Tuesday, June 7, 2011

Construction of Three Phase Induction motor

Basically the induction motor consists of two main parts, namely
  1. The part i.e. three phase windings,which is stationary called stator.
  2. The part which rotates and is connected to the mechanical load through shaft called rotor.
        The conversion of  electrical power to mechanical power takes place in a rotor. Hence rotor develops a driving torque and rotates.

       The stator has a laminated type of construction made up of stampings which are 0.4 to 0.5 mm thick. The stampings are slotted in its periphery to carry the stator winding. The stampings are insulated from each other. Such a construction essentially keeps the iron losses to a minimum value. The number of stampings are stamped together to build the stator core. The built up core is then fitted in a casted or fabricated steel frame. The choice of material for the stampings is generally silicon steel, which minimises the hysteresis loss. The slots in the periphery of the stator core carries a three phase winding, connected either in star or delta. This three phase winding is called stator winding. It is wound for definite number of poles. This winding when excited by a three phase supply produces a magnetic rotating field as discussed earlier. The choice of number of poles depends on the speed of the rotating magnetic field required. The radial ducts are provided for the cooling purpose. In some cases, all the six terminals of three phase stator winding are brought out which gives flexibility to the user to connect them either in star or delta. The Fig. 1 shows a stator lamination.
Fig.  1 Stator lamination

       The rotor is placed inside the stator. The rotor core is also laminated in construction and uses cast iron. It is cylindrical, with slots on its periphery. The rotor conductors or winding is placed in the rotor slots. The two typed of rotor constructions which are used for induction motors are,
  1. Squirrel cage rotor and
  2. Slip ring wound rotor  
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