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Polyphase Induction Motors - section-1
  1. A pump induction motor is switched on to a supply 30% lower than its rated voltage. The pump runs. What will eventually happen? It will

    2. A.

     Stall after sometime
    B.

     Stall immediately
    C.

     Continue to run at lower speed without damage
    D.

     Get heated and subsequently get damaged

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  2. The circle diagram for an induction motor cannot be used to determine

    3. A.

     Efficiency
    B.

     Power factor
    C.

     Frequency
    D.

     Output

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  3. Short-circuit test on an induction motor cannot be used to determine

    4. A.

     Windage losses
    B.

     Copper losses
    C.

     Transformation ratio
    D.

     Power scale of circle diagram

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  4. The torque of a rotor in an induction motor under running condition is maximum

    5. A.

     At the unit value of slip
    B.

     At the zero value of slip
    C.

     At the value of the slip which makes rotor reactance per phase equal to the resistance per phase
    D.

     At the value of the slip which makes the rotor reactance half of the rotor

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  5. What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero?

    6. A.

     The slip of the motor will be 5%
    B.

     The rotor will not run
    C.

     The rotor will run at very high speed
    D.

     The torque produced will be very large

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  6. In three-phase induction motors sometimes copper bars are placed deep in the rotor to

    7. A.

     Improve starting torque
    B.

     Reduce copper losses
    C.

     Improve efficiency
    D.

     Improve power factor

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  7. The speed characteristics of an induction motor closely resemble the speed-load characteristics of which of the following machines

    8. A.

     D.C. series motor
    B.

     D.C. shunt motor
    C.

     Universal motor
    D.

     None of the above

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  8. Step-less speed control of induction motor is possible by which of the following methods?

    9. A.

     e.m.f. injection in rotor eueuit
    B.

     Changing the number of poles
    C.

     Cascade operation
    D.

     None of the above

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  9. The starting torque of a 3 phase squirrel cage induction motor is

    10. A.

     Twice the full load torque
    B.

     1.5 times the full load torque
    C.

     Equal to full load torque
    D.

     Any of the above

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  10. When the equivalent circuit diagram of double squirrel-cage induction motor is constructed the two cages can be considered

    11. A.

     In series
    B.

     In parallel
    C.

     In series-parallel
    D.

     In parallel with stator

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