MOTOR
1. Single Phase Induction Motor
ü Operation
ü Construction
ü Method Of Starting
2. Three Phase Induction Motor
· Operation
· Construction
· Torque Speed Charactercitic
3. Motor
· Operation
· Construction
· Method Of Stating
4. Three Phase Squiral Cage Motor
· Operation
· Construction
· Mthod Of Stating
1. Single Phase Induction Motor
Operation
It Has Two Main Parts
ü Rotor
ü stator
stator
· Stator Is A Stationary Part Of Induction Motor.
· A Single Phase Ac Supply Is Given To The Stator Of Single Phase Induction Motor.
· The Stator Of The Single Phase Induction Motor Has Laminated Stamping To Reduce Eddy Current Losses On Its Periphery.
· The Slots Are Provided On Its Stamping To Carry Stator Or Main Winding.
synchronous speed Ns
f = supply voltage frequency,
P = No. of poles of the motor
Rotor
· It Is A Rotating Part Of Induction Motor.
· It Is Connected To The Mechanical Load Through The Shaft.
· It Is A Cylindrical In Shape And Has Slots All Over Its Periphery. The Slots Are Not Made Parallel To Each Other But Are Bit Skewed As The Skewing Prevents Magnetic Locking Of Stator And Rotor Teeth And Makes The More Smooth And Quieter.
· The Rotor Conductors Are Permanently Shorted By The Copper Or Aluminum Rings Called The End Ring.
Construction
Firstly The Single Phase Induction Motors Are Mostly Provided With Concentric Coils. As The Number Of Turns Per Coil Can Be Easily Adjusted With The Help Of Concentric Coils, The Mmf Distribution Is Almost Sinusoidal.
METHOD OF STATING
· When Single Phase Ac Supply Is Given To The Stator Winding Of Single Phase Induction Motor, The Alternating Current Starts Flowing Through The Stator Or Main Winding.
· This Alternating Current Produces An Alternating Flux Called Main Flux. This Main Flux Also Links With The Rotor Conductors And Hence Cut The Rotor Conductors.
· According To The Faradays Law Electromagnetic Induction Emf Gets Induced In The Rotor. As The Rotor Circuit Is Closed One So, The Current Starts Flowing In The Rotor Starts Flowing In The Rotor.
· This Current Is Called The Rotor Current.
· This Rotor Current Produces Its Own Flux Called Rotor Flux.
· Since This Flux Is Produced Due To Induction Principle So, The Motor Working On This Principle Got Its Name As Induction Motor.
· Now There Are Two Fluxes One Is Main Flux And Another Is Called Rotor Flux.
· These Two Fluxes Produce The Desired Torque Which Is Required By The Motor To Rotate.
2. THREE PHASE INDUCTION MOTOR
OPERATION
The 3-P Induction Motor A Classified
· Squirrel cage
· Slip ring or wound
1. The three-phase stator winding is connected to a three-phase supply.
2. Currents flow in the stator winding, producing a rotating mmf and flux density.
3. The stator flux density rotates at synchronous speed.
4. The magnetic field passes conductors on the rotor and induces a voltage in those conductors.
5. Since the conductors are short circuited, current flows in the rotor conductors.
6. The rotor currents produce a second rotor magnetic field, which acts to oppose the stator magnetic field and also rotates at synchronous speed.
7. With two magnetic fields rotating at constant speed, a torque is induced.
8. The rotor flux density will lag the stator flux density (flux density lags current by 90° electrically), therefore the torque will be in the same direction as the rotation of the magnetic fields.
9. The torque accelerates the rotor until synchronous speed is reached, at which time there is no relative motion between the conductors and the stator flux density. Since the relative velocity is zero, the induced voltage, rotor currents and flux density fall to zero and torque is also zero.
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