By Nafees Ahmed Asstt Prof EE Deptt DIT University Dehradun Actual 1phase induction motor Ceiling fans Actual 1phase induction motor Ceiling fans Internal structure Actual 1phase induction motor ID: 713968
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Slide1
Single Phase Induction Motor
By: Nafees Ahamad,Asstt. Prof., EE Deptt,DIT University, Dehradun
© Nafees Ahamad Slide2
Actual 1-phase induction motor
Ceiling fans
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Actual 1-phase induction motor
Ceiling fans: Internal structure
Cage rotor
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Actual 1-phase induction motor
Other single phase induction motor:
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Actual 1-phase induction motor
Some other single phase induction motor:
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Construction
Construction is similar as that of 3-phase squirrel induction motor A single phase induction motor has two main partsStator
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.
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Construction…
Schematic Diagram of stator
L
N
Frame
Or
Yoke
Core
(Laminated)
1
phase Stator
winding
Stator Teeth
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Construction…
Rotor Squirrel cage rotor is usedAluminum
bus bars shorted together at the ends by two aluminum
rings.
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Construction…
Al or Cu bars
End Ring
End Ring
Squirrel cage rotor
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Construction…
Constructional representation of rotor and stator:
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Construction
Shaft: Mild steel shaft with maximum breaking strength.
Bearings:
Ball bearing or roller bearing.
It is used in
vacuum cleaner, fans, washing machine, centrifugal pump, blowers, washing machine, small toys etc.
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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 conductorsNow 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.
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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
in
such machine is given initial start by hand or otherwise in either direction, then motor starts rotating in that direction.
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
auxiliary
winding.
*Above
peculiar behavior can
also be
explained by ‘Double filed revolving theory’.
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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.
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Principle…
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.
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Principle..
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Double Revolving Field Theory
This theory is based on the idea that pulsating field (induced in 1-phase IM) can be resolved into two components of half its amplitudes & rotating in opposite direction with synchronous speed (This is called as Ferrari’s principle).This is shown by a diagram on next slide
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Double Revolving Field Theory …
1-pase supply
L
N
Stator field winding
Main switch
Forward
flux
Backward
flux
Rotor
N
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Double Revolving Field Theory …
Let rotor is rotating in clockwise direction One flux is called as forward flux (clockwise) while other is known as backward flux (anti-clockwise).So slip w.r.t forward flux
So slip w.r.t
backward
flux
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Double Revolving Field Theory …
(using
eq
(1))
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Double Revolving Field Theory …
So now torque-slip characteristics of 1-phase induction motor will be
s = 0
s = 1
s = 2
Torque
Torque due to forward flux
Torque due to forward flux
Net Torque
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Double Revolving Field Theory …
It is clear from the previous figure that net torque is zero at time of starting ( at s = 1). Hence 1-phase induction motor will not be self starting. If a push is given in either direction, it will results in net torque and motor will rotating in that direction.
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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.
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Thanks
© Nafees Ahamad