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L35 3ph im

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  • 1. 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal 3 Phase Induction Motor - Introduction • Converts electrical power into mechanical power • Energy transfer by means of electromagnetic induction • Industrial & Commercial Applications  Pumping Systems  Refrigeration Systems  Compressors  Fans & Blowers  Industrial Drives
  • 2. Rotating Magnetic Field • 3 phase supply is given to a balanced 3 phase winding. • 3 alternating magnetic fluxes displaced mutually at 120 o is produced. 240)t(sinφφ 120)t(sinφφ tsinφφ maxB maxY maxR −= −= = ω ω ω
  • 3. Considering different instances of time: (i) At wt = 0 o The instantaneous fluxes are The resultant magnetic flux is 1.5 times peak value and Acting at 90 o to axis of reference. maxB maxY R φ866.0φ φ866.0φ 0φ += −= =
  • 4. (ii) At wt = 60 o The instantaneous fluxes are The resultant magnetic flux is 1.5 times peak value and acting at 30 o to axis of reference. i.e., rotated by 60 o w.r.t. previous angle 0φ φ866.0φ φ866.0φ B maxY maxR = −= +=
  • 5. Similarly if various instances are considered upto 360 o , it is seen that the resultant always has a magnitude of 1.5 times peak value and pointing in a direction at the angle of consideration. For every 360 o , the resultant magnetic field completes one rotation. Inference: When 3 phase currents flow in a balanced 3 phase winding, a rotating magnetic field is created which has constant magnitude, but rotates in synchronism with supply frequency. This speed of rotating magnetic field is called SYNCHRONOUS SPEED P f NS 120 =
  • 6. 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal Classification • Construction  Squirrel Cage, Slip Ring • Connection  Stator : Star, Delta  Rotor : Cage, Wound • Application  Constant Power, Constant Torque, Constant Speed,  Variable Torque - Variable Speed
  • 7. 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal Cross Sectional View Terminal Box Outer Frame Stator Cage Rotor Shaft Ball Bearings Supporting Base
  • 8. 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal Construction – Stator • Stator frame: Cast Iron, Mechanical Support to stator core • Stator core: Stack of cylindrical steel laminations • Stator Slots: Inner periphery, Windings Slots Stator Conductors Laminations Outer frame Stator Core Stator Slots Stator windings
  • 9. 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal Construction – Rotor • Types on the basis of rotor construction  Squirrel Cage Rotor  Slip Ring Rotor • Cylindrical Laminated core • Slots cutout on outer periphery • Conductors placed in slots
  • 10. 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal Construction – Squirrel cage Rotor • Skewed arrangement • Copper or Aluminum Bars • Conductors shorted by end rings • Closed rotor circuit Rotor bars End rings
  • 11. 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal Construction – Slip ring rotor • One end of Rotor conductors connected to each other (Star) Rotor External resistance Shaft • Other ends connected to slip rings • Slip rings in contact with brushes • Brushes connected to external resistance Slip rings Rotor Conductors Brush
  • 12. Representation 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal L1 – 15 3Ø Supply Stator Core Stator Slots Stator conductors Rotor conductors Rotor Slots Rotor CoreShaft

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