Wind Turbine Design and Construction - Lab Report Example

?Wind Turbine Design and Construction Introduction The wind turbine is can engineering device that is used to extract wind energy transforming it into mechanical energy (rotation) or other forms of energy such as electrical energy (Burton, Sharpe, Jenkins & Bossanyi,2001). In its very basic nature, the wind turbine consists of the rotating blades, a component that points the turbine to the wind, a system to convert the mechanical rotation of the blades into other forms of energy, the control system, as well as the start and stop mechanisms. There are two main wind turbine designs, the horizontal axis and the vertical axis designs (Spera, 2009). Specifications of the Wind Device For this project, the horizontal axis wind turbine (HAWT) is considered. The horizontal axis machine is preferred due to the fact that less cost is incurred in the foundation (as a fraction of the total cost) of the structure compared to its vertical axis counterpart (Veritas, 2001). This essentially makes HAWT cheaper in cost. The design is also preferred since it does not need to be pointed at the wind direction especially where the wind direction varies almost constantly. The wind turbine is expected to operate at room temperatures (between -200C to 400C). Operating beyond these temperatures may cause the wind turbine generator to work inefficiently or cause structural damage. Furthermore, at extremely low temperatures, the generator may need external power to internal heating. The wind turbine should be ale to work efficiently at different wind speeds and directions. Very high wind speeds (beyond the survival speed) often lead to wind turbine damages according to Veritas (2001). In order to reduce the speed of rotation, a mechanical (disc) braking system will be used. The design will take into consideration the three modes of operation of the turbine; beyond rated speed, around rated speed and below rated speed operations. In order to ensure that the wind turbine operates efficiently at different wind directions, a wind vane will be fitted at the rear of the devices. The vane which also forms the tail of the wind turbine is made of a thin steel plate welded to a slender metal strip. Steel is suitable for its strength and low cost. According to past studies, the mass of a wind turbine for the survivable wind speed is best proportional to the blade length cubed (Stiesdal, 1998). The square of the blade length is also proportional to the power of the wind that is intercepted by the turbine (Stiesdal, 1998). The Rotor Unit As a matter of fact, the most visible and most vital part of the wind turbine is the bladed rotor. The rotor is the part that transforms wind energy into mechanical energy. This energy in turn causes the rotation of the turbine’s main shaft. The turbine blade is designed in such a way as to allow the streamlined flow of wind, the material at best remaining inflexible. Considering this need, the blades will be made of steel sheets. The thickness, twist and width of the blade is a compromise between the need for strength and for the streamline flow of wind (Stiesdal, 1998). Considering that the more the number of blades the greater the aerodynamic efficiency but with reducing return, the turbine to be constructed will have three blades. The transmission system The transmission system of the wind turbines acts as the link between the rotor system and the generator. The transmission system of the wind turbine is basically presented in the following figure. Fig. Transmission system The hub is made of cast iron. The complicated shape of the hub makes casting the most appropriate method for its production according to Stiesdal (1998). The material for the hub is cast iron, the material’s desirable property being its high resistance to fatigue. For such a small turbine, normal cast iron, although the material is fragile and may fracture if exposed to extreme blasts. Fig: The Wind turbine hub The main shaft of the wind turbine is commonly made of hardened steel that is tempered. For this project, hardened steel will be used. The main shaft will be machined on a lathe machine mainly through turning after facing a steel metal rod. Spherical bearings are used as the main bearing to ensure that friction and wear are reduced and therefore high efficiency is achieved in rotation as noted by Zbigniew (2003). The generator is positioned at the top of the tower near the turbine rotor hub. To couple the main shaft to the gear box, a clamping unit is used. A hollow shaft from the gear connects to the main shaft of the wind turbine through a shrink fit created by the clamping unit. The gear box is positioned between the generator and the main shaft with an aim of increasing the slow rotation of the rotor unit to the generator unit’s high speed. The gear box has a speed increase ratio, a factor that determines by how much the speed of the generator is relative to that of the rotor or drive shaft. The coupling that is used to connect the gearbox and the generator is made of steel and rubber. The permanent junction formed by the coupling between the two units if slightly flexible to accommodate differences in alignment between the two units. Fig: Coupling A generator transforms kinetic energy to electrical energy. Generators care of two main types depending on the kind of electricity that they produce; direct current (dc) and alternating current (ac) generators. For, this project, a dc generator is used. In order to control the output of the generator, the control unit will consist of a thyristor inverter and diode rectifier connected to the synchronous generator. References Burton T., Sharpe D., Jenkins N. & Bossanyi E. (2001). Wind Energy Handbook. John Wiley & Sons. Spera D. (2009). Wind Turbine Technology: Fundamental Concepts in Wind Turbine Engineering. ASME Press. Stiesdal H. (1998). The Wind Turbine: Components and Operation. Bonus Energy. Veritas D. (2001). Guidelines for Design of Wind Turbines. Copenhagen: Det Norske Veritas. Zbigniew Lubosny (2003). Wind Turbine Operation in Electric Power Systems: Advanced Modeling (Power Systems). Berlin: Springer. Read More