Wind turbines use generators to transform kinetic energy into electricity. But how does a generator do that? Let’s find out what’s happening. The physical phenomenon on which generators rely is magnetic induction. Induction in a form of voltage occurs when either a conducting coil is placed in a changing magnetic field, Or when the coil moves around in a magnetic field. Most wind turbines use the first approach. The mechanical force of the blades drives the rotor of the generator. This creates a rotating magnetic flux inside the stator of armature coils. However, there are different types of generators. To simplify, we will first consider a synchronous generator with just four magnetic poles permanent magnets cause a magnetic flux or alternatively Rotor coils can be excited with a DC power source. This is what the magnetic flux would look like for a four pole rotor. When an armature coil is wrapped around a rotor the moving magnetic flux creates an alternating electromagnetic force in the coil The electrons inside the material are disturbed by the magnetic field and are forced to move in an alternating direction. The displacement of the electrons during a rotation can be plotted in a graph. this creates a sine wave pattern hence the name, alternating current. By adding two more armature coils on a 120 degree angle a three-phase current can be generated. This is generally used for transporting electric power the speed of the alternating magnetic flux defines the frequency of the current. So adding more poles and more rpm creates a higher electric frequency. Now let’s consider that the armature coils are connected to the three-phase current of a grid This 50 Hertz three-phase alternating current actually creates a rotating magnetic field like this The magnetic field of the rotor locks on to this magnetic field In a synchronous generator the rotor follows the frequency of the grid You can compare the grid with a steady moving heavy train You can push against it, but it won’t actually move faster. You’re bound to the speed of the train And how do you board a moving train? In a four pole rotor that is connected to the grid the shaft will have to turn 1500 rpm Gearbox turbines use gearboxes to increase the frequency of the rotor shaft direct drive turbines use more poles. And first system controls that the turbine speed up before connecting the generator to the grid at just the right time. Currently most wind turbines use a variable speed generator Like the doubly fed induction generator. These use power converters to allow so-called slip for the rotor speed to vary So now, you know, this is how a generator of a wind turbine makes energy for the grid This episode was brought to you by DOB-Academy if you like to learn more about offshore energy technology Make sure to subscribe and let us know if there’s a subject you want us to explain