Author Topic: Storm damaged turbine - rebuild  (Read 3106 times)

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Offline rossw

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Storm damaged turbine - rebuild
« on: January 18, 2012, 05:17:02 pm »
A couple of years ago we had a particularly violent storm (for our area) go through here. Winds here rarely get past 60-80kmh, this storm packed far stronger gusts. We watched branches the size of my arm fly past horizontally - after comming off a tree 100 metres away!

Anyhow, one branch went through my cheap chinese turbine, resulting in one of the blades being deflected into the tower and coming to an instant dead stop from a howling, screaming speed. I was waiting for a small lull in the wind to shut the turbine down, hand on the kill switch. 1KW rated turbine was churning out 1.3KW estimated. Then there was a bang and output stopped instantly. Followed by another thump. I was sure the turbine had come down.

A short time later the wind had calmed a little, I scooted outside to survey the damage and found this:


One blade found near the base of the tower, shredded.


The next day we found the other two blades, close to 600m downwind. They had torn free of the hub. No damage to the blades, except at the root where the 4 bolts and clamp plate were. (The blue scuffing is where they pulled out past the clamp)


Damage to the yaw shaft was immediately evident, and the broken outer cover showed how violently the head swung around to hit the tail.



The missing fibreglass from the blades is still attached to the bolts


The tower shows the impact - and the top rung of my steps has been squished


The shaft suffered a slight bend... 0.065" total deviation (so .0325" bend)


Finally got started on fixing the thing. Once I got the yaw shaft out, the damage was more evident.


I got a lump of suitable steel (70mm dia) and started to turn down a new shaft.


Playing with ideas on how much to replace, and how...


Getting a perfect fit and a glass-like finish on the shaft where the bearings are pressed on took a little patience and some fine paper. I know it didn't need this finish, but I did it anyway.


Next was to further cut up the old shaft and try to get the slipring assembly off.


And turn the new shaft to take it


I machined down the old base plate to make a snug-fitting socket for the new shaft.


It was almost a press-fit, but I still drilled and tapped a locking grubscrew for it.


The sliprings went on next, and they were a tight fit. (Shown here only part-way on)


Cut a 1.8mm grove for a circlip


Cleaned the sliprings and checked the circlip will fit properly before re-assembling.


Hard to really see here, but the hole up the middle for cables to come out still left a LOT more steel than the original thin shaft offered.


(to be continued)

Offline rossw

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Re: Storm damaged turbine - rebuild
« Reply #1 on: January 18, 2012, 05:47:17 pm »
(continues)

Next was to fix the rotor shaft. I agonised over how to straighten it, and discarded all the alternatives. In the end, since I was getting some other stuff from China (see other stories), I also got a new hub and some blades for a similar sized machine from another manufacturer. The hub is far superior to the original, however it is designed for a thinner shaft.


As were the blades! (my friend here holding one up)


So... I set the rotor up as true as I could - obviously I couldn't turn between centres if the shaft was bent. But this worked reasonably well.


I set about machining a taper to suit the new hub - and hopefully machine out the bend in the shaft!




Getting ready to put it all back together. Next was to address the sliprings and new wiring.
I machined up a small tapered ferrule


and slit it down two sides, leaving a small bit left. This will allow it to bend and flex a little


The cable is a snug fit


And the whole lot goes back into the shaft. The idea being that the harder the cable pulls down, the more the taper squeezes in and grips the cable to keep it in place.


New bearings, case cleaned and repainted, just waiting on the shaft


Awkward thing to get to, but shaft in, circlip on.


And the other end. (The grey paint is just a zinc-rich rust inhibitor)


The alternator re-assembled and back on the mast


Tail re-attached, hub and blades on.


Back and flying


The new blades are much quieter than the originals too.

Offline bvan1941

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Re: Storm damaged turbine - rebuild
« Reply #2 on: January 18, 2012, 10:06:50 pm »
Rossw,
very nice work and documentation !!
Wish I could do Lathe work like that!

In the pix showing the bent pole, it looked like one of the guy wires had parted. was that part of the problem?
If so, have you increased the guy wire size?
Keep posting your work,
Bill

Offline rossw

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Re: Storm damaged turbine - rebuild
« Reply #3 on: January 18, 2012, 10:37:25 pm »
Rossw,
very nice work and documentation !!
Wish I could do Lathe work like that!

Thanks!

Quote
In the pix showing the bent pole, it looked like one of the guy wires had parted. was that part of the problem?
If so, have you increased the guy wire size?

Just went back through the IRC logs to find contemporaneous notes...

16:22:28-22/01/09| <RossW> turbine failure
16:23:03-22/01/09| <RossW> my tower just failed, she's come down.
16:23:28-22/01/09| <RossW> Still got 70+kmh wind here, and driving rain and lightning, not game to go out to see what damage yet.
16:43:00-22/01/09| <RossW> ok, tower is intact but not well. Turbine is devoid of blades and looks like tail has smacked the back hard enough to crack it.
16:49:00-22/01/09| <RossW> funny thing really... I was watching the ammeter as it happened.
16:49:13-22/01/09| <RossW> lightning all around, waiting for a lull in the wind so I could put the brake on
16:50:13-22/01/09| <RossW> then a thump, then current rapidly dropped, then a delay (seemed like a few seconds, probably not that long)
16:50:22-22/01/09| <RossW> then another louder thump!
16:50:36-22/01/09| <RossW> I figured the second, louder one was it hitting the deck....
16:50:47-22/01/09| <RossW> just putting some pics up now.
16:50:58-22/01/09| <RossW> I've found *ONE* blade. (or whats left of it)
16:51:30-22/01/09| <RossW> listening to the airport, they're diverting aircraft all over the place. Cops are running around like headless chickens with trees over roads, power lines down etc.
17:00:11-22/01/09| <keith> once the guy snapped   the forces went through the roof
17:00:25-22/01/09| <RossW> the guy didn't snap....
17:00:41-22/01/09| <keith> no?
17:00:43-22/01/09| <RossW> it looks like the chain the turnbuckle was attached to has failed.
17:01:03-22/01/09| <keith> ok
17:01:29-22/01/09| <RossW> I did all the right stuff with the guy. It's 8mm, not the 4mm they supplied. It has proper thimbles (none were supplied) etc.


So, the guy wire hadn't actually broken, and I've (subsequently, as a result of that) re-done the way the guys attach to the anchors. They can't come out like that again!  But the guy comming off was an effect, not a cause.