The Electrician Workbook Electrical Machines

47 Questions | Total Attempts: 620

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Electrical Quizzes & Trivia

For those of you who love all things physics and mathematics especially electrical machines then this is the quiz for you. If you are prepared to test your knowledge and yearn to get more understanding on it, try it out.


Questions and Answers
  • 1. 
    The basic function of a transformer is to change
    • A. 

      The level of the voltage.

    • B. 

      The power level.

    • C. 

      The power factor.

    • D. 

      The frequency.

  • 2. 
    Transformer is used
    • A. 

      To step up the voltage.

    • B. 

      To step down the voltage.

    • C. 

      On dc.

    • D. 

      To step up or step down the voltage.

  • 3. 
    An infinite bus-bar has
    • A. 

      Constant voltage.

    • B. 

      Constant frequency.

    • C. 

      Infinite voltage.

    • D. 

      Both A and B.

    • E. 

      Both B and C.

  • 4. 
    The emfs generated in three phases of an alternator are _______ electrical degrees apart.
    • A. 

      60

    • B. 

      90

    • C. 

      120

    • D. 

      180

  • 5. 
    Tappings of a transformer are provided
    • A. 

      At the phase end of LV side.

    • B. 

      At the phase end of HV side.

    • C. 

      At the neutral end of HV side.

    • D. 

      At the middle of HV side.

  • 6. 
    The auto-transformer is preferably employed in situations where voltage transformation ratio is
    • A. 

      Very low.

    • B. 

      Near unity.

    • C. 

      Very high.

    • D. 

      Unity.

  • 7. 
    An auto-transformer may be used as a/an ___________ transformer.
    • A. 

      Power

    • B. 

      Distribution

    • C. 

      Automatically operated

    • D. 

      Voltage regulating

    • E. 

      Instrument

  • 8. 
    An auto-transformer has
    • A. 

      One winding with taps taken out.

    • B. 

      Two interlaced windings.

    • C. 

      Two windings of same wire.

    • D. 

      Two windings of different materials.

    • E. 

      One winding without taps.

  • 9. 
    The principle of operation of a 3-phase induction motor closely resembles to that of a
    • A. 

      Two winding transformer with its secondary short-circuited.

    • B. 

      Two winding transformer with its secondary open-circuited.

    • C. 

      Synchronous motor.

    • D. 

      Dc shunt motor.

  • 10. 
    The relative speed between stator and rotor fluxes is equal to
    • A. 

      Synchronous speed, Ns.

    • B. 

      Rotor speed, N.

    • C. 

      Zero

    • D. 

      Ns-N

  • 11. 
    An induction motor works with
    • A. 

      DC only.

    • B. 

      AC only.

    • C. 

      AC and DC both.

    • D. 

      None of these.

  • 12. 
    The two important parts of an induction motor are
    • A. 

      Stator and rotor.

    • B. 

      Slip rings and brushes.

    • C. 

      Core and winding.

    • D. 

      Shaft and ball bearings.

  • 13. 
    When two alternators are operating in parallel, if the power input to one of the alternators is cut-off, the alternator will
    • A. 

      Continue to run as a synchronous motor rotating in the same direction.

    • B. 

      Continue to run as a synchronous motor rotating in opposite direction.

    • C. 

      Stop running.

    • D. 

      Get damaged due to burning of stator and rotor windings.

  • 14. 
    A 3-phase synchronous motor will not start if
    • A. 

      Voltage is too low.

    • B. 

      One phase is open.

    • C. 

      Connections are faulty.

    • D. 

      Any of the above.

  • 15. 
    Synchronous motors are inherently not self-starting motors as
    • A. 

      The direction of instantaneous torque on the rotor reverses after each half cycle.

    • B. 

      There is no slip.

    • C. 

      The stator does not produce revolving magnetic field.

    • D. 

      It has no starting winding.

  • 16. 
    Which of the following electric motors is not inherently self starting motor?
    • A. 

      Synchronous motor.

    • B. 

      3-phase induction motor.

    • C. 

      Reluctance motor.

    • D. 

      DC series motor.

  • 17. 
    In a synchronous motor, squirrel cage winding is provided for making motor
    • A. 

      Noise free.

    • B. 

      Self starting.

    • C. 

      Cheap.

    • D. 

      Quick start.

  • 18. 
    The method that can be used conveniently for speed control of a squirrel cage induction motor is
    • A. 

      Pole changing control.

    • B. 

      Rotor resistance control.

    • C. 

      Cascade operation.

    • D. 

      Secondary foreign voltage control.

  • 19. 
    Synchronous speed of an induction motor can be increased by
    • A. 

      Reducing mechanical friction.

    • B. 

      Increasing supply voltage.

    • C. 

      Increasing number of poles.

    • D. 

      Increasing supply frequency.

  • 20. 
    If the prime-mover of an alternator supplying load to an infinite bus is suddenly shut down, then it will
    • A. 

      Stop.

    • B. 

      Continue to run as an alternator.

    • C. 

      Continue to run as a synchronous motor in the reverse direction.

    • D. 

      Continue to run as a synchronous motor in the same direction.

  • 21. 
    While starting a synchronous motor its field winding should be
    • A. 

      Kept open.

    • B. 

      Short-circuited.

    • C. 

      Connected to a DC source.

    • D. 

      None of the above.

  • 22. 
    Synchronous capacitor is
    • A. 

      An ordinary static capacitor bank.

    • B. 

      An over-excited synchronous motor driving mechanical load.

    • C. 

      An over-excited synchronous motor without mechanical load.

    • D. 

      None of the above.

  • 23. 
    When the induction motor is in standstill, the slip is
    • A. 

      Zero.

    • B. 

      1.

    • C. 

      Infinity.

    • D. 

      None of the above.

  • 24. 
    An electric motor gets over-heated. This may be due to
    • A. 

      Over-loading.

    • B. 

      Shorted stator winding.

    • C. 

      Worn-out or dry bearings.

    • D. 

      Low or high voltage.

    • E. 

      Any of the above.

  • 25. 
    A squirrel cage induction motor is not favoured when _______________ is the main consideration.
    • A. 

      Initial cost.

    • B. 

      Maintenance cost.

    • C. 

      High starting torque.

    • D. 

      Higher efficiency and higher power factor.

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