1.Description of HAWT wind Turbine

 A wind turbine is constituted by a tower at the top of which is the nacelle. Given as the wind speed increases as you move away from the ground, a tower can range between 50 and 80 m from above. Typically a 1 MW wind turbine is 80 meters high, which corresponds to the height of a 32-story building. The tower has the shape of a cone trunk where, inside, are arranged the cables for the transport of electrical energy, the control elements, the equipment of connection to the distribution network as well as the access ladder to the gondola. The nacelle includes the entire system for converting wind energy into electrical energy and various actuators ordered. Ring generator, Orientation drive, Rotor hub, Rotor blade, Mast, foundation

• 1-Ring generator
• 2-Machine room 
• 3-Orientation drive 
• 4-E-module 
• 5-Rotor hub 
• 6-Rotor blade 
• 7-Mast 
• 8-Foundation

E-module: The E-module is located at the base of the wind turbine tower. The power cabinets and other components are fitted at different levels of the machine. An inverter here transforms direct current into alternating current adapted to the grid.

HAWT are Two Types 

1. Classical Wind Turbines (Danish Concept Wind Turbines ).
2. Gearless Turbines.

Read more about the classifications of wind turbines

3.Power Produced by a Wind Turbine

The energy power that a wind turbine can provide is proportional to the wind speed. It is therefore advisable to seek a constant and strong wind, in height, in order to avoid any disturbance due to the natural obstacles (relief, vegetation) or artificial (buildings…), and open spaces. This is why we build large wind turbines (sometimes more than 120 meters high) and we look for free spaces, in the open sea for example with offshore wind.   The power is proportional to the area swept by the blades. The length of the blades ranges from 15 to over 60 meters. The rotor can thus reach a diameter of almost 120 meters which would entirely cover a football field.          

4.Dismantling and lifetime of wind Turbines 

The lifetime of a wind farm is estimated at 20 years, once the operation is completed, the regulations specify, in article L 553-3 of the Environment Code, that the operator of a wind turbine is responsible its dismantling and the restoration of the site.

Made of steel and plastics, a wind turbine can be dismantled at the end of its life and is almost completely recyclable and leaves no pollutants on its site. The dismantling does not, however, plan to remove the concrete base of the wind turbine, because it has no interest in being recycled: the cost of transport would be much higher than the gain obtained.


The dismantling of a wind installation must include:

• disassembly of the wind turbine.
• dismantling of additional equipment.
• dismantling of the delivery station.
• leveling the foundations.

5.Design of Wind Turbine

Big turbines can rotate at fixed or variable speeds depending on their design. Some modern turbines rely on the theory of variable speed, which allows large turbines to operate as if they were a freewheel (flywheel).   The design of large turbines requires increasing the rotation surface, which is inversely proportional to the rotation speed. In other words, the greater the length of the blade, the larger the rotation surface and the lower the speed In order to keep the blade tip speed at maximum limits.

6.How the Wind Turbine starts and when it stops?

The electronic signals emitted by the anemometer are used by the control system of the wind turbine to start the wind turbine when the wind speed reaches approximately 5 m / s. Even, the electronic control system automatically shuts down the wind turbine if the wind speed is greater than 25 m / s in order to ensure the protection of the wind turbine.

The monitoring and control system includes a computer that constantly monitors the state of the wind turbine while controlling the orientation device. In the event of a fault (for example, an over-the multiplier or generator heats up), the system automatically shuts down the wind turbine and signals to the operator’s computer via a telephone modem.

7.Power Control

1.Stall Control

In statically controlled turbines, the blades are fixed in the rotor at a fixed angle. This leads to a reduction in the energy produced at high speed, due to the presence of separation currents between the turbine blade and the wind.    

2.Pitch Control

Pitch Control In linearly controlled turbines, the turbine blades rotate linearly about their longitudinal axes, and to ensure maximum torque at the lowest speed, the operating and performance monitoring programs operate the turbine blade so that it extracts the maximum movement energy from the wind.

Read also How to study wind energy online

8.Power of wind turbines

  The capacity of wind turbines (or their size) varies from kilowatt to a few Megawatts.The length of the blade is the deciding factor in the capacity of the wind turbine, as the length of the blade increases as the rotation surface increases. At the same time, high constellations make the level of dawn higher than the level of the Earth’s surface, where the wind speed increases, and the energy density increases.   In general, large wind turbines have shown their cost better thanks to improvements in their design and to the reduction in the value of the electrical and civil works necessary for these wind turbines, and therefore their savings have improved, in particular in the case of the creation of wind farms.  

 

9.why wind turbines are three-bladed?

The wind turbine has fixed or orientable blades and rotates at a nominal speed of 25 to 40 rpm. The greater the number of blades, the greater the starting torque and the lower the speed of rotation. The single and twin-blade turbines have the advantage of weighing less, but they produce more mechanical fluctuations.
They have lower energy efficiency and are noisier since they spin faster. They cause a more visual disturbance in the opinion of landscapers. In addition, an even number of blades should be avoided for reasons of stability.

When the upper blade reaches the most extreme point, it captures the maximum power of the wind. At this moment, the lower blade crosses the sheltered zone of the wind by the tower. This provision tends to bend the entire turbine backward. This explains why 80% of manufacturers manufacture three-bladed wind turbines.

10.The required rotational speed of the rotor

The speed of rotation of the wind turbine can vary from 25  to 40 rpm. The asynchronous generator which transforms kinetic energy into electrical energy requires a rotational speed of the rotor of 1000-2000 RPM. It is, therefore, necessary to use a multiplier to increase this speed of rotation.

The Multiplier

A multiplier adapts the speed of the wind turbine to that of the electric generator (which is generally driven at around 1500 rpm). This multiplier is equipped with a mechanical brake disc actuated in an emergency when the aerodynamic brake fails or in the event of maintenance of the wind turbine.

The Alternator

The generator (or alternator) is generally asynchronous, and its electrical power may vary between 600kW and 2.5MW.

11.The reason for wind speed being variable 

On the other hand, the wind speed being variable, the characteristics of the energy delivered are variable (voltage, frequency). It is, therefore, necessary to rectify this current before delivering it to the conventional electrical network. In addition, there is a wind speed for which the power supplied by the wind turbine is maximum. Below this speed, the power is lower, beyond, the wind turbine is gradually braked through different systems:

• Pitching of the blades (Pitch control ).
• Change of direction of the wind turbine (Yaw control).
• Release of the forces applied to the blades of the wind turbine (Stall control).

12. advantages of wind energy 

In 2014 wind energy produced 3.4 percent of the global need for electricity
In 2019, The 5,000 Denmark wind turbines generate 13 .5  terawatts (TW) of energy, equivalent to 40 percent of Denmark’s need for electrical energy.

13.Disadvantages

Negative impact on areas 

The production of electricity by wind farms must occupy large areas. To produce 9 megawatts of electricity from wind energy it takes one square kilometer, while one square kilometer of solar panels produces 40 to 50 megawatts.  

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[1] : Image taken from Enercon site..

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