WIND POWER


Wind is the result of solar energy activity and is formed due to the unequal heating of the Earth’s surface. The airflows move because of the different temperatures of two points on Earth, having the direction from the hot point to the cold one.


The blades of the wind turbines rotate owing to the movement of the airflows and, the larger the airflow, the faster the blades rotate, producing a greater power output. The wind speed and the surface of the blades are also important to the power output.


The wind turbines may be used individually or in groups, forming wind systems.
Figure 2.1 presents an energy system consisting of wind turbines.


Figure 2.1


The wind turbine, which is presented in a simplified form in figure 2.2, is composed mainly of:
Blades

  1. Generator
  2. Brake
  3. Gearbox
  4. Electrical controls
  5. Yaw system
  6. Hub.

The blades are made of a mixture of fibreglass and composite materials. Their role is to capture _wind power and transfer it to the turbine rotor. Turbine efficiency depends on their form.
The generator ensures the production of electrical energy. It transforms the mechanical energy of the inlet shaft into electrical energy. It can be of two types, direct current or alternating current generators. The most common in use are the alternating current generators.

The brake ensures that the wind turbine is blocked on wind direction. It may be situated either on the main shaft, before the gearbox, or on the high speed shaft, after the gearbox.

The gearbox transfers mechanical energy to the generator. The electrical controls are adjustment elements.

Figure 2.2


The Yaw Assembly is necessary for the rotor axis to be aligned with the wind direction in order to extract as much of the wind’s kinetic energy as possible. It is composed of a crown gear equipped with a motor. The latter ensures the wind turbine direction and its blocking on the wind axis via the brake.

The hub is fitted with a passive, active or mixed system, which allows the orientation of the blades in order to control the rotational speed of the wind turbine.

The active control, via hydraulic engines, ensures the modification of blade angle of incidence in order to harness at maximum the instantaneous wind and limit the power, if the wind exceeds the rated speed.

With the passive control, the blades are fixed in relation to the turbine hub. They are so conceived that they could unblock in case of strong wind. It is a system used by most wind turbines.

The mixed control, also called active aerodynamic control, combines the advantages of the two systems previously mentioned.
The wind turbine has as auxiliary element the tower. The tower is manufactured from tampered steel or concrete. It supports the wind turbine. When establishing its height, the cost must also be taken into account. There is a relationship of direct proportionality between the tower height, the wind speed and the cost. The towers are 40m to 80m high, in general. The electric cables pass through the interior of the tower.

The foundation ensures the mechanical resistance of the structure made up of a tower and the wind turbine.
The wind turbines are also equipped with an electronic control system, which controls the starting up, adjustment of the blade tilt, braking and stopping of blade rotation.

Devices for measuring the wind speed can also be used.


Figure 2.3

Figure 2.3 presents a wind system situated along the coasts of Denmark.
The sequence of events in the generation and transmission of wind power can be summarised as follows:

  1. A torque is produced as the wind interacts with the rotor;
  2. The relatively low rotational frequency of the rotor is increased via a gearbox;
  3. The gearbox output shaft turns a generator;
  4. The electricity produced by the generator passes through the turbine controller and circuit breakers and is stepped up to an intermediate voltage by the turbine transformer;
  5. The grid system transmits the electricity to the locality of its end use;
  6. The site transformer steps up the voltage to the grid value;
  7. The grid system transmits the electricity to the locality of its end use;
  8. Transformer substations reduce the voltage to domestic or industrial values;
  9. Local low voltage networks transmit the electricity to domestic or industrial users.

Figure 2.4

Figure 2.4 presents a wind system in which turbines are very close to each other and are oriented at various angles.

Nowadays, technological developments permit the production of wind turbines which would make as little noise as possible, and therefore, would cause as little disturbance as possible for the neighbourhood. There are various methods of reducing the noise, such as:

  1. The soundproofing of the nacelle;
  2. The making of some mechanical transmission systems as silent as possible;
  3. The use of a silencer to restrict the vibrations;
  4. The making of highly effective and as silent as possible blade shapes.

One part of the electrical energy produced by the wind turbines can be used for local community consumption, and another one can be transferred to the national electrical network.