A wind turbine basically works on the principle of conversion of energy from one form to another. As the name itself suggests, a wind turbine makes use of wind to generate electricity. The operation of a wind turbine is the exact opposite of an electric fan. Just as an electric fan converts electrical energy into kinetic energy to circulate air in the surroundings, a wind turbine converts the kinetic energy possessed by the air flowing in the surroundings to produce electrical energy. The wind is nothing but air in motion. The wind is usually produced due to the irregularities present on the surface of the earth, the rotation of the earth, and the uneven heat supplied by the sun to various parts of the earth. The production of wind is significantly intensified in the coastal regions, which is why the maximum number of wind energy farms and wind turbines are located near such areas. A wind turbine facilitates the user to establish a non-conventional and eco-friendly source of energy. A wind turbine is advantageous as it does not release any toxic gases or waste into the environment and is one of the most efficient and economical energy sources. The limitations of using a wind turbine for energy generation include the high installation cost, difficult maintenance of the turbines, and the need for a relatively large surface area for installation. Also, the wind velocity required to rotate a wind turbine properly without causing any wear and tear problems should be more than 12 km/hr and less than 90 km/hr. The shape of the propellers of a wind turbine can be arranged in two possible shapes, i.e., along the vertical axis or along the horizontal axis. The energy produced by a wind turbine is clean and renewable, which can be used for applications such as to power a flour mill, for pumping water, cutting wood, battery charging for boats or caravans, etc. Larger wind turbines can also be used as a power source for domestic applications. An array of wind turbines arranged in order is known as a wind farm. A wind farm is capable of generating a considerably high magnitude of electrical energy that can be stored and used later.
Construction of a Wind Turbine
A wind turbine typically consists of three or five propeller blades attached to the top of a pole. All the blades of the propeller are aligned at a specific angle and are connected to a rotor. The rotor, propeller blades, and hub are collectively known as the rotor tower. The material used for the construction of a rotor tower includes concrete, tubular steel, or steel lattice. For the production of a significantly large amount of electrical energy, the height of the wind turbines is preferred to be as high as possible because the speed of wind flowing in higher regions is comparatively more than the speed of wind in the lower regions. The rotor tower section of a wind turbine is more rigid in nature as compared to the base because the top portion of the wind turbine is more exposed to high-velocity winds and is more likely to undergo wear and tear. The inner structure of the blades contains a pitch system. The main purpose of a pitch system is to tilt the propeller blades. By turning the propeller blades out of the winds, the speed of the rotor can be controlled easily and turning in of the winds that have too high or too low flow velocity can be avoided. The internal circuitry of the turbine consists of a low-speed shaft, gearbox, and high-speed shaft. Usually, the speed of a low-speed shaft is approximately equal to 30-60 revolutions per minute. The speed with which a low-speed shaft rotates can be increased up to a certain level by connecting it to a gearbox. Also, the gearbox acts as a medium to couple the rotatory motion of a low-speed shaft to a high-speed shaft. The rotation speed of a high-speed shaft is typically equal to 1000-1800 revolutions per minute. The high-speed shaft is further connected to the generator. The internal circuitry of a wind turbine also contains a brake system that is used to stop the movement of the rotor in case of emergencies or mishappenings. The braking mechanism can be operated manually, hydraulically, pneumatically, or electrically. An anemometer is attached to the backside of the turbine and is used to measure the wind velocity. The measured data or the speed value gets transmitted to the controller. The main purpose of the controller is to turn on the wind turbine machinery as soon as the wind speed reaches 10-16 km/hr and to cut off the machine when the wind velocity reaches the value approximately equal to 55 km/hr. This helps protect the machinery from damage and enables the efficient generation of electrical energy. A wind vane is connected to the turbine that is used to determine the direction of the flow of wind. It is further connected to a yaw drive and helps in the proper alignment of the turbine according to the direction of the wind. The face of the wind turbine can be adjusted according to the direction of flow of wind with the help of a yaw motor and yaw drive. Wind turbines are huge and bulky in size, hence to avoid mishappenings and accidents wind farms are usually constructed on the outskirts of the cities.
Working of a Wind Turbine
The simple operation of a wind turbine begins with the rotation of the propeller blades of the turbine with respect to their axis when the wind blows over them. The propeller blades of a wind turbine are slightly tapered in direction of the airflow and have a winged profile. The wind that causes the blade to rotate is a combination of streams of air that tend to flow in the environment at different angles and approach the blade from different directions. This is one of the reasons why the radial velocity of the turbine is low near the root of the blades and is considerably high on the tip of the blades. The range of the radial velocity of an ordinary wind turbine stretches up to a maximum value that is typically given as 80 meters per second. The twisted shape of the propeller blades ensures the right angle of attack to gather the maximum amount of kinetic energy possessed by the wind. Usually, to produce electricity with the help of a wind turbine, the movement of the fan of a wind turbine is required to be significantly high, hence the air that moves at a speed that is approximately equal to 40-45 km/hr is usually preferred. The flow of wind varies according to the area and depends a lot on the locality, hence the place for the installation of wind turbines needs to be selected with great precision and thought. The continuous movement of the fan blades gets linked to the rotor and causes it to spin. The rotor is further connected to the generator through internal circuitry. The main purpose of a generator is to convert the mechanical or kinetic energy of the spinning rotor into electrical energy. The speed with which the rotor spins is still not enough to operate a generator, which is why a planetary gearbox is used between the low-speed shaft and high-speed shaft contained by the turbine. The low-speed shaft receives input directly from the rotor tower and links it to the high-speed shaft through the gearbox. The high-speed shaft couples the rotatory motion to the generator. The electricity produced by the generator is passed through a cable and is stored by the electrical arrangement of components such as a set-up transformer, etc. present at the base of the tower. The efficiency of a wind turbine can be calculated easily by observing and noting the upstream and downstream wind velocity over the wind turbine. Ideally, the downstream speed should be zero, but practically it should be significantly less than the upstream speed. The low value of the downstream speed of the wind suggests that most of the kinetic energy possessed by the wind has been captured by the turbine and can be converted into electrical energy. Similarly, the ideal or zero value of the downstream speed suggests that 100% of kinetic energy contained by the air has been consumed and can be converted into electrical energy; however, in science, ideality does not exist. The conversion of kinetic energy can be estimated easily with the help of the Betz law. Betz law states that no wind turbine is capable of capturing more than 59.3% of the kinetic energy possessed by the wind. It also states that the more be the amount of energy that a wind turbine extracts out of the wind flowing towards its propeller blades, the less will be the velocity of the wind that flows down the propeller blades.