Asynchronous Motors – Principle of Operation

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In asynchronous electric motors the permanent magnet is suspended on a metal disk, secured by a pin in an iron bearing. The magnetic flux produced by the permanent magnet flows through the magnetic circuit series consisting of the permanent magnet, the air gap and the iron plate.

The disk under the magnet also rotates when the permanent magnet rotates. The disk accompanies the rotational movement of the permanent magnet due to the circulation of induced currents and these currents are induced due to the relative movement between the disk and the permanent magnet.

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Induced currents can produce, according to Lenz’s law, a magnetic south pole on the disk under the permanent magnet’s north magnetic spinning pole, as well as a magnetic north pole on the disk under the rotating magnetic south pole of the permanent magnet.

As the magnet rebuilds its movement relative to the disk, the induction of parasitic currents and magnetic poles with opposing polarities will continue. In this way the disk rotates in the same direction as the permanent magnet, but must rotate at a slower speed so that we have a relative velocity between the permanent magnet and the metal disk.