Tribology Propels Wind Energy


CLEVELAND – Friction and wear may be the biggest obstacles to harnessing wind energy, Larry Viterna, a tribologist at the NASA Glenn Research Center in Cleveland, said in his keynote address at the annual Society of Tribologists and Lubrication Engineers meeting last week. This $28 billion global market may be one of the most exciting opportunities for the lubricants industry today.

Lubricants are the life blood of todays modern wind turbines – permeating critical subsystems including the gearbox, power control actuators and numerous mechanical components, he said.

To illustrate their importance, Viterna pointed to a video of General Electric and NASA-designed Mod-2, 300 ft. diameter, 2.5-megawatt wind turbine that was operating normally in Goodnoe Hills, Washington, in 1982, until the spinning blade violently broke off. It was later determined that the pitch control mechanism had been negligently filled with dirty lubricant, triggering the collapse.

One blade pitch locked up, and then another, which resulted in loss of power and speed control, he explained. The rotor oversped by 50 percent which caused interference in the generator. The subsequent shaking shattered the windmill apart. It was a one-time design failure that was corrected to insure we monitor the condition of both of the redundant pitch control systems.

Lubricants are used in wind turbine gearboxes, hydraulic systems such as the blade pitch control, drive train brake subsystem, and bearings such as the main low speed shaft for the turbine, and the yaw bearing that provides wind direction alignment.

Viterna has studied wind energy for over 30 years and developed the formula (that bears his name) explaining the relationship between wind speed and power. Gearboxes remain our number one challenge in the industry, he said. As wind turbines goes up in diameter, you pick up more power, causing the blades to turn at lower rpm and resulting in more torque.

Originally developed in Persia in 200 A.D., and further refined through the ages, the first windmill with tail vanes that kept the blades pointing into the wind was introduced in the United States in 1854. It went on to sell six million units in the U.S. alone, mostly to pump water for livestock and steam railroads.

In 1887, Charles Brushs wind turbine in Cleveland was the first windmill to generate electricity. The technology spread across farms and the Great Plains, until the farms themselves required more power and turned to rural electrification projects for their needs in the 1930s.

The oil shocks of the 1970s renewed U.S. interest in energy alternatives such as wind power. NASA, along with General Electric, built its Mod-O, 100-watt wind turbine in 1975. It, however, suffered from numerous problems such as high sound levels radiating into nearby homes, rattling windows, interference with television reception, and low social acceptance.

The Reagan Administration cut funding for wind power research in 1987, Viterna pointed out, but since then the global appetite for energy has grown to $4 trillion annually. About a quarter of this is spent in the U.S. China will spend as much as Europe in two years, and as much as the U.S. in 10 years. Hydroelectric remains much larger as a renewable energy, but it is not growing as fast as wind due to limitations of available locations.

Today, General Electric is the largest wind energy manufacturer in the U.S. Other alternate energy sources include biofuels, geothermal, nuclear, and solar power.

Alternate energy sources like wind are addressing two of todays global challenges, the depletion of petroleum reserves and the climate change resulting from the burning of fossils fuels, he said.

He pointed out that in the early 1970s, imported oil accounted for only 28 percent of U.S. consumption. Today it is at 65 percent. By contrast, the Danish had 65 percent imported energy then, and now about 25 percent is wind energy there.

The money the United States spends on imported oil makes a difference in our balance of payments and national security. With a consistent political, economic, social and technical effort (the rest of the PEST, as Viterna called it), wind energys time could be ascendant again. In 2006, the U.S. market saw 45 percent growth in installing wind energy capacity, Viterna pointed out hopefully. And 95 percent of all new renewable energy was wind.

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