AC motor

Learning objectives

To illustrate how fixed coils can be used to generate a rotating magnetic field.
To introduce one of the most useful applications of three-phase electric networks.
To visualise why the rotation speed is proportional to the frequency of the sinusoidal signal.
To illustrate how fixed armature windings behave like electro-magnets when a current runs throught them.

An electric motor converts electrical energy into mechanical energy. The innovation lies in the production of a rotating magnetic field from fixed armature windings with a sinusoidal voltage frequency running through them. Nikola Tesla perfected the uses of this device, resulting in his 1888 invention of the first three-phase electric motor.

Such motors are now everywhere: trains, washing machines, factories...

Note that these machines are reversible, that is, that you can also convert mechanical energy into electrical energy. That's what happens in power plants. The machines used in power plants are called generators, or alternators.