Flexible gears bolster wind-turbine reliability

[krispos42]

Novel design increases torque capacity of planetary gears up to 50%.

From all outward appearances, wind turbines are sleek and elegant works of engineering. But inside, they're hell on gears and bearings. In most turbines, the rotors turn a mechanical transmission that drives a small, high-speed generator. In terms of capital investment, this is the most economical and preferred design — but large and unpredictable loads often push gearboxes beyond their limits. Downtime and unreliability are two of the main reasons electricity from wind is expensive.

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"Turbines have a giant rotor, in some cases as large in diameter as a football field, generating 1 to 2 million lb-ft of torque," explains Fox. "The gearboxes commonly have 75:1 to 100:1 step-up ratios, taking wind energy from the rotors at about 20 rpm up to 1,500 to 1,800 rpm at the generator." The trouble is, says Fox, when wind speed suddenly changes, a relatively small amount of acceleration and angular movement at the gearbox input gets multiplied 100 times at the output — building up massive amounts of torsional windup and strain energy in the gears.

<snip>

The IFB equalizes loads on planets by anchoring them onto a planetary carrier in a torsionally compliant manner. Instead of fixing the angular position of the planet gears, as is the case with conventional systems, flexible pins deflect circumferentially and independently along the carrier pitch circle — which ultimately equalizes forces on the planets, even while transmitting varying levels of torque, according to Fox.

Simply stated, external forces on the gear make "the pin bend in one direction, the sleeve bend in the opposite direction, and misalignment angle at the gear face remains virtually zero," says Fox.



Analytical models predict Timken's Flex-drives can handle 50% more torque than conventional planetary gearboxes of the same size. A version of this design has increased gearbox life six-fold in a severe wind-turbine application.

<snip>

The unit is in Scotland's Orkney Islands, a site buffeted by some of the world's most ferocious winds. Nordex had tried various windturbine gearboxes from several major manufacturers but, according to company officials and the wind-farm operators, typical life was far below expectations. The IFBs, on the other hand, successfully equalized loading, reduced internal stresses, and eliminated failures. "They've been operating since April of 2004, so we're now into the fourth year of operation," says Fox. "This accumulated service far exceeds that offered by all previous designs, and the condition of the gears and rollers is like the day they were installed.

<more>

http://machinedesign.com/ContentItem/69974/Flexiblegearsbolsterwindturbinereliability.aspx

This is wonderful news for the wind industry. More reliability means lower costs and less downtime.

[DCKit]

1. I wonder if this could lead to smaller, lighter 6-10 speed transmissions for cars?

I realize that there is no transmission on a windmill, but the same idea might allow for much smaller (read "more delicate") but more durable gears in vehicle transmissions. Just a thought.

[krispos42]

2. Luxury carmakers are already at 6-7 speeds

It will trickle down to non-luxury cars, then probably we'll be going to all-electric cars which will only need maybe three speeds tied to the electric motor. Still, more durable means less weight, which is a good thing indeed.

[skids]

3. I dunno, my personal inclination...

...is to just throw copper and magnets at the problem. Maybe gearboxes are the only way to really get the job done on the huge HAWTs, but always, always the less moving parts the better.

[phantom power]

5. They need to maintain a constant rotation rate, don't they?

Otherwise, wouldn't it make conversion to standard voltage/frequency a nightmare?

[krispos42]

6. I don't think so, but I'm not sure

I think the frequency would be set by the design of the generator. I assume it's an alternating-currenter generator, also known as an alternator. Your car has one, and converts the AC power to Dc (direct current) for your car's 12-volt system.

The voltage would probably vary with speed, as would amperage. However, assuming an alternating-current generator it would be simple and efficient to adjust the voltage to a standard level by using some sort of adjustable, reactive transformer.

Or maybe they convert it to a standard DC, then back to high-voltage AC for transmission on the power lines.

[JohnWxy]

7. this is handled by a computer adjusting the pitch of the blades.

[skids]

8. That's the "old school" way of doing it.

There are various systems that can be used to run async to the grid.

There's stuff like this:

http://en.wikipedia.org/wiki/DFIG

And these:

http://www.beaconpower.com/products/EnergyStorageSystems/SmartEnergyMatrix.htm

[phantom power]

9. DFIG. that is teh cool.

[skids]

10. teh uber cool...

...lookie what MIT made (warning PDF):

http://lees.mit.edu/lees/posters/torus_generator_poster.pdf

[phantom power]

11. Of course. A second rotor. To efficiently drive the magnetic flux.

I am a cave man.

[JohnWxy]

4. Interesting development but one quote is innaccurate:

"Downtime and unreliability are two of the main reasons electricity from wind is expensive."

Wind power is the cheapest source of electrical power today. Cheaper even than coal and it will only get even less expensive in the future as all fossil fuel sources keep climbing in price.

that said, this is a very interesting technical developement which increases wind turbine ability to cope with rapid changes in wind speed. Of course, this is handled now with computer controlled blade angle which keeps the wind gusts from speeding up the spin of the rotors.