Wind Turbines- Relaying the Force of the Wind

11/29/2010

Humans have long used wind's power. Turbines convert its energy into electricity. With their high-tech components, they operate like mini power plants.

Wind Turbines- Sophisticated Energy Collector

Wind occurs when there are temperature differences between various parts of the earth's surface, causing different temperature and pressure areas known as anticyclones (where atmospheric pressure is higher than neighboring regions) and depressions (where falling pressure causes rotating winds).

As pressure naturally seeks to return to equilibrium, air masses move from anticyclones to areas of depression. The larger the depression, the stronger the wind.

Humans have long used this force to propel sailing craft or activate windmills. Today it is converted into electricity using wind turbines.

A number of principles govern the current design of wind turbines.

   • The power provided by a wind turbine is proportional to the wind speed cubed.The stronger the wind, the more power is released. To make the most outof as strong and constant a wind as possible, a location at elevation is used to avoid any disruption due to obstacles, whether natural (mountains or vegetation) or artificial (buildings, etc.). This is why wind turbines are so large – sometimes over 120 meters high. Another area where the wind can travel unfettered is the open sea – this is where offshore turbines are built.

   • The power of a wind turbine is proportional to the surface swept by its blades (forming a circle). Blades can be anywhere between 15 and over 60 meters long. The rotor's blades can be as much as 120 meters in diameter- as big as a football field.

Wind turbines have three main parts:

   • The tower, which supports the other components (nacelle and rotor). It is generally made of metal and set in a concrete base anchored to the ground with long stakes. Offshore turbines are anchored to the seabed in the same way.

   • The rotor converts the wind's kinetic energy (or movement) into mechanical energy. It is made up of a nose and a helix, which comprises three blades (occasionallly two).
The blades derive from aeronautical technology and are manufactured using composite materials (reinforced fiberglass polyester and/or carbon fiber); which are light, rigid, and resilient.

   • The nacelle is located at the top of the tower behind the rotor. It contains the generator that uses the moving rotor's mechanical force to produce electricity. Electric cables inside the tower transfer energy into the ground. The installed capacity (electrical production capacity) of a nacelle can be as much as 5 megawatts.

Wind turbines have a monitoring and control system to:

   • Turn the turbine rotor so it is perpendicular to wind direction to capture as much of its power as possible

   • Change the blades' angle of attack into the wind to maximize energy recovery.

With this monitoring and control system, the turbine can be automatically and quickly shut down if needed, thus ensuring operational safety at all times.

Wind Turbines- Mini Power Plants

Wind Turbines- Sophisticated Energy Collectors

To start working, a wind turbine needs a minimum wind speed of 10-15 kph. It also has an upper limit of 90 kph, more on some recent models. This limit is imposed for both safety and profitability reasons- very fast-moving parts are subject to increased wear and tear and result in minimal extra electricity output.

An internal gearbox increases the rotor's rotation speed (12-15 rpm) to about 1500 rpm, the necessary speed to ensure the alternator operates correctly.

Electronic power converters adjust the frequency of the current produced by the turbine to that of the power grid to which it is connected (50 Hz in Europe), while allowing the turbine rotor to rotate at variable wind speeds.

A power transformer located inside the nacelle or the tower increases the voltage of the electricity produced by the alternator (600-1000 volts)  to 20,000-30,000 volts. At this level, electricity can be transferred to the turbine's grid connection point.
For wind farms with capacity of 10-15 megawatts, the connection voltage level is generally 20,000 volts in France. For higher capacity wind farms, the connection voltage level can rise to 60,000-90,000 volts; and up to 225,000 volts in some cases.

[1 Source: EWEA / IEA]