This is a ‘wind-friendly’ article. The calculations about failure support what we’ve researched about turbine durability-
“… nearly all gearboxes in a wind farm are likely to fail within 20 years. This may seem shocking, but it is a reality in the field. Many wind operators will attest that most gearboxes have been changed or gone through an up-tower repair of some kind, such as a new high-speed stage shaft or bearings, long before its 20-year life is up.
“Now let’s ask how many gearboxes will fail within seven years? The same calculation indicates that the probability of one or more bearings failing within seven years is 37%. This means more than one-third of gearboxes will suffer some sort of bearing failure.”
Why wind-turbine gearboxes fail to hit the 20-year mark
February 1, 2018 | Michelle Froese| windpowerengineering.com
Excerpt – Read Full Article
It is also important to consider that a wind turbine has more than one bearing. A typical drivetrain has 20 to 25 bearings, including the main bearings, gearbox, and generator bearings. So, what happens if we combine the L10 life for every bearing in a drivetrain to calculate a “system-level life?” A simple calculation for a drivetrain with 25 bearings, all with an L10 design life of 20 years, indicates that the probability of one or more bearings failing within 20 years is 93%.
Based on this calculation, nearly all gearboxes in a wind farm are likely to fail within 20 years. This may seem shocking, but it is a reality in the field. Many wind operators will attest that most gearboxes have been changed or gone through an up-tower repair of some kind, such as a new high-speed stage shaft or bearings, long before its 20-year life is up.
Now let’s ask how many gearboxes will fail within seven years? The same calculation indicates that the probability of one or more bearings failing within seven years is 37%. This means more than one-third of gearboxes will suffer some sort of bearing failure.
These results come from a simplified calculation and are only intended to show overall trends, but they show some startling findings. Unfortunately, the calculation can under-estimate gearbox failure rates because it fails to account for non-fatigue failure modes. But the good news is that, in practice, some bearings offer a design life in excess of 20 years because their size is dictated by other factors, such as stiffness or safety factors during extreme load cases.
This is why the term “design life” is misleading, and one reason why many gearboxes in the field are failing in less than 20 years. One way to mitigate these failures is to employ more reliable engineering methods throughout the entire lifetime of a turbine. For example, using design standards and simulations, along with reliable operational data and historical failure rates, it is possible to provide accurate predictions of drivetrain failures.
This article was part of our 2018 Renewable Energy Guidebook. View the full publication here.
Save The Huron Mountains 