Right from childhood, we associate wind turbines with turning rotors. Bearings play a vital role in ensuring that the rotor can turn continually on its own axis. The wind and the constant rotary motion place huge burdens on wind turbine bearings. The main bearing absorbs all the bending moments and transverse forces of the rotor and directs them further into the tower structure. Besides larger deformations, wear and tear often shows up in the form of false brinelling or fretting corrosion. “Unfortunately, it appears that even for us, some of the main bearings have not achieved the intended lifespan of 20–25 years”, says Torsten Reusch, O&M Renewables Specialist, speaking of the 29 Fuhrländer turbines of type FL 2500/90 in the Vetrocom wind farm in Bulgaria.
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OKExchange of main bearings at Vetrocom wind farm
Reaching new heights with the right expertise
Precisely this type of Fuhrländer turbine, where the rotor is connected directly to the gearbox via the main bearing, requires the high degree of specialist knowledge that Alpiq Wind Services has gained with the support of Enertrag Service GmbH. Besides servicing and maintenance works, the portfolio also includes inspections such as gearbox endoscopies, rotor blade inspections and repairs. “The first indication of the problems with the two main bearings came from the Condition Monitoring System – CMS for short. It uses special sensors to monitor conditional changes in the gearbox, generator and main bearing. Subsequently, regular inspections within a period of one year repeatedly found metal particles in the main bearing siphons, which made exchanges unavoidable. An exchange like this is no small project: stop the facility, dismantle the rotor, exchange the bearings, reassemble the rotor, carry out test runs, and so on... In all, it takes somewhere between 9 to 15 days to exchange a main bearing”, says Torsten Reusch; and this is only for the implementation.
A serious balancing act
Planning begins long before the main bearing is exchanged. A 600 t crawler crane must be arranged, employees must be organised and the replacement parts must be sourced. When the crane is dangling the 63-ton rotor in the air, it becomes clear that the right weather conditions are also required. Because of the risk of tilting, work like this can only be carried out in wind speeds of maximum 6-7m/s. “This year, we managed to exchange the first main bearing in 14 days”, says Torsten Reusch. Colleagues are currently tackling the second turbine; they hope to have exchanged its main bearing by 03/09/2020. “So far, we are confident that we can stay on track. Our extensive experience will help us with that. In the last seven years, we have exchanged no less than eleven bearings just like this one”, says Torsten Reusch, and he reflects on previous successfully completed installation works.
