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Polyphase Induction Motors - section-1
  1. A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor

    2. A.

     Will continue running burning its one phase
    B.

     Will continue running burning its two phase
    C.

     Will stop and carry heavy current causing permanent damage to its winding
    D.

     Will continue running without any harm to the winding

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  2. Star-delta starting of motors is not possible in case of

    3. A.

     Single phase motors
    B.

     Variable speed motors
    C.

     Low horse power motors
    D.

     High speed motors

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  3. In an induction motor the relationship between stator slots and rotor slots is that

    4. A.

     Stator slots are equal to rotor slots
    B.

     Stator slots are exact multiple of rotor slots
    C.

     Stator slots are not exact multiple of rotor slots
    D.

     None of the above

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  4. A 3-phase slip ring motor has

    5. A.

     Double cage rotor
    B.

     Wound rotor
    C.

     Short-circuited rotor
    D.

     Any of the above

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  5. Low voltage at motor terminals is due to

    6. A.

     Inadequate motor wiring
    B.

     Poorly regulated power supply
    C.

     Any one of the above
    D.

     None of the above

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  6. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on full load. The machine has 6-poles. The slip of the machine will be

    7. A.

     0.01
    B.

     0.02
    C.

     0.03
    D.

     0.04

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  7. It is advisable to avoid line starting of induction motor and use starter because

    8. A.

     It will run in reverse direction
    B.

     It will pick up very high speed and may go out of step
    C.

     Motor takes five to seven times its full load current
    D.

     Starting torque is very high

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  8. Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor?

    9. A.

     By changing the number of stator poles
    B.

     Rotor rheostat control
    C.

     By operating two motors in cascade
    D.

     By injecting e.m.f. in the rotor circuit

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  9. In three-phase squirrel-cage induction motors

    10. A.

     Rotor conductor ends are short-circuited through slip rings
    B.

     Rotor conductors are short-circuited through end rings
    C.

     Rotor conductors are kept open
    D.

     Rotor conductors are connected to insulation

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  10. In an induction motor if air-gap is increased

    11. A.

     The power factor will be low
    B.

     Windage losses will be more
    C.

     Bearing friction will reduce
    D.

     Copper loss will reduce in an induction motor

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