Design of Highly Loaded Slewing Bearings – The Collaborative Project HBDV

Most modern wind turbines are designed for a service life of 20 years according to IEC 61400–1. The size of turbines has increased within the last years, but the load density has as well. To increase energy yield and reduce levelized costs of electricity, new innovative concepts and advanced control strategies are being developed and utilized. For an efficient operation of wind turbines, the rotor and its blades have to be adapted dynamically to environmental conditions. Most common nowadays is the so-called Individual Pitch Control (IPC), which means an independent and dynamic adjustment of blade angles to the wind conditions considering respective positions during operations of a wind turbine. If the pitch of the wind turbine blades is adjusted by IPC, some significant load reductions can be achieved. Due to the continuous readjustment of the rotor blade, the load on the blade changes dynamically while the pitch bearing is permanently exposed to oscillating motions, which lead to insufficient lubrication conditions and result in surface damage mechanisms. Depending on load, oscillation angle, frequency and other parameters, bearings can thus fail long before the intended service life. Some common failure mechanisms are false brinelling, fretting corrosion and premature rolling contact fatigue.