I read this online, " For a travelling magnetic field in a circle, the induced magnetic field in the armature of the generator will be sinusoidal. That's why the generated voltage is a sinusoid, exactly at the same frequency as the generator is turning." I understand that the angular motion is responsible for the sine wave, however, I am very confused about what induces which. I thought magnetic field was either created with a permenant magnet or flow of charge, and that what magnetic field induces was emf, not another magnetic field. Sorry, if these all sound stupid, it all gets confusing after some time, and I don't know where to start.
A synchronous generator has a rotating magnetic field that is produced by a permanent magnet or a wound field (electromagnet). The direction of the magnetic field is such that the stator conductors pass through the flux of each pole as the rotor turns. It is the reversal of flux from one pole to the next that induces AC voltage.
For the induced voltage to be sinusoidal, the shape of the magnetic field must be sinusoidal. Designing winding configuration and the poles of the rotor to produce sinusoidal voltage is a complex task that is described in detail in electric machinery text books.