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Forum Index : Windmills : Storm Damage: Windmill Down
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Tim_the_bloke Senior Member  Joined: 15/11/2009 Location: AustraliaPosts: 105 |
Previously I shared my current windmill with you all at my earlier topic. This ran well until a big storm early December 2012 which brought down the tower. Sudden ground impact during high speed spinning is contraindicated for windmills but after getting it back to my workshop I now expect I will get it going again with a old set of spare blades. Images to follow. |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
The storm damaged hundreds of trees on our farm, breaching fences in dozens of places. Cattle were scattered and mixed up with other herds. A lightning strike started a bushfire which burnt much pasture but was noticed, fought and put out by neighbours. Several nearby (couple of kilometers) buildings lost roof sheeting and or collapsed. We got off lightly, with the windmill down, some water into the house and furniture blown off the verandah - still not found it all yet. Anyway, the windmill was down: 
The blades were well and truly broken. White on the fibreglass blades shows where they have folded: 
While I was looking I noticed a small (ten inches long) snake there at my feet: 
I love seeing the wildlife on the farm. Although mostly pink it was probably a baby brown snake. I would be interested if anyone can identify it for me: 
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
I was quite lucky in the way the tower failed. First to fail was the guy cable as per wind direction which was rusty. 
This would have let the tower lean maybe 20 degrees until held by the gin pole and winch. 
Then the gin cable snapped and the gin pole was twisted off the tower, letting the tower fall to 90 degrees to land on the y shaped post I have placed as a stand to hold the lowered mill for servicing. This broke to post but bounced the top tower section with the mill off the lower tower. The windmill then landed on the ground and left the lower tower above the water tank. 
This staged series of failures means my tower did not mold itself to the shape of its landing and the the mill hit the ground from a final stage fall of approx 2 metres rather than approx 8 metres. The blades are broken and unrepairable, as is the nosecone. The tower need new guy cables but otherwise is straight enough and the mill is OK except for a few dings on the cooling fins. I now have the mill back at home in my workshop and can turn it to generate voltage across each phase, so it is OK. I have a spare set of blades off an older mill which I expect I can convert to mount securely. I have a spare nosecone too. The electric wiring is OK because I have previously set it up with an in-line plug which just unplugged rather than pulling other wiring apart. No high speed blades through our roof, no-one hurt, the watertank not damaged. So, not a total loss. This Chinese mill will have another life yet. |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
I will need to buy more steel cable for replacement guy cables. Does anyone out there have an opinion on galvanised versus stainless steel, besides price? Which is stronger? Corrosion contributed to this failure. I am thinking of 4mm wire rope, attached with swages. Should I go for stainless steel over galvanised? |
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fillm Guru  Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hey Tim , All a learning curve mate , I would be using gal, I would think S/S will be costly and no swages just 3 wire rope clamps and thimbles . What did you use last time , was it new or already a tad rusty? And from looking at your original post and the pic of the mill on the tower , I would be increasing the rope angle , with that angle that looks like about under 20deg ,you are putting a lot of load on the ropes , comes back to basic rigging rules and once you start lifting loads with slings 120deg inc ( 60 deg )it de-rates by 1/2 so effectively you could be tripping + the strain load on your wire not to mention shocks. Might be something to consider PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
The tower was installed in 2006 and came with a Chinese windmill kit from Electus/Jaycar. The three cables which dame with the kit were galvanised wire rope but were Chinese poor quality. Other cables we used are from a roll of stainless steel balutrading rope we had available. The cables are fixed to the lifting anchors at the base of the water tank. We installed on the water tank as a heavy anchor and to avoid the trip hazard of the guy cables. The diameter of the tank at approx 4m sets the angle of the guy cables. |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
Hi Tim, What height is your pole for the wind turbine? I wonder if you had a look at my set up where I used an old 4 post windmill tower and a 20ft x 3" galv pole. I didn't need any guy wires, just concrete the tower legs into the ground. The thread was something like "old mill tower new use" David M. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Tim, Did you get lucky and avoid a bent rotor shaft between the front bearing and the hub? Best way to check for sure is borrow a dial gauge. I'm confused, no wait... maybe I'm not... |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
The tower is 4.5m tall and sits on top of the concrete water tank adding another 2m height. We added an acroprop inside the water tank to transfer load to the ground. The angle of the guy ropes are approx 25 degrees from the tower so 65 degrees from the ground. Is this unusually steep? Here is a photo of the original installation of the now dead Chinese windmill on the tower still in use. 
