Wind Turbine Micropitting Workshop: A Recap

Abstract

Micropitting is a Hertzian fatigue phenomenon that affects many wind turbine gearboxes, and it affects the reliability of the machines. With the major growth and increasing dependency on renewable energy, mechanical reliability is an extremely important issue. The U.S. Department of Energy has made a commitment to improving wind turbine reliability and the National Renewable Energy Laboratory (NREL) has started a gearbox reliability project. Micropitting as an issue that needed attention came to light through this effort. To understand the background of work that had already been accomplished, and to consolidate some level of collective understanding of the issue by acknowledged experts, NREL hosted a wind turbine micropitting workshop, which was held at the National Wind Technology Center in Boulder, Colorado, on April 15 and 16, 2009. Attendees agreed that it would be a small meeting of experts that allowed open discussion. To that end, it was also agreed that no formal proceedings would be published. The consensus of attendees, however, was that the workshop content was so valuable that a summary of the content and conclusions should be prepared. This report was developed for that purpose. The presentations given at the workshop can be downloaded at: http://wind.nrel.gov/public/Wind_Turbine_Gearbox_Micropitting_Workshop_2009.zip Interested readers who were not at the workshop may wish to consult the detailed publications listed in the bibliography, obtain the cited articles in the public domain, or contact the authors directly. This workshop was organized by a small committee, but its tremendous value was realized because of the contributions of many. The concept of the workshop came from Bob Errichello (GEARTECH). His longstanding experience in wind turbine gearbox failure analysis and his contact with many world-class experts enabled him to suggest both the format and most of the speakers. We are deeply indebted to him not only for his contributions for this workshop but also for his continuous contributions to wind turbine gearbox reliability. Shawn Sheng (NREL) provided all the organizational and logistical planning. He has the good technical insight into the technical topics needed to accomplish this task. He did an excellent job and clearly was the main reason for the success of the workshop. Peter Blau (Oak Ridge National Laboratory [ORNL]) collaborated on determining the technical content, writing this report, and guiding the organization of the workshop. His contributions were a key to making the meeting a success. He brought a perspective of material science to the discussion and meeting organization. Sandy Butterfield (NREL) gave the wind turbine context and related it to broad gearbox reliability issues. The speakers were by far the main attraction. Each one was a recognized expert who brought a new and different perspective of micropitting and how it could affect wind turbine reliability. The organizers want to express their deepest thanks to them for their efforts.

Tribological advancements for reliable wind turbine performance

“…This was shown by Sheng (2010), Holzhauer (1991) and Ai & Nixon (2000). Both Holzhauer (1991) and Ai & Nixon (2000) found that surface dents from hardened debris particles can lead to micropitting, which is a significant wear mode found in turbine gearbox bearings and gears today.…”

Tribochemical study of micropitting in tribocorrosive lubricated contacts: The influence of water and relative humidity

“…The delayed running-in, rough nature of the ZDDP tribofilm and its chemical modification in severe rolling-sliding contacts [36], which can enhance localised plastic deformation, are ascribed to be the reason behind micropitting-enhancing behaviour of ZDDP [37]. Alongside the ZDDP effect on micropitting, water contamination is also assumed to enhance micropitting wear in the bearings and gears lubricated with fully-formulated oils [38][39][40]. The water effect on micropitting is attributed to its destructive effect on friction-reducing and anti-wear film formation together with accelerated component surface corrosion [38,39], although the tribochemical changes in the reaction films were not studied in detail.…”

“…bearings in wind turbine gearboxes. The gear teeth and bearings in wind turbine gearboxes prevalently suffer from micropitting which especially affects the bearing's functionality [40]. Water contamination is common in wind turbine gearboxes [40] especially in off-and near-shore turbines [11].…”

“…The gear teeth and bearings in wind turbine gearboxes prevalently suffer from micropitting which especially affects the bearing's functionality [40]. Water contamination is common in wind turbine gearboxes [40] especially in off-and near-shore turbines [11]. Therefore, it is significantly important to understand the influence of water on micropitting in bearings operating in demanding applications i.e.…”

The effect of external dynamic loads on the lifetime of rolling element bearings: accurate measurement of the bearing behaviour

“…Recent research indicates that the failure rate of wind turbines is about 3 times higher than the failure rate of conventional generators [1]. This is partly due to the unique operational conditions of the bearings, resulting from widely varying wind loads and high vibration levels [2].…”