[Mitko Gorgiev (OP)]

No, the explanation of the working principle of synchronous generators and motors is not true. I have explained that in this thread "Is Faraday's law of induction true?" https://www.thenakedscientists.com/forum/index.php?topic=78334.0, but since I have noticed that some people didn’t understand the issue in that answer, I am posting this answer as an additional explanation.

Let’s look at this picture from a textbook called “Elektronik 1” from the following authors: Helmut Röder, Heinz Ruckriegel, Willi Schleer, Dieter Schnell, Dietmar Schmid, Werner Zieß, Heinz Häberle. The picture refers to synchronous motor, but it can also refer to synchronous generator. On the picture we see a magnet, three coils and three sine curves: black, blue and red. The black sine curve corresponds to the current of the black coil. From the picture we see that in the first position of the rotating magnet the current in the black coil is zero; in the second position, the current in that coil is maximal.

motor generator.gif (108.04 kB . 602x440 - viewed 3601 times)

Just the opposite is actually true (this means: in the first position the current in the black coil is maximal; in the second, it is zero). And with this new explanation the torque from the coils upon the rotating magnet is the same at every moment of time, as it should be for its smooth rotation.

The other concept is contradictory, because the torque is not the same at every moment. Let’s take a look at the second position of the magnet when it is in line with the black coil (the current at this moment is at maximum)(the magnet rotates counter-clockwise). Until this moment the coil has attracted the white pole; then the pole goes to the left side of the coil; the coil still has the current in the same direction, which means that it still attracts the pole and thus acts against the direction of rotation. At the same moment (i.e., when the magnet is in line with the black coil) the blue and the red coil have equal currents in the same direction and both act on the opposite pole of the magnet. Thereby both exercise an attractive force. It follows that the red coil attracts the lower pole of the magnet in the direction of rotation and the blue coil attracts it against the direction of rotation. We see that on two places, both up and down, contradictory effects take place. When the upper pole of the magnet has passed the black coil a little bit, then of the three coils only the effect of the red one on the magnet will be in the direction of rotation, making the whole assembly impossible.

When the pole of the rotating magnet is moving towards the coil, then the coil attracts it. When the pole is exactly in line with the coil, then the current comes to zero, the magnetic field, too. Then a current flow begins in the contrary direction, the magnetic field of the coil is reversed and it begins to repel the pole of the magnet. This applies to a motor. The reverse applies to a generator.

The picture from the German textbook is simply an enormous LIE. Not intentional, of course, but nevertheless, a lie. The error is not accidental because the same picture can be found in many textbooks.
The true picture should look like this:

motor_generator.gif (110.15 kB . 725x440 - viewed 3590 times)

I have cut the lower part of the picture, then moved it to the right and stricken the last part. The new last part should be now copied to the first place, too (marked with the added curved arrow).

[Bored chemist]

Anything that might be worth saying about this was already said here
https://www.thenakedscientists.com/forum/index.php?topic=78334.msg589478

[Sergio_Prats]

If the black current is maximum in the first position, wouldn't its phase be very close to the red phase? In the picture, the three phases look like they are separated 2pi/3 each one which makes sense to make the flow and the torque as smooth as possible.

[evan_au]

The current phase can vary by ±90° from the voltage, depending on whether the load is capacitive, resistive or inductive. (It can even vary more than that if you drive it "in reverse".)

So it's very hard to say what is happening to the current when the load is not described (the default/ideal situation would be for a resistive load, since that provides the most efficient power transfer).

As Sergio says, in this case the 3 poles are separated by an angle of 2pi/3 = 120° so that the power delivery is constant, and the torque is smooth. Depending on the application, some large generators have a dozen or more poles, but still equally spaced to provide steady power and steady torque.

[Bored chemist]

Let’s look at this picture from a textbook called “Elektronik 1” from the following authors: Helmut Röder, Heinz Ruckriegel, Willi Schleer, Dieter Schnell, Dietmar Schmid, Werner Zieß, Heinz Häberle.

Is the book still in print?
If so, notify the publishers.
If not, forget it; it's an error in a book.