Induction Motor

An induction motor is an AC electric motor that produces torque in its rotor through electromagnetic induction from the rotating magnetic field of the stator, needing no electrical connection to the rotor at all; the rotor always turns slightly slower than the stator field, a gap called slip that gives the design its alternate name, asynchronous motor. French physicist Francois Arago described the underlying rotating magnetic field concept in 1824, and Galileo Ferraris and Nikola Tesla independently built working polyphase induction motors in 1885 and 1887; Tesla patented his design in 1888 and presented it to the American Institute of Electrical Engineers that same year. Mikhail Dolivo-Dobrovolsky invented the cage rotor version in 1889, and General Electric and Westinghouse signed cross licensing agreements over the squirrel cage design in 1896. Three phase squirrel cage induction motors became the standard industrial motor because they are self starting, reliable and inexpensive, and the more recent addition of variable frequency drives has extended their use into variable speed applications where they also save energy.