A Big Challenge
for Tribologists


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Image courtesy of The Timken Company.

If the U.S. is going to meet the Department of Energy’s goal for clean, renewable wind energy to supply 20% of the nation’s electricity by 2030, there are challenges that must be met.

One in particular is making sure that wind turbine components last for close to 20 years without major downtime and costly repairs.

One of the biggest obstacles facing engineers is the vulnerability and often premature failure of the costly gearbox, central to transferring the wind captured by the blades to the electrical generator that converts it into power. Gears connect a low-speed shaft to a high-speed shaft to reach the rotational speed needed by most generators to produce electricity.

Wear and Tear

Over time (in some cases, very little time), sudden changes in wind, varying ambient conditions, contaminated lubricants, or a series of issues cause excessive wear of the teeth of the metal gears, particularly in larger, heavier turbines.

“Understanding and coping with a variety of potential modes for wear and surface damage in an endless variety of mechanical systems will challenge the next generation of tribologists,” said Peter J. Blau, leader of the Tribology Research User Center Materials Science and Technology Division of Oak Ridge National Laboratory, in a 2009 presentation to the STLE/ASME International Joint Tribology Conference.

As for the gearboxes, “Wherever there are moving parts with surfaces in contact, tribology will play a role ... sometimes a critical role,” he said.

Over time, sudden changes in wind, varying ambient conditions, and contaminated lubricants cause excessive wear of the teeth of the metal gears.

Although a key component of wind turbines for years, the gearbox has posed a big challenge to tribologists, who have yet to come up with a solution to reduce stress on the bearings. Some efforts now also are focused on alternatives that do away with the gearbox altogether but there are weight, cost and other issues with direct-drive systems, too.

According to Windpower Monthly, in 2009, conventional fast-speed geared wind turbines made up 85% of the new global wind capacity, with the remaining being nongeared, direct-drive turbines.

Wind power is so important to the U.S. that in 2007, the Department of Energy formed a Gearbox Reliability Collaborative at its National Renewable Energy Laboratory in Golden, CO, the nation's primary lab for renewable energy and energy-efficiency research and development. 

The collaborative, made up of representatives of all companies with an interest in improving the gearboxes, is seeking a better understanding of the failures in order to suggest improvements in design practices and analytical tools.

Simulation Software

Advanced materials technology and sophisticated simulation software also are providing some hope.

Allowing for validation and testing of designs to determine whether the designs are going to perform in the real world without building expensive prototypes, simulation software is a factor in the rapid growth of wind farms as a viable energy alternative, says Barry Christenson, director of product management for Ansys, Inc., Canonsburg, PA, which develops and markets engineering simulation software and technologies.

With software, designers can determine how gearboxes are going to hold up by simulating on their computers different loading conditions, the weight of the blade, the forces produced by the blade turning on the turbine, transient conditions due to the wind changing direction, vibration, or other factors, all of which saves money and time, explains Christenson.

“What anyone using simulation is looking for is to reduce product development time, improve product quality, and reduce product cost,” he says.

Despite the challenges, the industry is forging ahead and is on track to meet the 2030 goal. According to the U.S. Energy Information Administration, wind power has been the fastest-growing source of new electric power generation for several years.

In 2009, the last year for which figures are available, generation from wind power increased 33.5% over 2008, bringing the share of total power generation in the U.S. to 1.95%.

Nancy Giges is an independent writer.

Understanding and coping with a variety of potential modes for wear and surface damage in an endless variety of mechanical systems will challenge the next generation of tribologists.

Peter J. Blau, Oak Ridge National Laboratory

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October 2011

by Nancy Giges, ASME.org