WTT-W6-Slide.pdf - Propeller-type Wind Turbine...

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Propeller-type Wind Turbine Characteristics to accompany Wind Turbine Technology , by A Hemami (2012) Chapter 7 Assist. Prof. Mahmut Sami BÜKER
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Introduction In this chapter, you learn more about the characteristics and properties of propeller wind turbines. As discussed previously, the word propeller will be omitted and throughout the chapter wind turbine implies the common three blade horizontal-axis wind turbine. In the course of learning the new material, it is necessary that some technical terms be known and certain techniques that are widely used in scientific and industrial application be very well understood. For this reason, some discussion at the beginning of the chapter is devoted to these terms and techniques . In particular, understanding of the term “ power in the mechanical parts of a wind turbine is quite important. 4 You also learn about characteristic curves (or characteristic diagrams) and how the relationship between two or more variables can be represented by a curve. Understanding and interpreting the meaning of a curve and the information embedded in a curve is very important.
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Mechanical power A wind turbine consists of the rotor , which catches the energy from wind and concentrates it on the shaft , and the generator , which receives the mechanical energy from the shaft (usually through the gearbox) and converts it to electrical energy . You studied the power in the wind and learned that not all of this power is usable in a turbine. You also learned some facts about generators . You have most likely noticed that power in the wind depends on the wind speed , the size of a turbine , and other parameters . When this power is transformed to a shaft, we should be able to express this power in terms of the specifics about motion of the shaft . Similarly, when this power moves to a generator, we should be able to express the power in terms of electric parameters , such as voltage and current. 5 We are going to learn about mechanical power in something that moves on a straight line , or rotates (although in a turbine we have only rotational motion , it is worth learning about power in both rotation and translational motion).
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In the metric system of units, if speed is measured in meters per second (m/sec) and force is in Newtons (N), the value of power is determined directly in Watts. Power = Speed X Force Power in linear motion 6 This expression for power is in terms of the speed and the force, both of which are mechanical parameters related to motion. Note that the force has the same direction as the motion (velocity). Figure shows an object that is under the effect of a force . It is assumed that the force passes through the object mass center and causes the object to move along a straight path with a constant velocity . In such a case, the object receives power to maintain its motion . In other words, in order to maintain the motion at the same speed, some power must be provided to the object. This power can be defined as or we can say (for British units) Power (in watts) = 2 X (speed in miles per hour) X (force in pounds)
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