Bearings for tidal turbines

[Sam7000]

I came across this and have found myself curious about how it works.

http://www.openhydro.com/images.html

They build devices up to 16m diameter. As it is air-cored the bearings must be at the rim but I would have assumed it near impossible to manufacture something to the required tolerances for traditional bearings on that scale, not to mention all the issues associated with marine fouling etc.

Does anyone know anything about how they do it or how it could be done?

Thanks,
Sam

 

[MikeHalloran]

I can only conjecture.

...

Never mind that: where are they hiding the electrics and magnetics?



Mike Halloran
Pembroke Pines, FL, USA

 

[Sam7000]

I assume permanent magnets on the rotor and coils on the stator each protected from the sea by some material that doesn't impede the magnetic field

 

[MikeHalloran]

There also has to be a material that conducts the magnetic field, typically laminated iron, and there doesn't appear to be much of it present. Or maybe I am just being confused by the size of the turbine.

I'm guessing the turbine wheel has a hard track around the outside, that runs in three or more groups of bearings, each elastically mounted, or maybe the ring runs against rubber tires. The problem I have with that is that putting such a turbine in the lower Mississippi, where some kind of underwater turbines are being installed now, would result in short lifetimes for hardened parts, because that river is basically a slurry of mud.



Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

They repeatedly mention how slowly the turbine turns which is not good for generating electricity. I would assume there has to be a gearbox (perhaps more than one) in that rim which would increase the rotational velocity to drive generators much like most wind turbine have a gearbox. That rim is massive so there could be quite a lot of machinery inside. It would all have to be very well sealed to have a decent life on the seafloor.

Even slow moving turbines have to be some risk to marine life. Some species may learn to hang out on the down stream side and get fresh sushi.

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[MikeHalloran]

It wouldn't necessarily be a huge hazard to fish.

I have an ancient EE handbook that, among other things, teaches you how to build dams for hydropower. It specifiies that the intake works must involve horizontal flow to a certain maximum velocity, because fish are exquisitely sensitive to horizontal currents, and will swim away from such an intake if the velocity is not too high. Whereas a vertical intake will just suck them right in. Most reporters do not understand that the trash racks on hydro dams are for trash, not for fish.

In this case, the axial flow might cause the fish to swim upstream or laterally to avoid the increased velocity in the nozzle. If the nozzle didn't provide enough of a pressure gradient to warn the fish away, then they'd be at risk of impact by the fins, just as birds are at risk from wind turbine blades.

I'm still very curious about the bearings and seals.




Mike Halloran
Pembroke Pines, FL, USA