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supply chain Components of a Turbine Today’s utility-scale wind turbines manufacturers produce turbines that range from a 1-MW generator with a 57-meter rotor diameter on a 65-meter tower to a 3-MW generator with a 90-meter rotor diameter on a 100-meter tower. The most common turbine installed in 2008 was the GE 1.5-MW turbine, which has a 70.5- to 77-meter rotor diameter on a tower with heights ranging from 52.6 to 100 meters. The average capacity of all wind turbines installed in 2007 was 1.67 MW. Manufacturers are designing larger turbines, up to 5 MW, mostly for offshore installations. In 2008 alone, the U.S. wind industry installed over 5,000 turbines. To install that number of turbines, the U.S. industry required 15 blades and the same number of tower sections, approximately 2.4 million bolts, 27,000 miles of rebar, and 1.2 million cubic yards of concrete (enough for more than 5,700 miles of 4-foot wide sidewalk). There are over 8,000 components in each turbine assembly. Rotor The rotor for a typical utility-scale wind turbine is made of three high-tech blades, ranging in size from about 30 to 45 meters. The blades are made of laminated materials – such as composites, balsa wood, carbon fiber, and fiberglass – that have high strength-to-weight ratios. These materials are molded into airfoils to maximize the wind’s lift. The blades also often include material to protect against lightning strikes. They are bolted onto the hub, with a pitch mechanism interposed to allow the blade to rotate on its axis to take advantage of different wind speeds. The longest blade made by LM Glasfiber, the world’s largest wind turbine blade supplier, is 61.5 meters long, made for the 5-MW REPower turbine in Germany. The hub – usually made of cast iron – is one of a wind turbine’s heaviest components, weighing 8 to 10 tons for a 2-MW turbine. The hub is covered by the nose cone. Generator System The heart of the wind turbine is its electricity generating system. Inside the nacelle of a typical wind turbine, the rotor drives a large shaft into a gearbox, which steps up the revolutions per minute to a speed suitable for the electrical generator. A wind turbine gearbox must be robust enough to handle the frequent changes in torque caused by changes in the wind speed. The gearbox requires a lubrication system to minimize wear. Wind turbines being sold in the U.S. have either variable-speed or synchronous generators, depending on the model being sold. In most cases, the gearbox and generator are mounted on a bedplate to increase durability and minimize noise. As a safety mechanism, the shaft usually has two independent braking systems. The turbine has a yaw drive system to keep the rotor facing into the wind and to unwind cables. The yaw drive system usually consists of an electric or hydraulic motor mounted on the nacelle which drives a pinion mounted on a vertical shaft through a reducing gearbox. It also has a brake in order to be able to stop a turbine from turning. To control the functioning of the wind turbine, it is fitted with a number of sensors to read the speed and direction of the wind, the amount of electrical power generation, the rotor speed, the blades’ pitch, the turbine’s vibration, the temperature of the lubricants and other variables. A computer processes the inputs to carry out the normal operation of the turbine, with a safety system which can override the controller in an emergency. To condition and control the power output, the generator is equipped with a remote control and monitoring system Tower The nacelle and generator are mounted on top of a high tower to allow the blades to take advantage of the best winds. Towers are typically made of three or four tubular steel sections coated with paints and sealants and joined by bolts. Today’s wind turbine tower is usually about 70 meters tall. Most towers come with load lifting systems with load-bearing capacity of more than 400 pounds . Construction The tower is normally fitted with a base flange, which can be attached to the foundation by screwed rods cast into concrete or bolted to an embedded tower stub. For the foundation, a variety of slab, multi-pile and mono-pile solutions have been used for tubular towers, determined by the condition of the ground where the turbine is being mounted. In addition to the erection of each turbine, there is additional construction work that must be conducted to connect each turbine to the power grid, such as access road construction, laying electrical cable, and installation of an electrical substation. Transportation Transportation of turbine components often involves road, rail, and water. Given the increasing size, weight, and length of components, innovative transportation, manufacturing and logistics solutions are necessary. With respect to trucking, only a fraction of the industry is capable of managing the heavy-load long-haul requirements of the wind turbine industry. One turbine can require up to seven hauls (one nacelle, three blades and three tower sections). A truck carrying a tower section must be able to support a load with a propensity to roll that is that is over 30 meters long and weighs over 150,000 pounds. Due to tunnel and overpass restrictions, rail transport can be even more dimensionally limited than over-the-road transportation.
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