AC Motors are one of two types of electric motors.  AC Motors derives its name from the alternate current used to drive it.  The other type of electric motor is of course the DC Motor, being of direct current.  AC Motors fall into a further two categories known as synchronous AC Motors and asynchronous/induction AC Motors. 

1.  Synchronous AC Motors 

In a synchronous AC Motor, the current passes through a magnetic field in the rotors at the same rate the alternating current does.  This results in no slip.  As we all know, the main function of the stator in an AC Motor is to set up a rotating or oscillating field.  In an AC Motor that is synchronous, the rotor’s magnetic poles are fixed and the AC Motor’s speed is determined by the number of poles in the AC Motor and the frequency of the current supplied to it.

2.  Induction AC Motors

In an induction AC Motor, the stator’s oscillating magnetic field causes or induces current in the rotor.  Induction AC Motors rely on the rotor turning slower than the rotation of the stator fields.  This can be attributed to the fact that as the speed of the rotor approaches the speed of the stator field, the torque decreases.  This difference is known as slip and is what makes the induction AC Motor operates.  Two types of rotors are common in induction AC Motors; the squirrel cage rotor and the wound rotor.  The squirrel cage type resembles a hamster wheel and the rotor is practically self-contained.  These types of rotors are used for AC Motors smaller than one horsepower.  The wound rotor consists of insulated coils of wire.  They are not permanently short-circuited but are connected in regular succession to form a defined polar area having the same number of poles as the stator.

2.1 Single-Phase Induction AC Motors

The two most common types of AC Motors are single-phase and three-phase.  Single-phase AC Motors can be subdivided into split-phase and commutator.  Split-phase AC Motors can be further subdivided into resistance-start, reactor-start, split-capacitor and capacitor-start AC Motors.  Commutator AC Motors are subdivided into two groups: series and repulsion, while these are subdivided even further and all are modified to produce the necessary starting torque.

2.2 Three-Phase Induction AC Motors

Three-phase induction AC Motors does not need centrifugal switches or capacitors, seeing as they generate their own rotating magnetic torque.  These types of AC Motors are used for machine tools, fans, air compressors, air conditioning equipment, and industrial pumps.

EP Normand | AC Drives | DC Drives