Linear induction motor

A typical 3 phase linear induction motor. The "primary" core (grey) has grooves, and the windings are laid into them on top of each other. An aluminium plate above (not shown) serves as "secondary" and will move relative to the primary if a 3 phase AC is applied.
A transverse flux linear induction motor (here the primary is at top of picture) and has two sets of opposite poles side by side. (Picture from US Patent 3824414 by Eric Laithwaite)

A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characteristically, linear induction motors have a finite primary or secondary length, which generates end-effects, whereas a conventional induction motor is arranged in an endless loop.[1]

Despite their name, not all linear induction motors produce linear motion; some linear induction motors are employed for generating rotations of large diameters where the use of a continuous primary would be very expensive.

As with rotary motors, linear motors frequently run on a three-phase power supply and can support very high speeds. However, there are end-effects that reduce the motor's force, and it is often not possible to fit a gearbox to trade off force and speed. Linear induction motors are thus frequently less energy efficient than normal rotary motors for any given required force output.

LIMs, unlike their rotary counterparts, can give a levitation effect. They are therefore often used where contactless force is required, where low maintenance is desirable, or where the duty cycle is low. Their practical uses include magnetic levitation, linear propulsion, and linear actuators. They have also been used for pumping liquid metals.[2]

  1. ^ Ghaseminejad Liasi, Sahand (15 May 2015). "What are linear motors?". pp. 1–50. doi:10.13140/RG.2.2.16250.18887. Retrieved 24 December 2017.
  2. ^ "Bulletin of the Atomic Scientists". Educational Foundation for Nuclear Science, Inc. 1 September 1973 – via Google Books.