a flatbed truck over the roads. We recently watched two big generators, each moved on a hydraulic moving machine that had about 280 separate hydraulically controlled wheels. It was a major deal, with many roads closed for hours. They removed many traffic light towers, moved overhead lines, occupied the lanes on both sides of the road, erected wooden coverings over things like traffic circles and drove over them, and similar antics. It was fascinating. Never did we see it move faster than walking speed. The hydraulic moving machines had control platforms on all corners and seemingly were each under the control of multiple people. I checked, and each generator with moving machine was over 800,000 pounds. The moving machines were 153 feet long, but the generator hung over one end. The assemblies were 24 feet high as transported. It seemed like every vehicle in the county with flashing lights got involved, and the utility companies had guys in cherry pickers managing many of the wires that they left in place across the road. First class entertainment, if you can get it.
Yeah, I know. I was being a bit facetious about what Grand Coulee Dam powers.
Here’s just the blade section of the turbine
Video on how it works.Look at how small the blade section looks in the video