Construction of Synchronous Machines

The armature winding of a conventional synchronous machine is almost invariably on the stator and is usually a three phase winding. The field winding is usually on the rotor and excited by dc current, or permanent magnets. The dc power supply required for excitation usually is supplied through a dc generator known as exciter, which is often mounted on the same shaft as the synchronous machine. Various excitation systems using ac exciter and solid state rectifiers are used with large turbine generators.

    There are two types of rotor structures: round or cylindrical rotor and salient pole rotor as illustrated schematically in the diagram below. 

Generally, round rotor structure is used for high-speed synchronous machines, such as steam turbine generators, while salient pole structure is used for low-speed applications, such as hydroelectric generators. The pictures below show the stator and rotor of a hydroelectric generator and the rotor of a turbine generator.