Induction Motor:

· Induction motor is basically an AC motor; which requires an alternating voltage in order to operate it properly.

· An Induction motors is having and two important parts

A. Stator

B. Rotor

· The Stationary frame is called as Stator and rotating armature is nothing but anrotor.

· Stator is similar to generator which is made up of large number of stampings which are 0.4 to 0.5 mm thick

· The air gap between Stator and rotor is between 0.4 to 4mm.

· These stampings are having slots in order to receive the stator windings.

· Basic parts are explained below so just have a look so that it will be easier to us to understand induction motors:

§ Frame: Its function is to provide mechanical support to the entire body of the Motor.its like yoke which is used in DC also contains the stator winding

§ Air Gap:it provides space for the rotating magnetic field between stator and rotor

§ Fan: The fan rotates with the rotor and its function is to cool down the motor

§ Slip Rings: The Motor winding terminal windings are permanently connected to the slip rings. The sliprings are continuously in contact with three brushes which are press against the slip rings.

· The stator winding is used to produce the magnetic field in the air gap in between the stator and the Rotor.

· The rotor is not connected to any external supply .

· Current flows through the rotor due to the principal of induction hence it is named as an induction Motor

Rotating Magnetic Field:-

· Induction motor works on the principle of Rotating magnetic Field (RMF) which is produced by the stator winding of induction motor in the air gap between the stator and the rotor.

· Stator is basically a three phase stationary winding which will be either star or delta in type.

· If AC Supply will be given to stator windings Line CurentsViz IR, IY and IB starts flowing in it with an angle of 120 degree w.r.t each other.

· Each line will produce an Sinusoidal flux in the air gap which are having same same frequency as that of the line Currents vis 50Hz and they are also having phase shift of 120 degree with each other.

· Let’s assume the flus Produced by the line Current:

IR be ΦR, IY be ΦY and IB be ΦB

Mathematically it is given as:-

Φ R= Φ msint ῳt=Φ msinθ

Φ Y=Φ msin( ῳt- )=Φ msin(θ - )&

Φ B=Φ msin( ῳt- )=Φ msin(θ - )

Direction of RMF:

· The direction of RMF depends on the phase sequence of AC supply being connected to the stator winding

· The RMF will rotates in Clockwise direction if R,Y and B will be in normal sequence but if we interchange the two of the phases in of the supply then the direction will be revered viz it will rotate in anticlock wise direction as:-