This guest blog, which appeared on the excellent Irish Energy Blog in November, has the Irish wind industry hopping and the wind turbine manufacturer Siemens, tearing it’s hair out. The secret is out – the design flaws in these big bad turbines are so fundamental that their life span is nothing near to what it says on the tin.
Fertile grounds for a flood of AIE requests, methinks.
Ps. Thanks very much to Val Martin for his explanation for technical-thickies like me.
“Thursday, 26 November 2015
Technology problems with Wind Turbines
Guest post by John Dooley
On Tuesday 24/11/2015 in a headline in The Irish Independent written by Paul Melia headed stated ” Critics of wind energy ‘ stoke fake technology fears ‘ despite success”. This quote is attributed the departing head of The Sustainable Energy Authority of Ireland DR. Brian Motherway. The question is then who are the critics of wind energy and what are the fake technology fears?
In a paper titled “ Wear Analysis of Wind Turbine Gearbox Bearings , published on March 31st 2010 by P.J . Blau Et Al of the Materials Science and Technology Division , Oakridge National Laboratory. Stated in the forward “Wind power offers a promising renewable energy option for the United States, but its implementation depends upon a combination of technological, political, and economic factors.” . This paper suggested a classification for bearing failures and identified that White Etched Area an indicator of bearing failure and suggested that the” Evidence therefore strongly suggests that they were formed by mechanical contact and not by a surface hardening treatment of some kind”.
In a piece published on April 11th 2014 by Nic Sharpley in ,Windpower Engineering & Development”, with contributions from Doug Herr and David Heidenreich from the AeroTorque Corporation ,in a wind industry publication titled “ Understanding the root cause of axial cracking in wind turbine gearbox bearings” says “Axial cracking in bearing races has become all too common in large megawatt turbines. This damage can shorten bearing life to as little as one to two years. Recent research suggests a root cause of axial cracking, making prevention and early detection possible.
“Modern wind turbines are an important piece of our energy mix. Unfortunately, gearbox life issues have impacted their financial payback. Axial cracks in bearing raceways have become a major cause of premature gearbox failures in the latest generation of wind turbines. However, it’s rare to find axial crack failures in gearbox bearings in other industries. Why damage is so common in wind turbines has been a mystery and the subject of intense research. The root cause must be understood before finding a solution.”
They go onto blame these failures on White Etch Cracks which start with White Etched Area(WEA) damage. Mentioning as well that “ Most Manufactures follow the Germanisher Lloyd guidelines, GL requires analyzing gearbox bearings for Roller Contact Fatigue resulting in a calculated life of at least 130,000 hours with the likelihood of failure at less than 10% “
They go onto question as to why if the bearings are manufactured to the required standard why they are failing in as little as 1 to 2 years. As this rarely happens in other industries. So would most other people. For those of you who say that this only affects gear driven wind turbines in 2011 Xiang Gong and Wei Qiao of the University of Nebraska published “Bearing Fault Detection for Direct-Drive Wind Turbines via Stator Current Spectrum Analysis”. I could go in to some depth as to what they say about bearing failure in Direct Drive wind turbines. However it is similar to what is quoted above.
The most significant publication of issues in ,Windpower Engineering& Development”, of wind turbine technology failings “How Turbulent winds abuse wind turbine drivetrains”. Published on May 15th 2015, a list of technology failings identified in large multi megawatt wind turbines with hub diameters of greater than 101 meters were identified. This also had contributions from Doug Herr and David Heidenreich of AerotTorque. We can start with the following quote ‘Extreme wind events have been defined for a long time. However, their ability to cause torque reversals of a magnitude that can damage a turbine has only recently been recognized and measured. The ultimate wind-load cases during normal running were defined during the 1990s in IEC 61400-1, Second Edition1, issued in 1999. This standard defined several transient wind events which turbine designers must address.” and then they say “When the standard was written, torsional reversals were not well known.”.
There are many other interesting references here to the impact of wind wake and wind shear on wind turbines in high density wind turbine wind farms. OF interest is the Texas Tech. University doppler radar of wind speed reduction for wind turbines in the lee. There is also some interesting comments on research carried out Texas Tech. University, Sandia and the NREL and how it advances industry layout standards. But that is another which could be addressed later. However the most interesting observation in this publication is the design short coming in these multi megawatt wind turbines with hub diameters of greater than 101 meters. These wind turbines, with a rated power of 12 meters per second wind and a cutout speed of 25 meters per second wind have a Wind Over Power Ratio of 9 about double what it should be. This significantly increases the risk of torque reversals. They also say the following with regard to the stresses thus caused “Of course, turbine designers do not allow this “The reason the wind industry decided to build these large multi megawatt with greater than 101 meters hub diameter was to reduce the number of sites needed and to be able to operate in lower wind speed areas, The solution they refer to is the fact that “ One turbine manufacturer, for example, has reduced the cut-out speed from 25 to 20 m/s for their 100 and 110-m rotors. This can negatively impact the annual energy production.”
