Cracked Bearing Race Detection in Wind Turbine Gearboxes

Wind turbines are becoming established as an economically viable alternative to fossil-fueled power generation. Wind farms consisting of hundreds of units are now adding a significant amount to world generating capacity. As the size of wind farms continues to increase, business economics dictate careful asset management to minimize downtime and maximize availability and profits. A wind turbine condition monitoring system is essential to achieving that goal.

Bearing Faults and Acceleration Enveloping
Rolling element bearings usually fail by fatigue of the raceways or elements or, in generators, by electrostatic pitting of the raceways and elements. Another failure mode can involve cracking and fracture of the raceway. When a rolling element passes over a defect, the temporary loss of support causes the element to deflect slightly. When the element encounters the far side of the defect, the contact can usually produces a sharp impact to the bearing and support structure, similar to a car driving over a pothole in the road.

Summary and Conclusions
The diagnosis of a cracked inner race was based on the following evidence:
• A clear pattern of modulated impulse/response signatures in the timebase waveform. This was consistent with an inner race bearing defect.
• IRBP bearing defect and 1X modulation frequency in the envelope spectrum. This confirmed the inner race fault, and the IRBP frequency identified the offending bearing.
• Very narrow impulse/response signatures in the timebase waveform suggested a narrow defect.
• A second, identical turbine exhibited similar symptoms on the same bearing. The bearing was removed and inspected, and four inner race cracks were found. Because of this confirmation, we are now confident that the original turbine has the same problem.

** More details in the original file attached to the post