Single phase induction motor
By: Nafees Ahmed,
Asstt. Prof., EE Deptt,
DIT University, Dehradun
Actual 1-phase induction motor
 Ceiling fans
Actual 1-phase induction motor
 Ceiling fans: Internal structure
Actual 1-phase induction motor
 Ceiling fans: Internal structure
Actual 1-phase induction motor
 Ceiling fans: Cage rotor
Actual 1-phase induction motor
 Other single phase induction motor:
Actual 1-phase induction motor
 Other single phase induction motor:
Actual 1-phase induction motor
Construction
 Construction is similar as that of 3-phase squirrel
induction motor
 A single phase induction motor has two main parts
 Stator
 Similar to 3-phase induction motor
 consisting of a steel frame that supports a hollow,
Laminated cylindrical core
 core, constructed from stacked laminations (why?), having
a number of evenly spaced slots, providing the space for
the stator winding
Construction
stator
Construction
rotor
Squirrel cage rotor is used
aluminum bus bars shorted together at
the ends by two aluminum rings.
Construction
Shaft
End rings
Rotor
Aluminum
or copper
bars
Construction
 Constructional representation of rotor and stator:
Construction
Shaft: Should withstand maximum
breaking strength
Bearing: Roller or ball bearing
It is used in vacuum cleaner, fans,
washing machine, centrifugal pump,
blowers, washing machine, small toys
etc.
Principle:
 When stator winding is fed from a single phase supply,
an alternating (pulsating) field is produced.
 Due to this alternating flux an alternating EMF (current) is
induced in the rotor conductors
 Now when a current carrying conductor is place in
magnetic filed it experiences a force.
 But after each half cycle the direction of induced
current is change and hence the direction of force
(torque) is changed after each half cycle.
Principle:
 So pulsating flux acting on stationary squirrel cage rotor can’t produce
rotation and therefore 1-phase induction motor is not self starting.
 However, if the rotor o such machine is given initial start by hand or
otherwise in either direction, then motor starts rotating in that direction.
 Above peculiar behavior can be explained by
 Double filed revolving theory
 To make it self-starting, it can be temporarily converted into a two-phase
motor while starting. This can be achieved by introducing an additional
'starting winding' also called as auxillary winding.
Principle:
 Hence, stator of a single phase motor has two windings: (i) Main
winding and (ii) Starting winding (auxiliary winding). These two
windings are connected in parallel across a single phase supply
and are spaced 90 electrical degrees apart. Phase difference of 90
degree can be achieved by connecting a capacitor in series with
the starting winding.
 Hence the motor behaves like a two-phase motor and the stator
produces revolving magnetic field which causes rotor to run. Once
motor gathers speed, say upto 80 or 90% of its normal speed, the
starting winding gets disconnected form the circuit by means of a
centrifugal switch, and the motor runs only on main winding.
Principle:
Type of single phase induction motors
 The single phase induction motors are made self starting by
providing an additional flux by some additional means(
Additional winding ). Now depending upon these additional
means the single phase induction motors are classified as:
 Resistance start induction motor
 Capacitor start induction motor
 Capacitor start capacitor run induction motor.
 Permanent capacitor motor
 Shaded pole induction motor.