As its name implies the basic difference between salient and non-salient rotor machines is the design of their rotor.
Salient Pole Machines
These machines comprise of protruding poles that have concentrated windings over them. In such machines, the rotor poles project out from the rotor core resulting in a visible pole structure. The construction is adopted in the case of slow-speed machines. Salient pole machines are practically employed in applications where high torque is desired at low speeds. The design is not applicable in the case of fast-moving machines since it becomes quite hard to retain the salient poles against large centrifugal forces that are generated.
The figure at the end displays the 2-pole salient pole machine.
Non-salient pole Machines
Non-salient pole machines are also termed as cylindrical rotor machines. Non-salient pole machines have a smooth and cylindrical rotor without any protruding poles. In such machines the rotor has several slots, here the field winding is not concentrated. Rather the field winding is distributed in several slots. The figure below depicts the basic construction of non-salient pole machines. Non-salient pole machines find their application in case of high rotating speeds. E.g turbo generators always employ cylindrical rotors that have high rotating speed of 3000 RPM and higher.
Good to know: Turbo alternators are driven by steam turbines and are very high-speed operating alternators.
The figure below illustrates the difference between salient and non-salient machines.