Wind Today - Q1 2008 - (Page 26)

T echnical Wind Gears—A Closer Look at the Drive T rain This article is based on a presentation by Paul John Baker, Moventas, Portland, OR (503-205-7947), during CanWEA’s Conference & Trade Show, Sept. 30-Oct. 3, in Quebec City, QC. In any discussion of the care and maintenance of drive trains, it’s important to understand what the gearbox in a wind turbine does, and Gearbox Wind Gearbox Challenges in Wind T urbines • Weight Weight represents the single biggest difference between standard industrial gearing and wind turbine gearing. Weight doesn’t matter to most standard industrial gearing; in wind turbines, weight drives the cost of everything. If the gearbox is bigger, the foundation and turbine must be by motors that put out constant speed and constant torque. • Little Historical Data Standard industrial drives have been in service for many years. The industry has learned the applications, gearboxes, and bearings that work best in various applications. With wind turbines, however, designs and applications change so quickly that once gearbox designers and operators think they’ve figured the system out, everything changes. Particularly difficult is adjusting to the continual growth in size of wind turbines. • Remote Maintenance Crew Wind turbine technicians, even when staffed on-site, are still relatively remote to the gearbox since they spend most of their time at least 200 feet below the turbine. Sometimes they work a mile away from the machine. This makes it difficult for technicians to detect changes in the operation of the drive train. Technicians need to be able to spend more hands-on time with the gearboxes and the drive train. Condition monitoring systems can also help address this issue. • Need for Oil Filters, Coolers, Conditional Monitoring System Standard industrial gear drives can be four times bigger than they need to be. They normally don’t get too hot or generate wear debris; therefore, they often don’t need additional cooling or oil filtration. Most drive trains on wind turbines have a single-stage planetary gearbox on the low-speed high-torque end that is married through the use of a sun pinion shaft that transmits torque from WIND TODA Y First Quarter 2008 “ a wind farm’s productivity depends upon the successful operation of each wind turbine’s gearbox for the next 15 to 20 years ” — Paul John Baker Moventas , under what conditions it operates. In general, the gearbox takes hightorque, low-speed rotational energy and converts it to high-speed, low torque rotational energy for the generator. Wind turbine generators differ from standard industrial drives in that they have to mitigate all loads mechanically, both operational and transient, for the entire drive train. Those loads can be difficult to measure, and include personal loads from wind gusting and ebbing; loads from the output side due to the generator loading and unloading; and radial and axial loads from normal operation as well as from operational misalignments. Wind turbines should be considered a heavy duty application. The American Gear Manufacturing Association (AGMA) recommends a minimum service factor of 2.0 for heavy duty applications above and beyond the design factors. The average service factor in a wind turbine drive is about 10% above and beyond the design factors. 26 larger. This all feeds into a very high power to weight ratio, impacting the economics of building a wind turbine. • Mounting Leads to Misalignments Another major difference between wind turbine drives and standard industrial drives is how they are mounted. Standard industrial drives normally are mounted to a concrete base so nothing moves. On wind turbine drives, the foundation plates that the drive rests on have the same weight restrictions as the gearbox. The gearbox is not only designed close to the edge of acceptable standards, but it has to endure massive operational misalignments and movements uptower. • Random Force Wind is not only variable, it can be random. Conditions can go from 32 meters per second (m/s) wind to nothing or to 32 m/s wind in the opposite direction in two seconds. Standard industrial drives are driven

Table of Contents Feed for the Digital Edition of Wind Today - Q1 2008

Wind Today - Q1 2008 Contents Windpower 2008 U.S. Energy Map Canada Energy Map Global Report Options and Expectations for O&M Service Providers O&M Safety Issues for Wind Farms Guanting Wind Farm to Power 2008 Olympics Operating Economics of Wind Farms Long-Term Operating Costs Post-Warranty Energy Bill Incentives May Have Another Chance Wind Gears: A Closer Look at the Drive Train Elk River Wind Farm Should Lightning Be A Concern For Wind Farms? Interview: Steve Sawyer Zephyr Powers Jiminy Peak Mountain Resort WT News: United States & Canada Interview: Willett Kempton Centennial Wind Energy WT Transmission: Southwest Power Pool EPA's Top 25 Wind Power Projects 2008 RPS Update Mark Scher, MSE Power Systems Richard Legault, Helimax Second Wind Henkels & McCoy NRG Systems Apterra Technologies, Inc. Wind Resource Maps: Michigan and New York Calendar Glossary Product Surveys Ad Index

Wind Today - Q1 2008

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