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How do Wind Turbines Work?
What is wind?
Wind is moving air although you can’t see the wind itself you can see how its force affects things in its path leaves, Grass, flags, laundry on a clothesline, even your hair on a windy day.
How wind is created?
Wind is simply air in motion it is caused by the uneven heating of the earth’s surface by the sun because the Earth’s surface is made a very different types of land and water heat absorbs the sun’s heat at different rates. One example of this uneven heating can be found in the daily wind cycle.
History of wind turbine
Since ancient times people have harnessed the wind’s energy over five thousand years ago the ancient Egyptians used the wind to sail ships on the Nile River.
Later people build windmills to grind wheat and other grains the early windmills looked like paddle wheels centuries later the people in Holland improved the windmill they gave it propeller type of blades still made with sails. Holland is famous for its windmills in this country the colonists used windmills to grind wheat and corn to pump water and to cut wood. Today people occasionally use windmills to grind grain and pump water but they also use modern wind turbines to make electricity.
What is wind Turbine?
A wind turbine is a device that converts the winds kinetic energy into electrical energy. Wind turbines are manufactured in a wide range of vertical and horizontal axis types. The smallest turbines are used for applications such as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Slightly larger turbines can be used for making contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid arrays of large turbines known as wind farms are becoming an increasingly important source of intermittent renewable energy and are used by many countries as part of a strategy to reduce their reliance on fossil fuels. Wind was shown to have the lowest relative greenhouse gas emissions the least water consumption demands in the most favorable social impacts compared to photovoltaic, hydro, geothermal, coal and gas.
Main part of the Wind Turbine
- Blades:
Blades lifts and rotates when wind is blown over them causing the rotor to spin. - Rotor:
Blades and hub together form the rotor. - Tower:
Tower made from tubular steel concrete or steel lattice supports the structure of the turbine because of wind speed increases with height taller towers unable to or bias to capture more energy and generate more electricity.
- Pitch:
Pitch turns or pitches blades out of the wind to control the rotor speed and to keep the rotor from turning in winds that are too high or too low to produce electricity. - Low speed and high-speed shaft:
Low speed shaft turns a low speed shaft at about thirty to sixty revolutions per minute high speed shaft drives the generator gearbox connects the low speed shaft to the high speed shaft and increases the rotational speeds from about thirty to sixty rotations per minute to about 1000 to 1800 RPM. This is the rotational speed required by most generators to produce electricity. - Generator:
Generator produces sixty cycle AC electricity. It is usually an off the shelf induction generator. - Gearbox:The gearbox is typically used to increase the rotational speed of a low-speed rotor to a higher-speed electric generator in a wind turbine.
- Brake:
Brake stops the rotor mechanically electrically or hydraulically in emergencies
- Anemometer:
Anemometer measures the wind speed and transmits wind speed data to the controller. - Controller:
Controller starts up the machine at wind speeds of about eight to sixteen miles per hour and shuts off the machine at about fifty five miles per hour turbines do not operate at wind speeds above about fifty five miles per hour because they may be damaged by the high winds. - Wind vane:
Wind vane measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind. Yaw drive orients up wind turbines to keep them facing the wind when the direction changes down wind turbines don’t require you all drive because the wind manually blows the rotor away from it.
- Yaw system:
The Yaw drive is an important component of the Yaw system of the horizontal axis of wind turbines. In order to ensure that the wind turbine always produces the maximum amount of electricity, the Yawn drive is used to keep the rotor facing the wind as the wind direction changes.
Working principle of the Wind Turbine
Let’s see the basic working principle. When the wind is blowing the blades are turns the rotor, rotor is connected to the generator, while rotates, the rotor generator produces the electricity. Let’s get deep into the functioning of each parts and how the wind energy turns into electrical energy. First, we will see the wind blades.
The blades having the wing profile like the airplanes. The shape of the blade what makes the wind turbines to rotate but only if the angle of attack is right by pitching the blade into the wind. The blade generates lift. The direction of the airflow is the combination of the wind and the airflow caused by the rotation of the rotor near the blade root.
The radial velocity of the blade is low but on the tip of the blade the radial velocity of a turbine is as high as eighty meters per second.
This is why the tip of the blade twisted into the direction of the airflow ensures the right angle of attack to harvest as much energy from the wind as possible.
The wind turbine blades typically turn at a very low rate of R.P.M. due to the issues of the noise in mechanical strength. At this level of rotation, we cannot produce any meaningful electricity from a generator. We have to increase the speed of the rotation of the generator. So, this set up used a planetary gearbox to achieve the maximum speed.
If wind is blowing at high speed, turbine may damage so the brake system is placed to control the over speed in windy days. Electricity produced from the generator passed through a cable towards the bottom of the tower where the step-up transformer is situated.
The wind turbine should face toward the wind for maximum power generation but wind can change its direction at any time. Anemometer and wind vane is located on top of the nacelle. It measures the wind speed and direction if any changes in the wind direction, it sends to the controller.
The control system controls the yaw mechanism to rotate the nacelle with the help of yaw motor. So the wind turbine can always aligned with the winds direction.
Velocity also changing in the blade due to the wind speed. So, blade tilting mechanism is located at rotor. This is called pitch system. It tilts the blades at corresponding direction with proper alignment to ensure the velocity.
To check the efficiency of the wind turbine, measure the wind speed at upstream and downstream over a wind turbine. The wind speed of downstream is much smaller than the upstream.
Vin > Vout
This is because the blades absorb some kinetic energy from the wind the same amount of energy is converted as mechanical power of the wind turbine.
Pmech = ½ mVin 2 – ½ mVout 2
A wind turbine absorbs one hundred percent of the available kinetic energy only if the downstream wind speed becomes zero. However, zero wind speed at downstream is physically impossible condition.
Betz’s Law
Now let’s see what is betz’s law about the wind turbine. according to Betz law no turbine can capture more than 16/27, that is 59.3 percent of the kinetic energy and wind. the more kinetic energy a wind turbine pulls out of the wind the more the wind will be slowed down as it leaves. this is called Betz’s law.
Let’s prove the theory. let’s assume that the average wind speed through the rotor area is the average of the undisturbed wind speed before the wind turbine called as V1 and the wind speed after the passage through the rotor plane called as V2 that is:
(V1+V2)/2.
The mass of the air streaming through the rotor during one second is equal to
M = pF(V1+ V2)/2
Multiplication of the density of their swept area around drove her the average wind speed through the rotor area according to Newton’s second law the power extracted from the wind by the rotor is equal to
P = (1/2) m (v12 – V22)
The mass times the drop in the wind speed squared substituting M Into this expression from the first equation we get the following expression
P = (p/4)(v12-V22)(v1+v2)F
for the power extracted from the wind now let us compare our results with the total power in the undisturbed wind streaming through exactly the same area F. With no rotor blocking the wind we call this power P0.
P0 = (p/2)V13F
The ratio between the power we extract from the wind and the power in the undisturbed wind is then
(P/P0) = (1/2)(1 – (V2/V1)2)(1+(V2/V1))
We may plot P/P0 as a function of V2/V1. we can see that the function reaches its maximum for V2/V1 equals one third and that the maximum value for the power extracted from the wind is 0,59 or 16/27 of the total power in the wind.
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Animation: Hrvoje Čočić, Nandha Kumar
Story: Hrvoje Čočić
Category: Education
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