In the previous, i.e. first, lesson of this module, the formation of rotating magnetic
field in the air gap of an induction motor (IM), has been described, when the three-phase
balanced winding of the stator is supplied with three-phase balanced voltage. The
construction of the stator and two types of rotor
squirrel cage and wound (slip-ring)
one, used for three-phase Induction motor will be presented. Also described is the
principle of operation, i.e. how the torque is produced.
Three-phase induction motor, cage and wound (slip-ring) rotor, synchronous
and rotor speed, slip, induced voltages in stator winding and rotor
After going through this lesson, the students will be able to answer the following
How would you identify the two types (cage and wound, or slip-ring) of rotors in
three-phase induction motor?
What are the merits and demerits of the two types (cage and wound, or slip-ring) of
rotors in IM?
How is the torque produced in the rotor of the three-phase induction motor?
How does the rotor speed differ from synchronous speed? Also what is meant by the
Construction of Three-phase Induction Motor
This is a rotating machine, unlike the transformer, described in the previous module,
which is a static machine. Both the machines operate on ac supply. This machine mainly
works as a motor, but it can also be run as a generator, which is not much used.
rotating machines, it consists of two parts
stator and rotor. In the stator (Fig. 30.1), the
winding used is a balanced three-phase one, which means that the number of turns in
each phase, connected in star/delta, is equal. The windings of the three phases are placed
(electrical) apart, the mechanical angle between the adjacent phases being
], where p is no. of poles. For a 4-pole (p = 4) stator, the mechanical angle
Version 2 EE IIT, Kharagpur