173x Filetype PPT File size 2.26 MB Source: faculty.yu.edu.jo
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. 2 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. 3 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. 4 5 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. 6
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