Nikola Tesla invented the first successful alternating-current induction motor in 1887.
Tesla’s design used a rotating magnetic field produced by polyphase alternating currents. That field induced currents in the rotor, making it turn without a direct electrical connection to the rotor. The simple, robust arrangement became one of the most important machines in industry.
Tesla patented related motor designs in 1887 and 1888. George Westinghouse supported their commercial development and used them in alternating-current power systems, while Thomas Edison promoted direct current during the period later called the War of the Currents.
An induction motor’s rotor normally turns slightly slower than the rotating field; this difference is called slip. Without slip, no rotor current would be induced and torque would disappear.