Induction motor

An induction motor is an AC motor in which a changing magnetic field in the stator induces current in the rotor. The resulting interaction produces torque without a direct electrical connection to the rotor.

Rotating magnetic field: A magnetic field whose direction rotates in space, commonly produced by polyphase alternating currents in stator windings. Its rotation sweeps past the rotor conductors and induces current.
Alternating current: Electric current that periodically reverses direction, often varying sinusoidally with time. Alternating supply currents create the changing stator magnetic field.
Variable-frequency drive: An electronic device that varies the frequency and voltage supplied to an AC motor. Changing supply frequency controls induction-motor speed and can improve energy use.
Synchronous motor: An AC motor whose rotor rotates in step with the stator's rotating magnetic field during steady operation. Unlike an induction motor, it does not require steady-state rotor slip to produce torque.
Electromagnetic induction: The production of electromotive force by a changing magnetic flux through a conductor or circuit. The stator field induces the rotor currents that make this motor work.
Three-phase electric power: A system of three alternating voltages or currents with equal frequency and phase differences of 120 degrees. Three-phase stator currents naturally create a smoothly rotating magnetic field.
Direct-on-line starting: A method of starting an AC motor by connecting it directly to its rated supply voltage. It is a simple starting method, but can draw large current from the supply.
DC motor: An electric motor powered by direct current, with torque produced through interaction between magnetic fields and current. Its operating principle and supply differ from the induction motor's AC induction mechanism.
Slip (electric motors): The difference between a motor's synchronous speed and rotor speed, expressed relative to synchronous speed. A speed difference is required to keep inducing rotor current and producing torque.
Synchronous speed: The speed of a rotating magnetic field, determined by supply frequency and the number of magnetic poles. It sets the reference speed against which rotor slip is measured.

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