Electrical machines miscellaneous

Electrical machines miscellaneous

Easy Questions
Moderate Questions

Electrical Machines

Electrical machines miscellaneous
  1. A 6-pole, 3-phase, 60 Hz induction motor runs at 1000 rpm developing maximum torque. Rotor resistance per phase is 1.2 ohms. Neglecting star tor impedance, for developing maximum torque, the external resistance to be connected in series with each rotor phase will be








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    For maximum torque,

    r2
    		 = x2
    s

    where, s =
    1200 − 1000
    		 = 0.2
    1000

    ∴   x2 =
    1.2
    		 = 6 ohms
    0.2

    Correct Option: B

    For maximum torque,

    r2
    		 = x2
    s

    where, s =
    1200 − 1000
    		 = 0.2
    1000

    ∴   x2 =
    1.2
    		 = 6 ohms
    0.2

  1. During no-load test, an induction motor draws power








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    For a synchronous machine with cylindrical rot or, magnetic circuit air -gap, and hence permeance, is same at every point. Whatever may be the rotor position, permeance seen by the rotor winding, or a winding on the startor remains constant and does not change with rotor position. Thus startor winding inductance L1, and rotor winding inductance L2 do not vary with respect to the rotor position angle θ.

    Correct Option: B

    For a synchronous machine with cylindrical rot or, magnetic circuit air -gap, and hence permeance, is same at every point. Whatever may be the rotor position, permeance seen by the rotor winding, or a winding on the startor remains constant and does not change with rotor position. Thus startor winding inductance L1, and rotor winding inductance L2 do not vary with respect to the rotor position angle θ.

  1. The shunt resistance circuit component obtained by no-load test of an induction motor is representation of








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    NA

    Correct Option: C

    NA

  1. Approximate value of the efficiency of a threephase induction motor running at a slip ‘s’ is given by








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    NA

    Correct Option: C

    NA

  1. Emf induced in the rotor of a 3-phase induction motor is proportional to the








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    NA

    Correct Option: A

    NA