3 phase induction motor contain two parts one is stator and another one is rotor . Lets we discuss in briefly.
3 phase induction motor
As shown in figure you can show stator core and stator winding .As a name indicates it’s static part.
stator core is made up of silicone steel which is laminated to reduce eddy current loss .main function of stator to provide easy path for a flowing flux.
Stator winding or field winding is placed in the stator slots which is supplied by three phase supply and produce rotating field .
Rotor is rotating part of a motor . Rotor mounted on a shaft and rotor is connected with mechanical load through shaft . Rotor have two types
- Squirrel cage type
- Wound type or slip ring type
As shown in figure squirrel cage rotor is cylinder of steel which contain laminated copper or aluminium bars . This bar is short-circuited by end ring .
current flow through this bars .As show in figure it looks like a squirrel cage that’s why this type of rotor name is squirrel cage rotor .
A motor contain squirrel cage type of rotor is called squirrel cage motor.
In industry this type of motor very famous because of their simple and rugged construction .speed-torque characteristics can be easily controlled by varying size of the bars .
It has only disadvantage is that low starting torque .in this type of rotor external resistance can not connected.
- Wound rotor type or slip ring type
Wound type rotor has cylindrical core .in this core copper winding are placed same like as stator winding .rotor winding terminal are taken out for a connection .
They connect with three slip rings which is mounted on a shaft .carbon brush are resting on this slip rings.
Variable resistor are connected through this slip rings ,At a starting time they provide low resistance .
when motor attain normal speed this three brush are short-circuited and motor runs like a squirrel cage motor.
in this type of rotor we get high starting torque.so whenever we have to required high starting torque then this type of rotor construction are used.
3 phase induction motor Principal :
Working of three phase induction motor depends on electro magnetic induction .Three phase induction motor is same like as transformer with rotating secondary.
Three phase induction motor convert electrical energy in to mechanical energy. It’s very famous in industrial uses.
3 phase induction motor Working :
Three phase stater winding connected with three phase supply then it will energized and they
produce rotating magnetic field ,This field is rotates at synchronous speed.This field cuts the rotor conductor which placed in rotor slots.
Because of relative speed between rotating field and stationary rotor conductor ,e.m.f is induced in rotor conductor according to Faraday’s law of electro magnetic induction .
Since rotor circuit is short-circuited and current start flowing through the rotor conductor.
According to Fleming’s rule mechanical force act on rotor conductor and rotor start to move in force direction .
Direction of force can be determined by Fleming’s rule .Rotor rotate lesser speed than synchronous speed .
different of synchronous speed and rotor speed is known as a slip .if slip becomes zero then rotor will rotate at synchronous speed .
- Simple and rugged construction
- Do not effect environmental conditions
- Constant speed motor
- a highly affected at a full load
- cheaper in cost
- low maintenance required
- During light load condition power factor of the motor drops
- Speed control is difficult
- Poor starting torque
- Operated under lagging power factor
Three phase induction motor applications
-Three phase induction motor are used in heavy load application like a
- Small fans
- High speed vacuum cleaner
- Electrical shavers
- Drilling machine
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