Induction Motor
      • Comparing with synchronous motor No dc field 
         current is required to run the machine.
      • Instead, amortisseur windings are installed in the 
         rotor. 
      • The machine is called “Induction” because the 
         rotor voltage is induced in the rotor windings 
         rather than physically connected by wires.
      • It is possible to use an induction machine as motor 
         or generator, but there are many disadvantages to 
         use it as generator.    
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       Induction Motor Components  
   1) Stator: Consisting of a steel frame 
      that supports a hollow, cylindrical 
      core of stacked laminations. Slots on 
      the internal circumference of the 
      stator house the stator winding
   2) Rotor: There are two different types 
      of induction motor rotor:
      Squirrel cage rotor (Cage rotor):
      Consists of series of conducting 
      bars laid into slots carved in the 
      face of rotor and shorted at either 
      end by large shorting rings.
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     Wound rotor IM
      •A wound rotor has a 3-phase 
      winding, similar to the stator 
      winding.
      •The rotor winding terminals are 
      connected to three slip rings 
      which turn with the rotor. The slip 
      rings/brushes allow external 
      resistors to be connected in series 
      with the winding.
      •The external resistors are mainly 
      used during start-up under normal 
      running conditions the windings 
      short circuited externally.
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              Induction  Motors Operation 
                            Principle
      1)   The three-phase stator is supplied by balanced 
           three-phase voltage that drives an AC 
           magnetizing current through each phase 
           winding.
      2)   The magnetizing current in each phase 
           generates a pulsating AC flux.  
      3)   The total flux in the machine is the sum of the 
           three fluxes.
      4)   The summation of the three AC fluxes results 
           in a rotating flux, which turns with constant 
           speed and has constant amplitude. 
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