A

SEMINAR ON

“INDUCTION MOTOR”

BACHELOR OF TECHNOLOGYIN

ELECTRICAL & ELECTRONICS ENGINEERINGSUBMITTED

BY

PANKAJ CHAUDHARY R.N. - 24823

UNDER THE SUPERVISION OF

ARUNESH DUTT (H.O.D)

NEHRU GRAM BHARATI UNIVERSITY, ALLAHABAD

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

SANJAY GANDHI INSTITUTE OF ENGINEERING & TECHNOLOGY

INTRODUCTION

CONSTRUCTION

PRINCIPLE OF OPERATION

*DOUBLE REVOLVING FIELD THEORY

SQUIRREL CAGE ROTOR

INDUCTION MOTOR SPEED

THE SLIP

STARTING TORQUE

APPLICATION

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The induction motor is one of ac machine, in which there are alternating currents in both stator and

rotor windings. The alternating current is supplied directly to the stator winding and by induction, i.e.

transformer action, to the rotor winding.

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The single-phase motor stator has a laminated iron core with two windings arranged perpendicular

- One is the main and

- The other is the auxiliary winding or starting

winding.

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A single phase induction motor has two main parts namely stator (the one which is stationary) and rotor (the one which is rotating).

The stator winding is connected across a single phase ac supply . The ac supply produces a rotating magnetic field in the air gap between the stator and rotor. The field rotates at a speed called synchronous speed and it is denoted by Ns.

It is mathematically expressed as,

Ns = 120f/p rpm

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The induction motor actually rotates at a speed which is slightly less than the synchronous speed.

The rotor is said to be squirrel cage type. As the construction of rotor appears to be like the squirrel’s cage, the name squirrel cage rotor has been used.

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A single phase ac supply is connected to the stator winding. This forces an alternating current through the stator winding . This current produce an alternating flux in the air gap between the stator and rotor.

The induced voltage ,a current start flowing through the conductors. This current will the produce its own flux called as the rotor flux. The main flux produce by the stator winding interacts with the rotor flux to produce the torque.

It is important to note that the single phase induction motor are not self starting, like the dc motors

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A single phase ac supplies the main winding that produces a pulsating magnetic field.

The pulsating field is divided a forward and reverse rotating field.

Motor is started in the direction of forward rotating field this generates small (5%) positive slip.

Spos =(nsy –nm)/ nsy

Reverse rotating field generates a larger ( 1.95 %) negative

slip. Sneg =(nsy + nm)

Each of the rotating field induces a voltage in the rotor , which derives currents and produces torque.

DOUBLE REVOLVING FIELD THEORY-

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The bars and end rings together look like a cage and hence such a rotor is called a cage rotor or a squirrel cage rotor.

The rotor consists of copper or aluminium bars which are permanently short circuited at both the ends using the conducting rings called end rings.

So, the IM will always run at a speed lower than the synchronous speed

The difference between the synchronous speed and the motor speed is called the Slip speed.

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slip sync mn n n

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sync m

sync

n ns

n

Where s is the slip

* Slip may be expressed as a percentage by multiplying the above eq. by 100, notice that the slip is a ratio and doesn’t have units.

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The single phase induction motor starting torque is zero because of the pulsating single phase magnetic flux

Two perpendicular coils that have current 90⁰ out of phase can generated the necessary rotating magnetic fields which start the motor.

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The single phase induction motor of application are-

-Fans,

- Refrigerators,

- Washing machines

- Drills

-Compressors

- Centrifugal Pumps, etc

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