Investigation of wind turbine gearbox bearing subsurface damage considering transient loading

摘要

In this study, a failed bearing in planetary gear stage of a sub megawatt wind turbine gearbox is destructively investigated to identify different stages and features of the premature damages induced. The focus is on the role of Manganese Sulphide (MnS) inclusion in subsurface initiated damage of White Etching Areas (WEAs) and White Etching Cracks (WECs). The main types are grouped as (1) undamaged MnS inclusions; (2) inclusions separated from the matrix by gaps; (3) internal micro cracks of the inclusions; (4) micro cracks initiated from inclusions into the steel matrix; and (5) WEA around the inclusion (Butterflies). Alongside this work, the load, maximum contact pressure and subsurface stresses are calculated for the planetary bearing of NREL (National Renewable Energy Laboratory) 750 kW wind turbine during three operational conditions: shutdown, start up and normal operation. The high subsurface stress levels due to transient loading and the stress concentration around the MnS inclusion are correlated to the yielding of the material. The depth of the maximum shear stress is correlated to the dominated depth of the subsurface micro cracks. This study highlights the role of the separation of the MnS inclusions and surface traction in the subsurface initiated damage of wind turbine gearbox bearings.