Yaw ring system could extend wind-turbine life

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Danish machining firm CNC Onsite has developed an invention for repairing wind turbine yaw rings on site. The patented system could eliminate expensive, time-consuming disassembly of the rotor and nacelle for replacement.

The yaw ring is a crucial component in securing maximum power production from a wind turbine and is complex and costly to replace. Broken and worn teeth can leave operators of older wind turbines with no choice except scrapping them.

“This inspired us to develop a repair method as an alternative,” said Søren 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.”

A diagram of the yaw ring’s location on a wind turbine. (Courtesy: CNC Onsite)

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,” 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.

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,” Kellenberger said. “So, there are far fewer days when we cannot work. This is also good for both work schedules and costings.”

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 labor – 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.

The system developed by CNC Onsite can usually carry out yaw ring repairs within a few days. This reduces downtime, and results in significant CO2 savings.

“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,” 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.”

The yaw ring repair service offered by CNC Onsite has already been used on a range of turbines in wind parks, both offshore and onshore, since it entered the market in 2019 following months of endurance tests.

More info cnconsite.dk/en