Since this photo I have added a gin pole and secondary winching tower and extra guy ropes to control the tower during lowering and raising as it was too unstable when not vertical. |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
It does not seem bent but am uncertain of this. How do I test? |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Give me a few minutes to get my boots on and I will wander down the shed and take a photo. It will be a lot easier than explaining it. I'm confused, no wait... maybe I'm not... |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Anyone with a lathe will have a dial gauge, best bet is to take the turbine to the dial gauge and let them do it, good dial gauges while not expensive, are treasured possessions and easily damaged. If it is bent you can straighten it without pulling it to pieces. Mark the high side with a texta, put the hub and nut back on to protect the taper and thread and give it a swift whack with a length of hardwood. check run-out with dial gauge, repeat as necessary. 
I'm confused, no wait... maybe I'm not... |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
A picture is worth a thousand words, thanks. I see now how to test it. Now just to source a dial gauge with magnetic stand. I will try a friend. |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hi Tim , If the shaft was bent I would be surprised , anyway below is a couple of diag taken basicly from your Pic , and uses basic Doggman/Rigger maths to work out what size wire rope will be needed on a given load . 
For the purpose of the calculation , I have put the windmill load at a 100Kg , as the tower is basically a big lever then at 1/2 way the load would be doubled but for this as I do not know I will guess at 125kg at the guy attachment , that might be a mistake and its 150kg . Then this is no different that turning it on its side and lifting 250Kg with two wire slings 
So if a 4mm rope was used then there's a high chance it will break , 8mm is required and that will have the safety factor . Firstly though, a force in Kg needs to be known from blade Dia and w/s which can be worked out , you would leave furl factor completely out as it can not be relied on and it could be coming out of furl as the gust hits PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
Wow, what a detailed answer, thank you. So the significant conclusion is that I should buy 8mm wire rope, will do. I will also need tools to cut it neatly. I think swages are tidy but was there a reason to not use them? |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
Blade diameter is approx 2m. |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Tim, I did not say you need 8mm wire rope , I gave an example of how it can be worked out and why having your guy wires not at 30 ~ 40 deg increases the load they are trying to hold, there is a lot to lifting loads and sharp edges are not your friend , I always use thimbles and wire rope grips , at least it gives you flexibility if you need to adjust over time and stretch. To work out thrust there is an equation HERE which is basically already done for a 2m turbine in 20m/s and gives a load of 66.6kg , but in 30ms it jumps up to 150kg . I don't know where you are and what type of wind strengths you see but 30m/s is aprox 108klm. So then the equation would be 150 x 2 x 2 / 8 sq/rt = 8.66 , as I mentioned this will have a safety factor for safe lifting built in , from memory it is about 4 or 5x. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
Fillm, don't worry, I will give this much more thought before assuming everything. You have giving me much to think of. A nearby farm hosts an official BOM weatherstation a few km from our farm, so data are available. The day of the storm which brought down the windmill recorded 96km/hr wind gusts, which is 27 metres per second, and the highest for a year. I am yet to finalise how to fit the replacement blades to the turbine but of the likely options the max diameter could be 2030mm with 3 blades of 100mm width. The angles are set by our setup of mounting on top of our water tank and using the water tank as the anchor. To change this would require a shorter tower or a whole new tower in a new location, neither of which we want. I don't understand the maths, but may yet with time. I note the sweep area of the blades gets used but not the area of the actual blades. Surely wide blades would cause a greater wind load on the tower as they would be a larger sail to catch the wind. I will keep thinking on all this before rebuilding. Of course theory may direct what should be done, but materials available from the hardware shop dictates what can be used. Perhaps I will end up doubling cables, but this may just mean they get to snap in series. More thinking required. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
No it doesn't work out that way. A spinning turbine has a massively higher wind loading than a stationary turbine, which is why we do the calculation based on swept area. The blade width has no real effect on tower loading for a spinning turbine. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
You tempt me to ask how come, but I am learning not to. You also inspire me to go back to uni for the physics. |
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