Induction Motor Action

Induction motors use shorted wire loops on a rotating armature and obtain their torque from currents induced in these loops by the changing magnetic fieldproduced in the stator (stationary) coils.

At the moment illustrated, the current in the stator coil is in the direction shown and increasing. The induced voltage in the coil shown drives current and results in a clockwise torque.

Note that this simplified motor will turn once it is started in motion, but has no starting torque. Various techniques are used to produce some asymmetry in the fields to give the motor a starting torque.

Simple induction motor
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Induction in Armature Coils

Induction motor action involves induced currents in coils on the rotating armature.

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Simple AC Induction Motor

A large percentage of small AC motors are classed as induction motors. This implies that there is no current supplied to the rotating coils. These coils are closed loops which have large currents induced in them because of their low resistance.

An induction motor must achieve a rotating magnetic field to continue to exert a torque on the armature coils. In this example, the rotating field is achieved by the extra coils on the pole pieces.
More detailInduction motor principle
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Simple AC Induction Motor

Induction motor principle
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