AC MOTORS

presented by

S.NARESH

( electrical engineer)

What is meant by motor?• A machine which converts electrical energy into mechanical energy is called as motor.• Motor is divided into two types depend upon the supply: AC MOTOR DC MOTOR

AC MOTOR

• A machine which converts electrical energy(alternating current)into mechanical energy is called ac motor.

Ac motor is divided into three types they are:Three phase motorsSingle phase motors

Special motors Types of three phase motors : induction motor synchronous motor The types and working of induction motor is discussed as follows.

TYPES OF THREE PHASE INDUCTION MOTOR.• Depend upon the rotor construction there are two types: SQUIRREL CAGE IM SLIP RING IM

Principle and working of induction motor• Induction motor works on the principle of mutual induction .• It is also called as rotating transformer.• It is a self starting one .• When the three phase supply is given to the stator the rotating

magnetic flux(RMF) is produced .(120f/p=Ns).• Depend upon the poles and frequency the rotating magnetic field

speed get varied.• For 50hz,4 pole the RMF speed is 1500rpm.

Contd…• This rotating magnetic field induces emf in the rotor due mutual

induction.• Due to rotor short circuit the starting current is more.so we need a

starter for induction motor.• According to the right hand thumb rule ,current carrying conductor

produces magnetic flux.• So rotor produces magnetic flux.

Contd…• Then both flux are added and cancelled each other depend upon the

polarity.• Then rotor exerts a force from high flux area to low flux area .• Likewise it starts to rotate.

SQUIRREL CAGE MOTOR• In this motor, rotor cannot have any windings. There is only a copper

or aluminum bars.• The conductor bars are short circuited by end rings.• And there no possibility to add any external resistance to rotor.• So starting current cannot be controlled and it lead to voltage sag.

SLIP RING OR WOUND MOTOR• In this motor ,rotor have three phase windings.• External resistance can be added to rotor conductor.• So, the starting current can be controlled.

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