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Single  phase induction motor Single  phase induction motor

Single phase induction motor - PowerPoint Presentation

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Single phase induction motor - PPT Presentation

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

phase motor winding induction motor phase induction winding stator single rotor starting actual construction additional fans capacitor principle direction

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Presentation Transcript

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

© Nafees Ahamad Slide3

Actual 1-phase induction motor

Ceiling fans: Internal structure

Cage rotor

© Nafees Ahamad Slide4

Actual 1-phase induction motor

Other single phase induction motor:

© Nafees Ahamad Slide5

Actual 1-phase induction motor

Some other single phase induction motor:

© Nafees Ahamad Slide6

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.

© Nafees Ahamad Slide7

Construction…

Schematic Diagram of stator

L

N

Frame

Or

Yoke

Core

(Laminated)

1

phase Stator

winding

Stator Teeth

© Nafees Ahamad Slide8

Construction…

Rotor Squirrel cage rotor is usedAluminum

bus bars shorted together at the ends by two aluminum

rings.

© Nafees Ahamad Slide9

Construction…

Al or Cu bars

End Ring

End Ring

Squirrel cage rotor

© Nafees Ahamad Slide10

Construction…

Constructional representation of rotor and stator:

© Nafees Ahamad Slide11

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.

© Nafees Ahamad Slide12

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.

© Nafees Ahamad Slide13

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’.

© Nafees Ahamad Slide14

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.

© Nafees Ahamad Slide15

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.

© Nafees Ahamad Slide16

Principle..

© Nafees Ahamad Slide17

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

© Nafees Ahamad Slide18

Double Revolving Field Theory …

1-pase supply

L

N

Stator field winding

 

 

Main switch

Forward

flux

Backward

flux

 

 

Rotor

N

© Nafees Ahamad Slide19

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

 

© Nafees Ahamad Slide20

Double Revolving Field Theory …

(using

eq

(1))

 

© Nafees Ahamad Slide21

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

© Nafees Ahamad Slide22

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.

© Nafees Ahamad Slide23

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.

© Nafees Ahamad Slide24

Thanks

© Nafees Ahamad