Diagnosis of bearing creep in wind turbine gearboxes

Georgios Alexandros Skrimpas, Zhenyan Liu, Reynir Hilmisson, Christian Walsted Sweeney, and Joachim Holboell
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phmec_16_019.pdf843.63 KBMay 29, 2016 - 1:26am

One of the most wide spread gearbox topologies in the wind energy sector consists of a slow rotating planetary stage, an intermediate speed parallel stage and finally a high speed parallel stage driving the generator rotor. The shafts of the two latter stages are supported by ball or roller bearings where their outer races are fixed to the gearbox and their inner races rotate at the corresponding shaft speed. Bearing inner race defects are frequently encountered in gearboxes leading to either replacement of the whole unit or exchange of the shaft or bearing where feasible. The present work deals with the evaluation of the development of an inner race defect from surface pitting to race axial crack resulting in excessive rotational looseness, also referred to as bearing creep. It is shown that an inner race defect can be identified efficiently at an early stage by employing well known vibration condition indicators, e.g. crest factor, whereas development to rotational looseness is expressed as increased sideband activity between the gear mesh frequencies spaced at the shaft speed supported by the defective bearing due to abnormal meshing. The condition of the gears and the shaft during the final stage of the above described failure mode is essential in regards to the possibility of uptower repairs or their use in refurbished gearboxes. Case studies from operating multi-megawatt wind turbines are presented, illustrating the progression of the fault via continuous trending of condition indicators and detailed spectral analysis of high resolution vibration signals.

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Component-level PHM
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