What are field windings in an electrical system?

Field windings refer to the coils of wire that create a magnetic field in an electrical machine, such as a generator or motor. In the context of this question, the correct answer illustrates that field windings play a crucial role in establishing the magnetic field necessary for the operation of the device.

In a typical alternator or generator setup, the stationary magnetic field produced by the field windings is essential for inducing voltage in the armature windings as they rotate. This induction is the core principle that allows electrical energy to be generated when mechanical energy is applied. Thus, the field windings are responsible for the consistent and reliable generation of the magnetic field without which the electrical machine could not function effectively.

The other choices highlight different aspects of the electrical power production system but do not accurately define field windings. For instance, the rotating part of the alternator refers to the rotor, while the component that generates current is typically the armature windings. The protective casing is not related to the function of field windings at all. Hence, the emphasis on the stationary magnetic field helps clarify the essential role that field windings play in the overall operation of electrical systems, particularly in generating electricity.