WTT-W7-Slide.pdf - Wind Turbine Mechanical Systems Assist...

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Wind Turbine Mechanical Systems to accompany Wind Turbine Technology , by A Hemami (2012) Chapter 9 Assist. Prof. Mahmut Sami BÜKER
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Introduction One of the major components of a wind turbine is the gearbox. A gearbox in machinery serves to match the speeds of the driving member and the driven member . Normally, the prime mover , a motor or an engine, which is on the driving side, is faster than the driven members and a gearbox is used to reduce that speed to a suitable value 4 In wind turbines , however, we have the exceptional case of increasing the low speed of a rotor to match the higher speed required by a generator. While the subject of gears and gear trains is much broader than what is discussed here, this chapter serves as a quick reference to gearing technology, with emphasis on the application in wind turbines .
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Gearbox fundamentals In machinery it is often necessary to change the rotational speed of a shaft to a desirable or more useful value . Mechanically this can be done, in general, by employing both belts and chains , or by using gear systems . If the distance between the two shafts is relatively large , then a belt or chain can be used; but if the space does not allow , the only solution is using gears . This is illustrated in Figure. 5 For belts two sets of pulleys are used (sprockets for chains) and in gears two gears can be meshed together . In either case, the ratio between the diameters (or radii) of the two parties determines the ratio of conversion of the rotational speeds. While distance is a primary factor, the required strength or power requirement is often more important, and in this regard, chains and belts do not have the same performance as a gearbox. In addition to the rotational speed, the direction of rotation is also a parameter that must be taken into account. While in using a belt or chain the direction of rotation does not change , in using a pair of gears there is a change in the direction of motion . A second gear can be employed to counteract this directional change , as shown in figure(c).
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Gearbox fundamentals In industry it is customary to call the smaller and larger gears the pinion and the gear ,” respectively. Here, we refer to them as the driving gear and the driven gear, as appropriate. A driving gear is also called a drive gear. 6 The scenario in above figure is not the only way to resolve the direction change . Another solution is to use an internal gear. Also, note that the radii of the gear employed to reverse direction does not have to be equal to that of either of the two gears. These themes are shown in below Figure. In an internal gear, the teeth are inside the rim. Comparing parts (a) and (b) in below figure also shows the difference in the distance between the two shaft centerlines . The idler gears in below figures (c) and (d) are free gears and their shafts do not carry a load.
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