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New yaw ring repair method makes wind turbine lifetime extension viable

  • Patented system makes yaw ring repairs economically feasible
  • Danish company CNC Onsite’s method can extend wind turbine life
  • Repair versus replacement represents a significant CO2 reduction
  • New tool is portable, compact and separable to allow in-situ repairs

Vejle, Denmark, 22 February, 2022 – A new invention for repairing yaw rings in-situ is expected to make a major contribution to extending the lifespan of wind turbines. Developed by Danish machining expert CNC Onsite, the patented system means the yaw ring does not need to be replaced, eliminating the expensive, time-consuming and potentially detrimental disassembly of the rotor and nacelle.

A crucial component in securing maximum power production from a wind turbine, the yaw ring, also called a “yaw gear rim”, is complex to replace. Yaw ring replacement costs are so high that broken or worn teeth can leave operators of older wind turbines with little choice other than scrapping them.

“This inspired us to develop a repair method as an alternative,” Søren Schmidt-Kellenberger, Sales Director, CNC Onsite.

“We can now offer a repair service for both onshore and offshore at a fraction of the cost of replacing the entire yaw ring, and that makes it viable to keep perfectly good wind turbines operating for longer,” he added.

Patented portable precision tool

The CNC Onsite method employs a portable precision tool to repair any broken or worn yaw ring teeth. Operated by a specialist engineer, the tool applies the patented method, working at extremely fine tolerances, to remove and reinsert machined teeth. The patent for the system covers the milling process by which the damaged teeth are excised, and the bed created for the new part, as well as its particular insertion method.

“The process we apply when creating new yaw ring teeth for a wind turbine is similar in principle to a new dental crown that is first copied precisely then fitted by a dentist using precision tools,” Schmidt-Kellenberger said. “The aim is the same, and it should last for a long time.”

The tool has been designed to break down into component parts with a low weight that allows them to be transported in the tower elevator to the work area. After reassembly in the nacelle, the compact tool can be operated in the confined working space around the yaw ring.

Not weather dependent

The repairs are carried out inside the wind turbine tower so can be completed irrespective of weather conditions.

“As long as it is safe to travel to and access the wind turbine, we can

carry out the repairs. So there are far fewer days when we cannot work. This is also good for both work schedules and costings,” Schmidt-Kellenberger explained.

Scale of the problem

Mounted at the top of the wind turbine tower, the toothed yaw ring is a gear that engages with motors mounted on the nacelle to align the rotor blades with the wind. CNC Onsite estimates that turbines on some 5 to 10 percent of wind farms will experience damage to their yaw ring teeth during their service life. Typical causes include unpredictable wind events or uneven loads sustained over time.

Replacing the yaw ring requires the entire nacelle to be detached using a crane and specialist labour – a process that is expensive for onshore turbines and perhaps uneconomic for offshore. Across the lifetime of a wind turbine, maintenance can represent up to a quarter of all costs incurred, and decisions such as choosing a cost-effective yaw ring repair versus replacement are set to become an important trend.

CO2 savings

The system developed by CNC Onsite can usually carry out yaw ring repairs within a few days. This not only reduces downtime, but results in significant CO2 savings too.

“We’re eliminating the need for manufacturing a new yaw ring and above all the huge logistical effort required to transport a yaw ring to the site, deploy cranes, which is particularly tricky offshore, and replace it,” Schmidt-Kellenberger said.

“Such an operation requires a significant number of people and a lot of equipment with all the  associated CO2 emissions. With our repair method,this is no longer required,“ he added.

“The fact that whenever you take down the nacelle there is a potential risk of damage to it and especially to the blades which is another factor that cannot be ignored,” Schmidt-Kellenberger added.

The yaw ring repair service offered by CNC Onsite has already been used a range of                                            turbines, both offshore and onshore, since it entered the market in 2019 following many months of endurance tests, proving that the replaced teeth are robust over time.

For further technical information and illustrations, please contact:

Søren Schmidt Kellenberger
+45 25 53 76 50