Essay: Wind turbines

1 INTRODUCTION
1.1 Wind
Wind energy is simply the air in motion. It derives energy from the moving air. It is caused by the uneven movement of air in the atmosphere. Since the Earth’s surface is made of very different types of land and water, the air moves with different velocity.
1.2 Wind Power
Wind turbines are systems that converts the kinetic energy of the wind to electrical power. Wind flows over the rotor of a wind turbine, causing it to rotate on a shaft. The resulting shaft power can be used for mechanical work, like pumping water, or to turn a generator to produce electrical power. Wind turbines span a wide range of sizes, from small roof top turbines generating less than 100 kilowatts up to large commercial wind turbines in the megawatt power range, many of which operate in large clusters called wind farms.
1.3 Betz Law
According to Betz’s law, no turbine can capture more than 59.3 percent of the kinetic energy in wind. The factor (0.593) is known as Betz’s coefficient. Practical utility-scale wind turbines achieve at peak 75% to 80% of the Betz limit.
The theoretical maximum efficiency of a wind turbine is given by the Betz Limit, and is around 59 percent. Practically, wind turbines operate below the Betz Limit.
1.4 Introduction of AMTL Wind mill
The windmill has several models .We select the AMTL 250kw model. The windmill has basic simply configurations. It has tubular tower and also lattice. The parts are high speed generator, three stage gearbox, rotor and three blades. The generation start wind velocity at 8m/s, the wind velocity has only above 8m/s, the speed reduces the generation stopped.
The top of the tower has the gearbox is fitted. The two sides of gearbox are one side is blade and other end has generator. The direction of wind flow has turned nacelle setup by the yaw drive system. The wind velocity measurement, brake system and hydraulic unit are controlled by the electronic control unit. The yaw drive system is placed in that the vertically downward to the gearbox base plate.
1.5 Wind Mill Parts
1.5.1 Blades
The rotor blades capture the wind’s energy and convert it to rotational energy of shaft. The rotor blades are usually two or more in number and are made of Glass-fibre reinforced plastic or Epoxy resin laminated wood. It also includes structures of Aluminum Copper for lightning protection and steel for the connection to the hub. The hub in turn transfers the energy to the low speed shaft. Blade designs operate on either the principle of drag or lift. For the drag design, the wind pushes the blades out of the way.
The blades can be rotated by using either drag force or lift force. Drag powered wind turbines are characterized by slower rotational speeds and high torque capabilities.
Blades come in many shapes and sizes, and there is continuing research into which design of blade is best. It turns out that the optimal design really depends on the application, or where and how the blade will be used. Designers look at the “tip speed ratio” that determines efficiency. This is the ratio between the speed of the wind and the speed the blade tip. High efficiency 3-blade-turbines have tip speed/wind speed ratios of between 6 to 7.
1.5.2 Rotor
Fiberglass rotor blades represent the most vulnerable components of a wind turbine. Lightning, Vibrations or contact with the tower can result in major damage to the blades. Design errors and manufacturing defects can also cause problems in the rotor blades during its operation time. For example, blades can develop cracks at the edges, near the hub or at the tips. The possibility of the bolts breaking due to overload also cannot be ruled out. Studies show that about 20% of the total damage due to lightning has occurred to the windmill blades.
1.5.3 Brakes
Brakes are used to stop the rotation of rotor shaft in case of power overload or system failure. The High speed shaft is equipped with an emergency mechanical disc brake, which is used in case of failure of the aerodynamic brake, or when the turbine is being serviced.
1.5.4 Power Transmission System
The low speed shaft of the wind turbine connects the rotor hub to the gearbox. The low speed shaft rotates at relatively slow speed of about 19 to 40 revolutions per minute and transfers the rotational energy from the hub to the gear box. The shaft contains pipes for the hydraulics system to enable the aerodynamic brakes to operate. The power transmission system increases the speed and transfers the rotation energy to the high speed shaft, which rotates about 50 times faster than the low-speed shaft.
1.5.5 Generator
The generator converts the rotating motion of gear box shaft into electricity at medium voltage (hundreds of volts) by the principle of Electro magnetism. Inside this component, coils of wire are rotated in a magnetic field to produce electricity. The generator’s rating, or size, is dependent on the length of the wind turbines blades because more energy is captured by longer blades. The most commonly used generator in wind turbines are induction generators or asynchronous generators.
1.5.6 Tower
Modern wind turbine generators are installed on tubular towers large turbines uses tubular tower. The tower thickness is 12mm plate. It has made up of cast iron high grade material.
MATERIAL AND SPECIFICATION
SPECIFICATION
Tower name AMTL
Customer Tuticorin Alkali Chemical &
Fertilizers Limited
Power of turbine 250KW
Year of manufacturing 20.03.1996
Life time 17 years old
Power generation per yearly 1097737units
Tower height 30m
Blade length 13.2m
Rotor 3 FRP blades, 29.20 m diameter and 670 sq. Mtrs. Swept area
Generator Asynchronous, 250 / 60 kw, 3 phase, 400 v 50 hz, 1500/1000rpm
Gear box Helical, 3 stage
Regulation Stall
Controls Micro processor based
Transformer 33 KV
MATERIAL
Large Turbines and (Small Turbines1)
Component/ Material
(% by weight) Permanent
Magnetic Materials Prestressed
Concrete Steel Aluminum Copper Glass
Reinforced Plastic 4 Wood
Epoxy 4 Carbon
Filament
Reinforced Plastic 4
Rotor
Hub (95) – 100 (5)
Blades 5 95 (95) (95)
Nacelle 2 (17) (65) – 80 3 – 4 14 1 – (2)
Gearbox 3 98 -(100) (0) – 2 (<1) – 2
Generator (50) (20) – 65 (30) – 35
Frame, Machinery & Shell 85 – (74) 9 – (50) 4 – (12) 3 – (5)
Tower 2 98 (2)
1.6 Wind Turbine Operation
A wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. Wind turbines, like windmills, are usually mounted on a tower to capture the most energy. Wind turbines operate on a simple principle. The energy in the wind turns two or three propeller-like blades around a rotor. The rotor is connected to the main shaft, which spins a generator to create electricity.
‘Figure 1.wind turbine operation’
Wind turbines are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more above ground, they can take advantage of faster and less turbulent wind. A blade acts much like an airplane wing. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much stronger than the wind’s force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin like a propeller, and the turning shaft spins a generator to make electricity. Wind turbines can be used to produce electricity for a single home or building, or they can be connected to an electricity grid for more widespread electricity distribution. Wind speed and the height of the blades both contribute to the amount of energy generated.