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    BEE Experiment-10

    Uploaded by

    Khushee Singh

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    BEE Experiment-10

    Uploaded by

    Khushee Singh
    6 views3 pages

    Copyright

    © © All Rights Reserved

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    PDF, TXT or read online from Scribd

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    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    6 views3 pages

    BEE Experiment-10

    Uploaded by

    Khushee Singh

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 3

    Experiment-10

    Object- Demonstration of cut section of Three Phase Induction Motor.

    Apparatus Required- cut section model of Three Phase induction motor.

    Theory- A three phase induction motor consists of two main parts namely Stator and Rotor.

    1. Stator- It is outer body of the motor. It has three main parts.

    (A). Outer frame- Its function is to support the stator core and to protect the inner parts of the
    machine. For small machines the frame is casted but for large machine it is fabricated. To place the
    motor on foundation, feet are provided in the outer frame.

    (B). Stator Core- The stator core is to carry the alternating magnetic field which produces hysteresis
    and eddy current losses. Therefore core is built up of high grade silicon steel stampings. The stampings
    are assembled under hydraulic pressure and are keyed to the frame. Each stamping is insulated from
    each other with a thin varnish layer. The thickness of the stamping varies usually from 0.3mm to 0.5mm
    slots are punched on the inner periphery of the stampings, as shown in figure to accommodate stator
    winding.

    (C). Stator Winding- The stator core carries a three phase winding which is usually supplied from a
    three phase supply system. The six terminals of the windings (two of each phase) are connected in the
    terminal box of the machine. The stator of the motor is wound for definite number of poles, the exact
    number being determined by the requirement of speed. It will be seen that greater the number of poles,
    the lower the speed and vice versa, since Ns directly proportional to the I/P (therefore Ns= 120f/p), the
    three phase winding may be connected in star or delta externally through a stator.

    2. Rotor- It is the rotating part of the motor. There are two types of rotors, which are employed in three
    phase induction motor.

    (A). Squirrel cage rotor- The motors employing this type of rotor are known as squirrel cage induction
    motors. Most of the induction motors are of these types because of simple and rugged construction of
    rotor. A squirrel cage rotor consists of a laminated cylindrical core having semi closed circular slots at
    the outer periphery. Copper or aluminum rings, called short circuiting rings. Thus the rotor winding is
    permanently short circuited and it is not possible to add any external resistance in the rotor circuit.
    The rotor slots are usually not parallel to the shaft but are skewed. Skewing of rotor has the following
    advantages.
    (I). It reduces humming thus ensuing quit running of a motor.
    (II). It results in a smoother torque curves for different position of the rotor.
    (III). It reduces the magnetic locking of the stator and rotor.
    (IV). It increases the rotor resistance.
    (B). Phase Wound Rotor- Phase wound rotor is also called slip ring rotor and the motors employing
    this type of rotor are known as phase wound or slip ring induction motors. Slip ring rotor consists of a
    laminated cylindrical core having semi closed slots at the outer periphery and carries a 3 phase insulated
    winding. The rotor is wound for the same number of poles as that of stator. The three phase three
    copper slipping fixed on the shaft.
    In this case, depending upon the requirement any external resistance can be added in the rotor circuit.
    In this case rotor is skewed.
    A mild steel shaft is passed through the centre of the rotor and is fixed to it with key. The purpose of
    shaft is to transfer mechanical power.

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