The Cellar - June 21, 2010: Flaming Fans

The Cellar (http://cellar.org/index.php)

- Image of the Day (http://cellar.org/forumdisplay.php?f=10)

- - June 21, 2010: Flaming Fans (http://cellar.org/showthread.php?t=22991)

Quote:

Originally Posted by classicman (Post 664983)

I think I posted this before - or someone else did.
At least this one didn't catch fire. Dunno where those blades flew off to though :eek

I read something about them having difficulty with high winds. They have brake systems which overheat or something??? Maybe its the gearboxes to which Bruce is referring.

The first film looks like it was hit by an artillary shell. The windmills I studied in the eighties had a feathering mechanism that kicked in if the RPMs got too high.

Or it could be this ...

Quote:

Chain of events

• Vestas state that service was requested for the turbine, following a malfunction of the brakes (cause: worn brake). At the last routine major checkup it was noticed that the main gear made some noise. It was then recommended to have an endoscopic inspection done and a price quote was forwarded.

• A service team from Vestas arrive Friday morning to check the brakes. The brakes were repaired and checked.

• The braking mechanism is tested eight to ten times from the nacelle [engine house on top of the tower]. Then the turbine is restarted from the bottom of the tower with the intent of putting it back into normal production. At this point, the wind is very strong. The airbrakes at the tip of the blades are used to control the speed of the rotor, prior to attaining operational speed, according to Vestas. That means the tips of the blades are turned out during the start.

• During the start of the turbine, just when it is put back on the grid, noise is heard from the nacelle. The service personnel press the stop button. The turbine’s control system starts a controlled shutdown procedure, but a large crash is then heard (probably the gear that fails). The turbine is shaking strongly and cable assemblies, etc., fall down inside the tower. The rotor stops abruptly for a moment, but then starts turning again. The speed of the rotor is rather low, but it is noted that the turbine no longer can be controlled from the control panel and stopped by the brake on the high-speed axle. The personnel evacuates the tower immediately. Outside, it is observed that the airbrakes at the tip of the blades have broken off.

• The wind is very strong. The turbine continues to gain speed, and attains speed beyond its design limit.

• The service personnel contacts the local police and assist in establishing a safety zone of 400 meters (1300 feet) and warn the neighbors. This continues for 21/2 hours.

• The turbine wrecks. The events are filmed by a neighbor and later shown on the TV2 station. The result is that the blades collapse, the tower is hit and is strongly indented. The nacelle is bent forwards (against wind direction). Pieces of all three blades are thrown a great distance downwind from the tower, almost 180 degrees.

• The nacelle and the upper part of the tower falls to the ground in front of the tower. The generator falls out and rests next to it.

• Large pieces of the blades land 200–300 meters (600–900 ft) away, while small pieces appear to have flown 500 meters (1600 ft). Smaller, lighter pieces are found near a farmhouse, about 700 meters (2200 ft) away, though these may have landed and then been blown further by the wind, as the wind was very strong.

• The lower part of the tower remains standing. An inspection of the gear shows it to be damaged.

• Nobody was hurt.

Link

ETA - Bruce was right , again.

I think that the turbines in post #7 are both older, and fairly small. A modern wind turbine rotates at 10 to 20 RPM, and those in the videos look like they're going quite a bit faster.

Of course, they're also on fire.

A buddy of mine photographed the construction of the blades. You can stand up inside them when they are laying down.

Quote:

Originally Posted by spudcon (Post 665169)

The first film looks like it was hit by an artillary shell. The windmills I studied in the eighties had a feathering mechanism that kicked in if the RPMs got too high.

looks like the blade flexed and bashed into the tower.

The top right and bottom left turbines are, I think, the same as in post 7 & IIRC the bottom left in post 1 is the same exact turbine.

As for the rest I've no clue how old who made or anything else. From what limited reading I did today, the problem remains the same under abnormally high winds that are sustained for a length of time. The brakes/gearboxes overheat and fail.

probably Chinese made gearboxes...

How frigging hard can it be to make a gearbox that doesn't blow up? I think even GM can do that.

The gear boxes on the big turbines are like nothing else. I used to work for one of the labs that did fatigue testing on them and they were having a lot of trouble finding test equipment that was stronger than the gear boxes.

Regarding the blades striking the tower, part of the problem is that most of the turbines currently being manufactured are upwind turbines. When the wind blows it flexes the blades toward the tower. Downwind turbines don't have that problem, but they do have what's called "tower shadow." Every time the blades pass behind the tower they enter an area where the wind is blocked by the tower. This causes a cyclic loading on the blades, which contributes to fatigue failure and an increase in noise.

So is it that the lubricant failed? Now,another question, rather than trying to apply brakes, why not have the gears disengage when speeds or temps increase too greatly? The blades would go into a free spin until the temp cooled or the wind died down. And they would feather automatically to reduce their speed.

Why wouldn't that work?

They would probably have to make the blades more complex, and heavier, to allow them to overclock like that. :confused:

I guess fans are more complex than I thought. How did the Dutch handle this stuff for all these years?

There's are small, slow, and steerable. I believe their blades are framework skeletons, which are covered with canvas, like a sail, as needed.

At high enough rotational speeds the blades would self destruct.

Some control systems on smaller machines turn the turbine perpendicular to the wind when wind speeds get too high.

Quote:

Originally Posted by Gravdigr (Post 665009)

About a month ago I saw one of these turbines en route to who-knows-where. The things can be huge. The three turbine blades/props stopped at a local truck stop, I went back and waited around for a little while, I thought the hub might be travelling with the props, no such luck.

Great Capture!
I had no idea they were that big. they dont look that large from down on the ground. i drive past a few occasionally on the way to the airport. will drive a little faster past now.

The tail, like the ones on these 1904 St Louis World's Fair display, keep the blades pointed into the wind, like a weathervane. By folding the tail 90 degrees, it effectively shuts down the fan, either manually or as HLJ mentioned, as an automatic safety.

http://cellar.org/2010/windmills.jpg