cooling system
The generator needs to be cooled while it is running. On most wind turbines, the generator is placed inside the tube and a large fan is used for air cooling; some manufacturers use water cooling. Water-cooled generators are smaller and more efficient, but this approach requires a heat sink in the cabin to eliminate the heat generated by the liquid cooling system.
Start and stop the generator
If you connect or unwind a large wind turbine generator to the grid by bounces an ordinary switch, you are likely to damage the generator, gearbox and adjacent grid.
Generator grid design
Wind turbines can use synchronous or asynchronous generators and connect the generator directly or indirectly to the grid. Direct grid connection refers to the direct connection of the generator to the AC grid. Indirect grid connection means that the wind turbine's current is passed through a series of electrical equipment that is adjusted to match the grid. With an asynchronous generator, this adjustment process is done automatically.
Rotor blade
Rotor blade profile (cross section)
Wind turbine rotor blades look like the wings of a craft. In fact, rotor blade designers typically design the cross-section of the most distal portion of the blade to resemble the wing of an orthodox aircraft. However, the thick profile of the inner end of the blade is usually designed specifically for wind turbines. Selecting contours for rotor blades involves many trade-offs, such as reliable operation and delay characteristics. The contour of the blade is designed to work well even when there is dirt on the surface.
Rotor blade material
Most rotor blades on large wind turbines are made of fiberglass reinforced plastic (GRP). The use of carbon fiber or aramid as a reinforcing material is another option, but such blades are not economical for large wind turbines. Wood, epoxy wood, or epoxy wood fiber composites have not yet appeared in the rotor blade market, although they have evolved in this area. Steel and aluminum alloys have problems such as weight and metal fatigue, and they are currently only used on small wind turbines.
Wind turbine gearbox
Why use a gearbox?
The energy generated by the rotation of the rotor of the wind turbine is transmitted to the generator through the main shaft, the gearbox and the high speed shaft.
Why use a gearbox? Why can't we drive the generator directly through the spindle?
If we use a normal generator and use two, four or six electrodes directly connected to a 50 Hz AC three-phase grid, we will have to use a wind turbine with a speed of 1000 to 3000 rpm. For wind turbines with a rotor diameter of 43 m, this means that the speed at the end of the rotor is higher than twice the speed of sound. Another possibility is to build an alternator with many electrodes. But if you want to connect the generator directly to the grid, you need to use a 200-electrode generator to get 30 revolutions per minute. Another problem is that the mass of the generator rotor needs to be proportional to the torque. Therefore, a directly driven generator can be very heavy.
Lower torque, higher speed
With the gearbox, you can convert the lower speed and higher torque on the rotor of the wind turbine to higher speed and lower torque for the generator. Gearboxes on wind turbines typically have a single gear ratio between the rotor and generator speed. For a 600 kW or 750 kW machine, the gear ratio is approximately 1 to 50.
A 1.5 MW gearbox for wind turbines is shown. This gearbox is somewhat unusual because flanges are mounted on the two generators at high speed. The orange-yellow fitting mounted on the right side of the generator is a hydraulically driven emergency disc brake. In the background you can see the lower part of the nacelle for a 1.5 MW wind turbine
Wind motor yaw device
The wind motor yaw device is used to rotate the wind turbine rotor to the direction of the wind.
Yaw error
When the rotor is not perpendicular to the wind direction, the wind motor has a yaw error. The yaw error means that only a small fraction of the energy in the wind can flow in the rotor area. If this only happens, yaw control will be an excellent way to control the power input to the wind turbine rotor. However, the portion of the rotor that is close to the wind source is subjected to more force than the other parts. On the one hand, this means that the rotor tends to deflect automatically against the wind, as is the case with upwind or downwind turbines. On the other hand, this means that the blade bends back and forth along the direction of the force as each rotation of the rotor. A wind turbine with yaw error will withstand a greater fatigue load than a wind turbine that yaws perpendicular to the wind direction.
Yaw mechanism
Wind turbines on almost all horizontal axes force yaw. That is, a mechanism with a motor and a gearbox is used to keep the wind turbine deflected against the wind. This figure shows the yaw mechanism on a 750 kW wind turbine. We can see the yaw bearing around the outer edge, as well as the internal yaw motor and the yaw wheel. Almost all manufacturers of upwind equipment like to stop the yaw mechanism when it is not needed. The yaw mechanism is activated by an electronic controller.
Cable twist counter
The cable is used to carry current from the wind turbine to the underside of the tower. But when the wind turbine accidentally deflects in one direction for too long, the cable will become more and more distorted. The wind turbine is therefore equipped with a cable twist counter to remind the operator that the cable should be unfastened. Similar to all safety mechanisms on wind turbines, the system is redundant. The wind turbine is also equipped with a pull switch that is activated when the cable is twisted too much.
