What is the role of the rotor in a synchronous generator?

In a synchronous generator, the rotor serves as the component that generates the magnetic field necessary for induction. Its central shaft is coupled to a mechanical prime mover, which rotates the rotor to create a changing magnetic flux.1

The rotor’s specific roles include:

• Field Production: Coils wound into slots on the rotor surface, known as the field winding, produce a magnetic field that is typically distributed sinusoidally around the rotor's periphery.1
• Voltage Induction: As the rotor spins, this rotating magnetic field passes the stator coils. According to Faraday’s law of induction, this movement induces a voltage in the stator.12
• Frequency Control: The rotor's speed and the number of magnetic poles it possesses determine the frequency of the electrical output. The relationship between the rotor speed in revolutions per minute ($N$), the frequency ($f$), and the number of poles ($p$) is defined by the formula:3
  $$N=\frac{120f}{p}$$

By adjusting the number of pole pairs, the rotor can be designed to operate efficiently at different speeds depending on the type of turbine used.3