Which partly negates the rational for building these large multi megawatt wind turbines with greater than 101 meter hub diameter. Not many “ Critics of wind energy’ stoke fake technology fears ‘ despite success” listed above are there?”
Val Martin – 27 November 2015 at 09:11
The only way you cam convert 20 rpm to 1750 rpm is with a step up gearbox. Engineers avoid them, they are used in Grand father clocks and wind turbines. Steel is the only material which has a hope of coping with the stress, but steel is heavy and absorbs most of the turbines power itself. Steel can be heat treated making it hard and tough, no other metal can be so treated. Imagine having half your country’s electricity supply relying on such an set up. Imagine buying a new wind farm without knowing this. As Deter Helm said on a visit to Dublin, “there will be tears”!
Val Martin – 29 November 2015 at 07:47
1) It is always a problem to explain complex engineering matters in words. Just try explaining a hand held tin can opener! On gear trains, this is a “you tube” video I found. https://www.youtube.com/watch?v=D_i3PJIYtuY there is one following it which is also useful showing a bicycle. Or search Google “Gears and Wheels You Tube”.
2) Note the term “mechanical advantage” in the 2nd video. Only in step down (reduction speed) gear trains. A small wheel driving a big wheel enables more force to be exerted on the big wheel than is imputed on the small one, but at a lower speed. Two men can open the lock gate. Note also that gear trains absorb energy which is dissipated in bearing friction and in the inertia of the cog wheels. Lubrication reduces bearing friction, but does not eliminate it. I would like to take the liberty of naming this force absorption as “resistance”.
3) In order for a gear train to transmit rotational power, the resistance of the train must be less than the power going in to it with no load. Example; assuming there is no increase/decrease in speed, (no mechanical advantage:) Force in = 15, resistance = 14, force out = 15 – 14 = 1. So for a force of 15 inward, only 1 is taken out.
4) Another example; a cog wheel with 20 cogs is driving a cog wheel with 100 cogs. (ignore speed). The mechanical advantage is 5 to 1. Force in is 1000 watts, resistance is 245 watts, what is the force out? 1,000 (100/20 ) – 245 = 5,000 – 245 = 4,755 watts. There is still plenty of force outputted.
5)Now put the big wheel (100 cogs) driving the small one (20 cogs). (mechanical disadvantage is 5/1) 1,000 (20 X 100 ) = 200 less 245 = -45. As this arrangement uses more power than is put in, it will grind to a halt. In step down (reduction speed) gear trains, the mechanical advantage will normally always exceed the resistance.
6)Now examine step up gear trains, (increasing speed gear trains). The mechanical advantage becomes mechanical disadvantage. The force transmitted is reduced and can easily reach a point where it becomes less than the resistance. In a grandfather clock, the escapement and pendulum provide controlled resistance in a mechanically disadvantaged gear train. In a wind turbine, magnetic inductance requires revvs in the order of 1,750 RPM to generate reasonable output, where as the blade speed must be kept below 20 RPM for safety.
7)If there was no resistance, this would be possible, but there is always resistance. Resistance is caused by bearing friction, cog friction, air resistance and inertia. There is a small tendency for moving objects to slow down. (the earth slows a little each year). Inertia tends to resist the turbine starting from stationary rising to full speed. Inertia is directly related to mass (weight). In fact inertia tends to resist increases in torque as the wind speed increases. (it uses valuable power)
8)In order to reduce bearing and inertia causes or resistance, the mass (weight) of the gear train must be kept to a minimum. Unfortunately, metals like aluminium and titanium are lighter, but weaker. No metal responds to heat treatment like steel does, hardened, toughened, strengthened. A turbine needs about 87 to 1 step up gear train to deliver 1, 2 or 3 mega watts equal to 15, 30 and 45 large tractor engines. Engineers try to use lighter metals, but wear and tear happens to all gears, it is a question of how long it takes. Another solution is to build the wind farm and sell on to the unsuspecting buyer before failure occurs. That is the business plan of many wind energy companies.
That’s as best as I can explain it. Google “Horse Powered Grain Separator” you tube, https://www.youtube.com/watch?v=jHstGIgBu7u