An induction machine has a stationary stator carrying AC windings and a rotor separated from the stator by a small air gap.

Stator

Balanced three-phase currents in distributed stator windings produce the rotating magnetic field that drives the machine's electromagnetic behavior.

Squirrel-cage rotor

The most common rotor uses conducting bars embedded in the rotor and short-circuited at both ends by conducting end rings. The result resembles a cage.

No external electrical connection to the cage is required in normal operation: relative motion with the stator field induces currents directly in the closed rotor conductors.

Wound rotor

A wound-rotor machine uses insulated rotor windings, usually connected through slip rings. External resistance or power-electronic equipment can then interact with the rotor circuit.

Air gap and magnetic coupling

The air gap allows mechanical rotation while keeping the stator and rotor magnetically coupled.

Because air supports magnetic flux much less readily than the ferromagnetic core, the size of the gap strongly influences the field produced for a given stator current and therefore affects machine performance.

Bearings, shaft, frame and cooling structures complete the mechanical assembly, but the essential electromagnetic structure is the interaction between the stator rotating field and closed rotor-current paths.