Which generator is used in wind turbines?

Here you can see the built-in fan wheel in motion. It is mounted on one end of the rotor, which is inside the shiny steel cylinder (the stator). The radiator-like surface is used to cool the generator. With a generator like the one on the right, the details are often difficult to see. So we're going to take it apart to create a few simplified models over the next few pages.
TheA wind turbine generator converts mechanical energy into electrical energy.
Generators for wind power plants are somewhat unusual in comparison to conventional power plant generators in the network. One reason for this is that the generator is connected to a power source (the rotor) with greatly fluctuating mechanical power (torque).
On this and the following pages we assume that you have already dealt with the basics of electricity, electromagnetism and above all alternating current. If one of the terms volt (V), phase, 3-phase alternating current, frequency or Hertz (Hz) is unknown to you, you should take a look at the Electricity Handbook, and about alternating current, 3-phase alternating current, Read up on electromagnetism and induction before moving on to the next few pages.
In large wind turbines (over 100 - 150 kW) a 3-phase alternating current with normally 690 V voltage is generated. This voltage is then transformed up to 10,000 to 30,000 volts with the help of a transformer located near the system (or inside the tower), depending on the local mains voltage.
Large manufacturers of wind turbines have systems with 50 Hz (for most electrical networks in the world) and 60 Hz (for America) in their product range.
Generators have to be cooled while they are working. Most systems do this by encapsulating them and using a large fan to cool the air. Some manufacturers also use water-cooled generators. These are characterized by greater compactness, which can also lead to improved electrical efficiency. However, such systems require a cooler inside the nacelle in order to be able to radiate the heat of the liquid cooling system.
Switching the generator on and off
If we were to connect (or disconnect) the generator of a large wind turbine by simply turning a switch on or off, we would likely damage the generator, transmission, and utility power in the area.
Choice of generator and choice of network connection
Wind power plants can be equipped with either a synchronous or an asynchronous generator; the grid connection can be direct or indirect.
Direct grid connection means that the generator is directly connected to the AC voltage of the grid (normally 3-phase AC voltage).
Indirect grid connection, on the other hand, means that the generator current flows through a series of electrical components that adapt the current to the mains current. With an asynchronous generator, this happens automatically.