THE TESLA MOTOR
One of the most significant inventions of modern times
Nikola Tesla (1856-1943) – Croatian-born American physicist and electrical engineer – patented in 1887-1888 what has become the most widely used type of electric motor, the induction motor.
The induction motor is simple to make because it has no electrical contacts to the rotor. Instead it uses a rotating magnetic field produced by two or more alternating currents in the stationary outer windings (the stator). The induction motor was a major factor in the adoption of alternating current (ac) electricity supplies.
 Tesla made this working model motor to illustrate the claims in his patents. It is a two-phase machine (that is, it uses two alternating currents to produce the rotating magnetic field that makes the rotor turn). Image Credit: Science Museum/Science & Society Picture Library (Science Museum)
 These animations show how an induction motor works. The three magnets surrounding the armature (in the center) make this a three-phase machine. [Left] Alternating 3-phase sine wave current in each of the coils produces a varying magnetic field on the axis. [Right] The magnetic field vectors of the stator coils [on the outside] produce a single rotating vector.
 Drawings of the motor included in Tesla’s patent of 1888.
Patent US381968 - Electro-magnetic motor - Google Patents