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