Induction motor GTU ALA

1. Induction Motor
By :
Rohan Kaushik 161310109051
Rohit Chavda 161310109052
Arpit Rawal 161310109050

2. Introduction
Induction Motors are the most commonly used motors in many applications.
These are also called as Asynchronous Motors, because an induction
motor always runs at a speed lower than synchronous speed.
Synchronous speed means the speed of the rotating magnetic field in the stator.
There basically 2 types of induction motor depending upon the type of input
supply –
(i) Single phase induction motor
(ii) Three phase induction motor.
Or they can be divided according to type of rotor –
(i) Squirrel cage motor
(ii) Slip ring motor or wound type

3. Construction
 Stator:
The stator is made up of various stampings with slots to carry three phase
windings. It is wound for a distinct number of poles. The windings are
geometrically divided 120 degrees separated.

4. Construction
 Rotor:
The rotor is the rotating part of the electromagnetic circuit. The
rotor comprises of a cylindrical laminated core with axially
placed parallel slots for carrying the conductors. Each slot
carries a copper, aluminium, or alloy.

5. Construction
Cutaway in a
typical wound-
rotor IM.
Notice the
brushes and the
slip rings
Brushes
Slip rings

6.  Alternating flux is produced around the stator winding due to AC supply.
This alternating flux revolves with synchronous speed. The revolving flux
is called as "Rotating Magnetic Field" (RMF).
 The relative speed between stator RMF and rotor conductors causes an
induced emf in the rotor conductors, according to the Faraday's law of
electromagnetic induction.
Principle of operation
 The rotor conductors are short circuited, and
hence rotor current is produced due to
induced emf. That is why such motors are
called as induction motors.
 Now, induced current in rotor will also
produce alternating flux around it. This rotor
flux lags behind the stator flux.

7. The Slip
sync m
sync
n n
s
n


As the cause of production of rotor current is the relative velocity between
rotating stator flux and the rotor, the rotor will try to catch up with the stator
RMF.
Thus the rotor rotates in the same direction as that of stator flux to minimize
the relative velocity. However, the rotor never succeeds in catching up the
synchronous speed.
s = 0 : if the rotor runs at synchronous speed
s = 1 : if the rotor is stationary
s is –ve : if the rotor runs at a speed above the synchronous speed
s is +ve : if the rotor runs at a speed below the synchronous speed
120 e
sync
f
n rpm
P


8. Frequency
 The frequency of the voltage induced in the rotor is given by
Where fr = the rotor current frequency (Hz)
P = number of stator poles
n = slip speed (rpm)
120
r
P n
f


( )
120
120
s m
r
s
e
P n n
f
P sn
sf
 


 

9. Application of Induction Motor
Applications of Single Phase Induction Motor
These are used in low power applications and widely used in domestic
applications as well as industrial. And some of those are mentioned below
• Pumps
• Compressors
• Small fans
• Mixers
• Toys
• High speed vacuum cleaners
• Electric shavers
• Drilling machines

10. Application of Induction Motor
Applications of Three Phase Induction Motor
• Lifts
• Cranes
• Hoists
• Large capacity exhaust fans
• Driving lathe machines
• Crushers
• Oil extracting mills
• Textile and etc.