TABLE OF CONTENTS The direct-current (dc) and synchronous motors we have discussed thus far have one thing in common: both are the doubly-fed type. These motors have direct current in their field windings and alternating current (ac) in their armature windings. Since the electrical power is delivered directly to the armature of a dc motor via a commutator, it can also be referred to as a conduction motor.
We now consider a motor in which the rotor receives its power not by conduction but by induction and is therefore called an induction motor. A winding that receives its power exclusively by induction constitutes a transformer. Therefore, an induction motor is a transformer with a rotating secondary winding. From the above discussion, the following must be evident:
An induction motor is a singly-fed motor. Therefore, it does not require a commutator, slip-rings, or brushes. In fact, there are no moving contacts between the stator and the rotor. This results in a motor that is rugged, reliable, and almost maintenance free.
The absence of brushes eliminates the electrical loss due to the brush voltage drop and the mechanical loss due to friction between the brushes and commutator or the slip-rings. Thus, an induction motor has a relatively high efficiency.
An induction motor carries alternating current in both the stator and the rotor windings.
An induction motor is a rotating transformer in which the secondary winding receives energy by induction while it rotates.
There are two basic types of induction motors: single-phase induction...
