The Cracks are showing

  
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.

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“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?

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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”.

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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.

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“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.”

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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% “

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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.

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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.”

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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?”

Comments:


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

About Neil van Dokkum

Neil van Dokkum (B. SocSc; LLB; LLM; PGC Con.Lit) Neil is a law lecturer and has been so since arriving in Ireland from South Africa in 2002. Prior to that Neil worked in a leading firm of solicitors from 1987-1992, before being admitted as an Advocate of the Supreme Court of South Africa (a barrister) in 1992. He published three books in South Africa on employment law and unfair dismissal, as well as being published in numerous national and international peer-reviewed journals. Neil currently specialises in employment law, medical negligence law, family law and child protection law. He dabbles in EU law (procurement and energy). Neil retired from practice in 2002 to take up a full-time lecturing post. He has published three books since then, “Nursing Law for Irish Students (2005); “Evidence” (2007); and “Nursing Law for Students in Ireland” (2011). He is an accredited and practising mediator and is busy writing a book, with Dr Sinead Conneely, on Mediation in Ireland. His current interest is Ireland’s energy policy and its impact on the people and the environment. He is also researching the area of disability as a politico-economic construct. Neil is very happily married to Fiona, and they have two sons, Rory and Ian.
This entry was posted in EU Renewable Energy 2020 Target, The Spokes of the Wheel; wind farms; Ireland; Windfall, Wind Turbine Syndrome; Professor Alun Evans, Wind Turbines: Esen Fatma Kabadayi Whiting and tagged . Bookmark the permalink.

9 Responses to The Cracks are showing

  1. fclauson says:

    I find this ridiculous carry on that a company like Siemens is going to be any perturbed by an engineering problem.

    This is a company which has been solving engineering problems for 170 years – (to quote)

    In 1846, Werner von Siemens hit upon an idea for improving the Wheatstone telegraph. Using just simple means – cigar boxes, tinplate, pieces of iron, and some insulated copper wire – he designed his own pointer telegraph. He entrusted the apparatus‘ construction to a mechanical engineer, Johann Georg Halske, who was won over by its simplicity and reliability. In Berlin in October 1847, the two men formed their own company, Telegraphen-Bauanstalt von Siemens & Halske, and set up a small workshop in a back building at 19 Schöneberger Strasse. A week after the company was founded, the design of the pointer telegraph was awarded a patent in Prussia.

    They have been making steam turbines, gas turbines, water turbines for years – and wind turbines for a considerable length of time.

    Yes there may be some problems – but they will be solved

    • That might be comforting to future turbine owners but it certainly presents a problem to existing owners who have based their business plan on 20-25 year longevity.

      • fclauson says:

        It will be covered by something like a 5,10 or 15 year warranty and maintenance contract which are generally subcontracted out to specialist maintenance organisation.

      • Francis,

        Your point is well made but my experience of warranties is that they are carefully written exclusionary clauses, and it is often the case that you are better protected by common law and statutory law when you don’t sign the warranty. I have not been able to locate the warranty for the Siemens wind turbines but my guess would be that the warranty only extends to cover fairly moderate wind speeds which means that you would need to turn off the turbine in strong winds because the warranty will not help you. This underlines my original point – at the time we need electricity the most, in cold, wet and windy weather, the turbines are turned off and produce nothing (except for constraint/curtailment payments for the wind farm owner, see http://www.independent.ie/business/irish/windfarm-owners-were-paid-10m-not-to-produce-energy-30200656.html).

        In regards to your argument that Siemens are not the world leaders for nothing and they will soon fix these design flaws, I can say that these are fundamental design problems not covered in the latest version of the IEC61400. These design issues relate to multi-megawatt wide hub diameter wind turbines. The reason wind turbine manufacturers developed these was to extend their market from relatively windy areas to areas of relatively low wind areas. These larger wind turbines also allowed larger capacity to be deployed in fewer sites.

        These problems have been recently identified with all of these greater-than-101-meter diameter multi-megawatt wind turbines. Herr and Heidenreich are two Americans who run the AeroTorque Corporation in Wolf Creek Trail , Sharon Center, Ohio, United States and they wrote about these problems: “We are just bringing this to your attention. The critical figure here is the Wind Over Power Ratio (WOPR), which should ideally be at 4.6. This requires that either you reduce your cut- out speed or increase your rated power meters-per-second wind speed. This reduces the risks of reverse torque which destroys wind turbines transmissions.”

        Siemens in their recent specification for their 3.2 and 3.4 megawatt 101 meter hub diameter state that their cut-in speed is 15 meters per second wind. Whilst the 3 megawatt 101 meter hub diameter stays at a cut-in speed of 12 meters per second wind. The 3.2 and 3.4 megawatt wind turbines now have a WOPR of 4.6 whilst the 3 megawatt wind turbine has a WOPR of 9. Too high according to Herr and Heidenreich .
        The output curve is the level of electricity produced for each meter per second wind between cut in and cut out of the wind turbine. The rated power is the wind speed at which it achieves total rated capacity output: e.g. 3 megawatts for a 3 megawatt machine.

