The two main types of generator are ‘turbo’ or cylindrical-rotor and salient-pole generators. Both these types are synchronous machines in which the rotor turns in exact synchronism with the rotating magnetic field in the stator.
The largest generators used in major power stations are usually turbo-generators. They operate at high speeds and are usually directly coupled to a steam or gas turbine. The general construction of a turbo-generator is shown . The rotor is made from solid steel for strength, and embedded in slots within the rotor are the field or excitation windings. The outer stator also contains windings which are located in slots, this is again for mechanical strength and so that the teeth between the slots form a good magnetic path. Most of the constructional features are very specialized, such
as hydrogen cooling instead of air, and direct water cooling inside the stator windings
so only passing reference is made to this class of machine in the following descriptions.
More commonly used in smaller and medium power ranges is the salient-pole generator.