Wind

Wind Turbine Gearbox Reliability
London As a crucial failure point, gearbox reliability continues to dog the wind market and as turbines become larger the push to increase performance becomes paramount. Alstom believes it has addressed the concern by guaranteeing that torque transmission is performed independently of rotor assistance. This improves the reliability of turbine drive train elements, in distinct the gearbox, which is greater protected and subjected to reduced loads. Jordi Puigcorbe and Alexis de-Beaumont explain.

One particular of the largest issues remaining in the wind market is the reliability of the gearbox. ‘With our current wind turbine fleet presently going out of warranty period, we estimate that we are carrying a potential danger on gearboxes of about US$ 300 million. Failures are nevertheless fairly rare these days simply because our fleet is current, but we expect this will change significantly as our wind turbines strategy their 57 years of operation. Our concern is such that we are even thinking about acquiring a business with gearbox servicing capabilities.’

This statement from a big US wind farm operator is far from becoming an isolated case in an market that will see over 8000 MW of wind farm capacity go out of the warranty period each and every year in the US alone in the next handful of years.

Lately, Sandy Butterfield, a former chief wind turbine engineer at the National Renewable Power Laboratory (NREL) in Colorado, was quoted as stating that the wind market expects today’s gearboxes to last 711 years. This markedly contrasts with the 20-year design and style lifetime of the wind turbines. And the implications for the industry are large, since changing a gearbox is typically a lengthy and very costly workout.

The gearbox’s reputation for a higher failure price is linked to the extreme engineering challenge that gearbox technologies faces in wind applications, and the difficulty in effectively assessing the loads and in particular the non-torsional loads that pass by way of the gearbox and how these affect bearings and gears. Some makers have selected to move to direct drive to minimize the number of moving components in the wind turbine a lot more exposed to wear. But this has led to wind turbine particular generator styles that are generally a lot more high-priced and frequently come with each other with a lengthy-term upkeep contract with the Original Gear Manufacturer (OEM), which does not necessarily meet the operations and maintenance (O&ampM) notion of flexibility expected by buyers.

Of course, much has been done in the final decade to design and manufacture gearboxes guaranteeing a high high quality, frequently with related with more than-engineering and improved cost. Numerous efforts are also becoming place in to performing appropriate monitoring and upkeep to detect and avert any avoidable harm. These efforts have limited gearbox breakdowns in infancy, and often allowed some upkeep activities to be initiated earlier than just before, but they have not helped resolving a important trigger of the difficulty: the rotor support concept, and how it distributes loads among the wind turbine structure and the gearbox.

Loads affecting the gearbox are often underestimated due to the fact state of the art aero-elastic models do not take into account complicated non-linear phenomena made in the course of transients in the drive train like inner gearbox component dynamics coupled with bearings and help components, and the flexibility influence of the rotor assistance on the gearbox that causes added loads.

Establishing a Track Record

Alstom’s competitive availability figures are in component due to its rotor assistance notion, because much less time is required for gearbox upkeep and repair. A study of more than 200 units of Alstom’s 750 kW wind turbines has shown a gearbox failure rate under five% cumulated more than the very first nine years of operation. This number is remarkably low, and this statistic has the advantage of supplying real life operation of the Alstom Pure Torque idea for longer periods than the megawatt class wind turbines.

Alstom also analysed the efficiency of its ECO80 platform, searching at the gearbox failure statistics of a representative sample of over 600 wind turbines of 1.67 MW in more than 50 wind farms that have been operating for up to seven years, and performing endoscopic evaluation of the wind turbines that accumulated the highest quantity of operating hours in the sample. Results proved comparably high reliability efficiency of the notion in the ECO80 platform. Based on these outcomes, Alstom is confident that the majority of its wind turbines could operate with their original gearbox for their complete design and style lifetime.

Pep Prats, vice president of Advanced Technology, Wind, at Alstom, who was also a single of the founders of Ecotecnia back in 1981, comments: ‘We have worked with this style for a extended time we truly introduced it already in our extremely initial turbine, a 30 kW unit that we installed in 1984. We produced a short attempt to use a more traditional design and style in the 150225 kW turbines we sold in the 90s, but we then decided to come back to this original design and style with our 600800 kW wind turbines in the late 90s, and have since then based all our wind turbines on this idea.’

Prats continues: ‘Another advantage of this idea is its scalability. Our new ECO one hundred platform, with rotor swept areas of over 7800 m2, have to manage 20 years of extremely considerable loads. This is getting accomplished by merely scaling up our rotor help idea, with no major redesign of the shaft, assistance systems and the drive train to cope with the loads. It is a really exclusive style, with built-in reliability.’

The business normally considers gearbox as ‘consumables’, because as mentioned previously it is anticipated to be changed at least when, if not twice throughout the lifetime of their wind turbine. The Alstom Pure Torque notion gets customers away from the notion that a gearbox is a consumable.