Wind turbine gearboxes: When is 20 years not 20 years?
Learning more about your wind farm can help extend the life of your gearboxes from 20 years to 25 years, and maximise your investment returns, writes Francesco Cornacchia.
It is well-known that many wind turbine gearboxes have a design life of 20 years.
However, it is also well-known that a great number of gearboxes don’t last for 20 years and fail prematurely. Why the discrepancy?
The answer lies in the way that gear and bearing lives are defined. We can’t predict the exact date on which a component will fail, but we can estimate the probability that it will last for a given duration.
A very simple calculation shows that, if we combine the expected life for every bearing in a drivetrain to calculate a ‘system level’ life, the probability of one or more bearings failing within 20 years is up to 93%. So almost all gearboxes in a wind farm are likely to fail within 20 years. It seems shocking, but isn’t far from reality.
This result comes from a simplified calculation and is intended to show the overall trend. In the course of our business, we use very sophisticated versions of this methods to analyse and forecast failure rates. Using design standards and simulations alongside a huge amount of operational data and historical failure rates, we are able to provide very accurate predictions of drivetrain failures.
Managing this risk can help wind farm owners and investors to maximise the value of their projects and reduce downtime. How can they do this?
Managing the technology and financial risks
It is of paramount importance to choose the right technology from the early development stage: the turbine must be adequate for the site conditions (wind speed, shear, turbulence, wind farm configuration) and must have a proven track record.
Investors need to assess how sensitive is design to the manufacturing processes, as this can introduce significant uncertainty to the reliability of gearboxes manufactured or refurbished by different suppliers.
The supply chain of major components needs to be considered: components that can only be manufactured by a single supplier can have a financial impact in case of serial defects, manufacturing issues or simply carry longer lead times.
Investors should also consider the maintenance quality. Even the best design in the world will not last if best practices are not followed: we have seen turbines with significant portions of the lubrication system disconnected because they were causing too many alarms. This means that many components were running without any lubrication – certainly contributing to costly failures.
Reasons for gearbox failures that investors should be aware of
Inherent design failures
Some technologies have well-known and documented design issues. Technology review and technology analysis is available
that can provide real insight into an assets future potential and future running costs.
These should and can be addressed during the commissioning sign-off phase of the wind farm construction. In the case of retrofit at the time of new technology installation. Adequate transportation, storage and installation procedures can significantly minimise the risk of premature failures.
These are possibly the easiest to influence with existing assets. Best practice O&M procedures and regimes based on data-driven CMS, SCADA, oil analysis and others will have major effects on component attrition rates, associated O&M costs and loss of revenue due to downtime.
In-depth asset health assessment and close study of the assets’ historical data combined with a full technology review of turbines and their major components will provide invaluable data for any prospective investor on future potential and running costs.
Overall, the term “design life” can be very misleading, and overwhelming evidence shows that most gearboxes in the field are failing in less than 20 years. The solution for investors is to employ better methods for assessing the key financial risks, reliability problems and working with an established partner can help.