On more and more places you can found a park wind turbines. Often you see them along the highways, in the sea or in an open landscapes. Using the natural energy and thus saving fossil fuel is an important theme. A windturbine uses the power of the wind for generating electricity. A windturbine has three blades, the rotating movement sets a generator in motion and it will generate electric energy. He is effective at a wind speed of 3 meters per second. Its maximum rotation is 25 meters per second because of the safety. The beginning of the report is about the wind turbines in general, different types and construction. The last part is more zoomed in on the blades.
Types
There are two types of wind turbines. The difference is the direction of the rotation-axis. The vertical-axis turbine isn’t dependent on the wind direction. He is very suitable for a built environment. In the Netherlands most turbines have a horizontal-axis turbine.
Structure
The structure of a wind turbine is roughly divided into two parts; a tower and the gondola. The tower is about 100 meters and the gondola 40 meters. At the front of the gondola three turbine blades are placed with a diameter of 80 meters. The blades are fixed on an axis that runs in the gondola. In the gondola the gearbox, generator and transformer are placed. The gondola is connected with the tower and is able to rotate, so that the nose of the gondola is always point in the wind direction. At the bottom of the tower there is a computer that controls all wind directions and speeds. The current is led through a cable to the power station.
As mentioned the gondola includes the components in order to concert the rotation to electricity. Where the blades are fixed on the gondola, there are three big circular openings. In these openings fit the blades. The blades has a blunt at the end and the blunts are fixed on the horizontal axis. The rotating movement of the axis is accelerated in the gearbox. The gearbox drives the generator then. A generator is like a dynamo. In a dynamo, the rotary motion will be convert into electricity. In the tower, there is a transformer which increases the current voltage further.
Turbine blades
The cross section of a blade has a teardrop shape. The shape grows as it nears the top of the gondola. The turbine blades are inspired by the wings of an airplane. If the blades are hold horizontally, then there is under pressure, suction, on the top. This wing is pushed upward, lifting. When the wing is rotated to a certain angle, the lifting is stopped and there is a break. The air flow is blocked.
The three blades have an equal weight. A blade of 27 meters weights 2.4 tonnes. A blade of 49 meters weights 10 tons. Most rotor blades for large wind turbines are made of fiberglass reinforced plastics (GPR) glass fiber reinforced polyester or epoxy. Glass fiber mats, light woods and resins are the basis for a wind turbine blade. Layer by layer the fiberglass are placed on each other, and mixed with resin to a virtually indestructible composite material. Here and there comes a layer of wood between. With the exception of the screws, to fix the blade on the turbine, is the only metal part is a lightning conductor. Which is incorporated on the end of the blade. The lifetime of a blade is approximately 15-20 years.
Controllability blades
The connection between the blade and the front of the gondola is a circle in an opening in the stump. In the stump are gear wheels which ensure that the blades can be rotated. This controllability is called pitch. This system is taken from the airplane technology. A supervised machine measures the number of rotations per second. The controller performs the pitch when it is necessary. This control is very imprtant. The turbine is very light weight and has a large diameter. There are large velocities involved. the outer edge of a sheet can reach a speed of 64 m/s.
