2. Introduction
• An induction motor is an AC electric motor in
which the electric current in the rotor needed
to produce torque is obtained
by electromagnetic induction from
the magnetic field of the stator winding.
• This motor is also called as asynchronous
motor because it runs at a speed less than its
synchronous speed.
3. Types of Induction Motor
• Single Phase IM
For low power applications in homes,
offices, shops, and small factories
• Three Phase IM
For High power applications in large scale
industries and projects
• High Phase IM (More than 3 phase)
7. Important parts of IM
• Stator is the stationary portion of
the motor and delivers a rotating
magnetic field to interact with the
rotor.
• One or more copper windings make
up a "pole" within the stator, and
there is always an even number of
poles within a motor.
• The electric current alternates
through the poles, resulting in a
rotating magnetic field.
8. Important parts of IM
• Rotor is the central
component of the motor
which rotates.
• The speed of rotation
depends on frequency of
supply.
• The interaction of the
magnetic fields in the
stator and rotor results
in a mechanical torque
of the rotor.
9. Important parts of IM
• Motor shaft is fixed within
the rotor, and rotates with
it.
• The shaft extends outside
of the motor casing, and
allows a connection to an
outside system to transmit
the rotational power.
• The shaft is sized to the
amount of torque the
motor puts out to avoid
breaking the shaft.
10. Important parts of IM
• The rotor shaft is held in place by bearings at
either end of the motor casing. The bearings
minimize the friction of the shaft connection
to the casing, increasing the efficiency of the
motor.
13. Working of an Induction Motor
How does an Induction Motor work _.mp4
rotating field animation in AC machine.mp4
14. Generation of rotating magnetic field
• A three-phase balanced winding in the stator of the
Induction motor (IM) is shown in below.
• In a three-phase balanced winding, the number of turns
in three windings, is equal, with the angle between the
adjacent phases, say R & Y, is 120 ̊ (electrical).
• Same angle of 120 ̊(elec.) is also between the phases, Y
& B.
15. Generation of rotating magnetic field
• A three-phase balanced voltage, with the
phase sequence as R-Y-B, is applied to the
above winding.
• In a balanced voltage, the magnitude of the
voltage in each phase is equal, with the phase
angle of the voltage between the adjacent
phases, say R & Y, being120°.
16. Generation of rotating magnetic field
The three phases of the stator winding
(balanced) carry balanced alternating
(sinusoidal) currents
17. Generation of rotating magnetic field
Three pulsating mmf waves are set up in the air-
gap, which have a time phase difference of 120 ̊
from each other.
These mmf’s are oriented in space along the
magnetic axes of the phases, R, Y & B
21. Types of windings
• Concentrated Winding: All conductor are
concentrated in one slot under a pole. There is
only one slot available for winding under one
pole.
In short, if No. of slot = No. of pole it is called
concentrated winding.
• Distributed Winding: If no. of slot is more
than no. of pole which means winding is
distributed in many slot under a pole.
24. Pros and Con of distributed and
concentrated winding
• Induced emf in concentrated winding is greater
than distributed.(But why? explained later)
• Harmonic or noise in distributed winding is lesser
than concentrated winding.(that's why we
normally use distributed winding in expense of
lesser emf).So, improved waveform.
• Less armature reaction in distributed winding.
• Full utilization of the armature iron and copper in
distributed winding.
• Distribution of winding adds to rigidity and
mechanical strength.
25. Terms
• Coil span or coil pitch=No. of slots/No. of
poles for full pitch
• Pole pitch
Indicates Pole pitch=180 degrees
electrical
28. Points to remember
• In full pitched coil, the phase angle between
the emfs induced in two coil sides is exactly
180o (electrical).
• In short pitched coil, the induced emf of two
coil sides is vectorically added to get, resultant
emf of the coil.
• In short pitched coil, the phase angle between
the emfs induced in two opposite coil sides is
less than 180o(electrical).
29. • Pitch factor (Kp)
Pitch factor is the measure of resultant emf of
short pitched coil in comparison with resultant
emf of full pitched coil.
31. Important points
• If all the coil side of any one phase under one
pole are bunched in one slot, the winding
obtained is known as concentrated winding.
• The total emf induced is equal to arithmetic
sum of the emfs induced in all the coils of one
phase under one pole.
32. Important Points
• But in practical cases, for obtaining smooth
sinusoidal voltage wave form, armature
winding of alternator is not concentrated but
distributed among the different slots to form
polar groups under each pole.
• In distributed winding, coil sides per phase are
displaced from each other by an angle equal
to the angular displacement of the adjacent
slots.
34. Distribution or breadth factor (Kd)
• The ratio of the phasor sum of the emfs
induced in all the coils distributed in a number
of slots under one pole to the arithmetic sum
of the emfs induced(or to the resultant of
emfs induced in all coils concentrated in one
slot under one pole) is known as breadth
factor (K Distribution Factor b) or distribution
factor
39. Winding factor
The winding factor for a specific winding
expresses the ratio of flux linked by that winding
compared to flux that would have been linked
by a single-layer full-pitch non-skewed integer-
slot winding with the same number of turns and
one single slot per pole per phase
40. Important point
• The winding factor Kw can generally be
expressed as the product of three factors, the
pitch factor Kp (sometimes also called coil-
span or chording factor), the breath
coefficient or distribution factor Kd, and the
skew factor Ks.
Kw=Kp*Kd*Ks
41. Summary
• The pitch factor (Kp) reflects the fact that windings are
often not fully pitched, i.e. the individual turns are
reduced in order to decrease the length of the end-
turns and do not cover a full pole-pitch (also called
chorded).
• The distribution factor (Kd) reflects the fact that the
winding coils of each phase are distributed in a number
of slots. Since the emf induced in different slots are not
in phase, their phasor sum is less than their numerical
sum.
• The skew factor (Ks) reflects the fact that the winding
is angularly twisted, which results in an angular spread
and reduced emf.
