In a synchronous motor, what can be larger than in an induction motor due to a different operation principle?

In a synchronous motor, the air gap can indeed be larger than in an induction motor, primarily due to the differences in operational principles between the two types of motors.

Synchronous motors operate based on the principle of magnetic locking between the rotor and stator fields. This means that the rotor must rotate at the same speed as the stator’s magnetic field, which is determined by the frequency of the electrical supply. The design of synchronous motors allows for a larger air gap because the rotor is magnetized, often relying on permanent magnets or field windings, rather than relying on induced currents as in induction motors. This allows for the accommodation of a greater physical distance between the rotor and stator without losing significant performance, as the rotor does not need to create its own rotating magnetic field.

In contrast, induction motors rely on the interaction between the stator's magnetic field and the rotor's induced currents, which necessitates a smaller air gap to maintain effective magnetic coupling and efficiency. Thus, in the design of a synchronous motor, a larger air gap can be utilized without adversely affecting the motor's performance, making this a distinguishing feature between the two types of motors.