Working principle of 3 phase induction motor

Written by michael logan
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Working principle of 3 phase induction motor
An image of one phase of a three-phase current supply powering three-phase motors. (electrical signals image by Albert Lozano from

Three-phase induction motors are simple and efficient motors that use the principles of magnetic attraction, alternating current and induction to cause a motor shaft to turn and exert force on a load.


The motor shaft is wrapped with coils of wire called windings. Current passing through the windings creates magnetic fields with positive and negative poles. Stationary windings inside the motor case create opposing magnetic fields. The attraction between the different field poles causes the shaft to turn.


An electric current is "induced" within a coil when it passes through a magnetic field. Induction motors take advantage of this by inducing current in the shaft windings instead of using brushes to transfer current.

Alternating Current

Alternating current changes direction 120 times per second. The voltage rises from 0 to a positive peak, declines towards 0 volts, reverses direction to decline to a negative peak and starts rising towards 0 again.

Three-Phase Current

Three-phase alternating current is supplied on three wires. The current in each wire is 120 degrees out of phase with the previous wire. When the voltage is at 0 on one wire, it is either positive or negative on the other two wires. Therefore, the motor is always receiving power and always exerting torque on the load.

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