6-Induction Motor

2. Principle of operation of the asynchronous machine

Creating a rotating field

  • If three identical coils placed at 120 ° are fed by a three-phase AC voltage:

  • A magnetized needle, placed in the centre, is rotated; so there is a creation of a rotating field.

  • The needle is replaced by a metal disc made of aluminium or copper. It is driven in the same direction as the magnetic needle.

  • If two of the three three-phase power leads are reversed, the needle or disc rotates in the opposite direction.

Principle

The three AC fields produced by the three-phase-fed coils are composed to form a rotating field. The rotating magnetic field creates induced currents in the metal disk; these, according to Lenz's law, oppose the cause that gave rise to them, and cause a magneto motive force that drives the disk in rotation.

The part containing the coils creating the magnetic field is called "STATOR". The moving part under the influence of the magnetic field is called "ROTOR".

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