        These new multi-megawatt bigger than 100 hub diameter wind turbines build up enormous speed which the current design of wind turbine has difficulty slowing down in turbulent winds or at cutout. These cutouts lead to reverse torque which wrecks their transmission. To overcome these problems you either modify the design or reduce either the cut out speed. Siemens increased the speed needed to get rated output or 3 megawatts for 3 megawatt wind turbine. But doing this cuts the wind turbine’s output. And this means that the range for optimum output is reduced.

        The Wind-Over-Power-Ratio (WOPR) is calculated by dividing the cut out speed by the rated power and cubing it. For the new Siemens it is 25/15 cubed or 4.6 as per Heidenreich and Herr. Exactly the same as reducing the cutout speed to 20 meters per second and leaving the rated power at 12 meters per second wind. Again, what this does is reduces the wind turbine’s output. All because of a serious design flaw.
        Siemens actually went out of their way to use a lightweight generator with rare earth magnets. This further lightened or reduced the counter balance to increased power produced by the large blades, which were increased to enable increased electricity to be generated in low wind areas. But paradoxically this increase in blade size meant that the wind turbine’s output had to be cut to prevent them breaking up in turbulent winds or at cutout speed.

        See for example: http://www.windpowerengineering.com/design/how-turbulent-wind-abuse-wind-turbine-drivetrains/

        Extensive studies have shown that 4.6 appears to be the right WOPR. Mount Lucas and the proposed Cloncreen Wind Farm by BNM in Ireland is a case in point. Whereas 4.6 is the right WOPR, BNM’s Mount Lucas wts are at 9. Guess what will happen to them.? See John Dooley’s guest blog at http://irishenergyblog.blogspot.com/2015/11/the-impact-of-wind-turbine-density-on.html

      • fclauson says:

        It worries me when a trained barrister goes to this level of technical detail on a wind turbine gearbox 🙂

        the figures you quote must be wrong – a cut in speed of 12 or 15m/s is much higher than any thing I have found in documentation – generally its in the 3 to 4 m/s range

        the issue around slowing down is also interesting as this is generally achieved via aerodynamic breaking – that is changing the pitch of the blades to act as a break. The physical break is normally only used to bring the blades to a dead stop with a small motor used to place one blade in line with the tower. Aerodynamic breaking is well under stood in the aviation world where putting props in to “beta” pitch is a common trick to slow an aircraft down in flight – most famously used in the battle of Ka-san where large transport aircraft where flow dam near vertically out of the sky into Ka-san airstrip with props feathered thus creating massive discs air-brakes.

        The same approach can be applied to wind turbines – blades feathered to slow them down and when stopped you will note the blades twisted so that they are straight onto the oncoming wind for minimal wind resistance.

  2. fclauson says:

    One other point – the gears in a turbine are typically of a two-stage planetary gear animation: https://www.youtube.com/watch?v=tfT7Vrv71J0

    • Ah Francis, you have me – like any lawyer I have my expert whispering into my ear!

      I know more about the Siege of Khe Sanh than I do turbines. Operation Pegasus was the name of the airlift operation getting men and supplies into Khe Sanh. A good read is “Valley of Decision: The Siege of Khe Sanh” by John Prados and Ray W. Stubbe.

  3. Richard Mann says:

    News from Ontario, Canada. Wind and Solar are not reducing C02. Ontario’s own Engineering Society is telling us this. See the report, “Ontario’s Electricity Dilemma – Achieving Low Emissions at Reasonable Electricity Rates.” Ontario Society of Professional Engineers (OSPE), April 2015.
    http://www.ospe.on.ca/resource/resmgr/DOC_advocacy/2015_Presentation_Elec_Dilem.pdf

    Page 15 of 23. “Why Will Emissions Double as We Add Wind and Solar Plants ?”

    – Wind and Solar require flexible backup generation.

    – Nuclear is too inflexible to backup renewables without expensive engineering changes to the reactors.

    – Flexible electric storage is too expensive at the moment.

    – Consequently natural gas provides the backup for wind and solar in North America.

    – When you add wind and solar you are actually forced to reduce nuclear genera,on to make room for more natural gas generation to provide flexible backup.

    – Ontario currently produces electricity at less than 40 grams of CO2 emissions/kWh.

    – Wind and solar with natural gas backup produces electricity at about 200 grams of CO 2 emissions/kWh. Therefore adding wind and solar to Ontario’s grid drives CO2 emissions higher. From 2016 to 2032 as Ontario phases out nuclear capacity to make room for wind and solar, CO2 emissions will double (2013 LTEP data).

    – In Ontario, with limited economic hydro and expensive storage, it is mathematically impossible to achieve low CO2 emissions at reasonable electricity prices without nuclear generation.

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