DC Generator

76 Questions | Total Attempts: 198

SettingsSettingsSettings
Please wait...
DC Generator

.


Questions and Answers
  • 1. 
    In D.C. generators, the cause of rapid brush wear may be
    • A. 

       Severe sparking

    • B. 

       Rough commutator surface

    • C. 

      Imperfect contact

    • D. 

      Any of the above

  • 2. 
    The insulating material used between the commutator segments is normally
    • A. 

      Graphite

    • B. 

      Paper

    • C. 

      Mica

    • D. 

      Insulating varnish

  • 3. 
    Eddy currents are induced in the pole shoes of a D.C. machine due to  
    • A. 

      Oscillating magnetic field

    • B. 

      Pulsating magnetic flux

    • C. 

      Relative rotation between field and armature

    • D. 

      All above

  • 4. 
    Which of the following statement about D.C. generators is false?
    • A. 

      Compensating winding in a D.C. machine helps in commutation

    • B. 

       In a D. C. generator interpoles winding is connected in series with the armature winding

    • C. 

      Back pitch and front pitch are both odd and approximately equal to the pole pitch

    • D. 

      Equalizing bus bars are used with parallel running of D.C. shunt generators

  • 5. 
     In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
    • A. 

      Using conductor of annealed copper

    • B. 

       Using commutator with large number of segments

    • C. 

      Using carbon brushes of superior quality

    • D. 

      Using equalizer rings

  • 6. 
    Satisfactory commutation of D.C. machines requires  
    • A. 

      Brushes should be of proper grade and size

    • B. 

      Brushes should smoothly run in the holders

    • C. 

      Smooth, concentric commutator properly undercut

    • D. 

      All of the above

  • 7. 
    In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when    
    • A. 

      R.p.m. is more than 300

    • B. 

      r.p.m. is less than 300

    • C. 

      Number of poles is 4

    • D. 

      Number of poles is 2

  • 8. 
     The following constitute short-circuit in the armature winding.  
    • A. 

      Insulation failure between two commutator bars

    • B. 

      Insulation failure between two turns of a coil

    • C. 

      Two of more turns of the same coil getting grounded

    • D. 

      All of the above

  • 9. 
     In a D.C. machine stray loss is the sum of
    • A. 

      Total copper loss and mechanical loss

    • B. 

      Armature copper loss and iron loss

    • C. 

      Shunt field copper loss and mechanical loss

    • D. 

       Iron loss and mechanical loss

  • 10. 
     Which of the following generator will have negligible terminal voltage while running on no-load?
    • A. 

       Series generator

    • B. 

       Shunt generator

    • C. 

      Compound generator

    • D. 

      Separately excited generator

  • 11. 
     In a separately excited generator supplying rated load the armature reaction:
    • A. 

       Is always present

    • B. 

      Is always absent

    • C. 

       May be sometimes present

    • D. 

      None of the above

  • 12. 
    . When two D.C. series generators are running in parallel, an equalizer bar is used
    • A. 

      To increase the speed and hence generated e.m.f.

    • B. 

      To increase the series flux

    • C. 

      So that two similar machines will pass approximately equal currents to the load

    • D. 

      Efect of armature reaction To reduce the combined of both machines

  • 13. 
     A D.C. generator works on the principle of
    • A. 

      Lenz's law

    • B. 

      Ohm's law

    • C. 

       Faraday's law of electromagnetic induction

    • D. 

      None of the above

  • 14. 
    Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be    
    • A. 

      270 V

    • B. 

      267.5 V

    • C. 

      265 V

    • D. 

      257.4 V

  • 15. 
    In a D.C. generator the critical resistance can be increased by
    • A. 

      Increasing its field resistance

    • B. 

      Decreasing its field resistance

    • C. 

      Increasing its speed

    • D. 

      Decreasing its speed

  • 16. 
    For both lap and wave windings, there are as many commutator bars as the number of
    • A. 

      Slots

    • B. 

       Armature conductors

    • C. 

       Winding elements

    • D. 

      Poles

  • 17. 
     In case of D.C. machine winding, number of commutator segments is equal to
    • A. 

      Number of armature coils

    • B. 

      Number of armature coil sides

    • C. 

      Number of armature conductors

    • D. 

      Number of armature turns

  • 18. 
    A  D.C. welding generator has
    • A. 

      Lap winding

    • B. 

      Wave moving

    • C. 

      Duplex winding

    • D. 

       Any of the above

  • 19. 
     DC shunt generator has terminal voltage versus load current characteristic which is
    • A. 

      Constant

    • B. 

      Slightly drooping

    • C. 

      Slightly rising

    • D. 

      Highly drooping

  • 20. 
    The material for commutator brushes is generally
    • A. 

      mica 

    • B. 

      Copper

    • C. 

      Cast iron 

    • D. 

      carbon

  • 21. 
    The insulating material used between the commutator segments is normally
    • A. 

      graphite 

    • B. 

      Paper

    • C. 

      Mica

    • D. 

      insulating varnish

  • 22. 
    3.In D.C. generators, the brushes on commutator remain in contact with conductors which
    • A. 

      lie under south pole

    • B. 

      Lie under north pole

    • C. 

      Lie under interpolar region

    • D. 

      are farthest from the poles

  • 23. 
    4.If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
    • A. 

      demagnetisation only

    • B. 

      Cross magnetisation as well as mag¬netisation

    • C. 

      Crossmagnetisation as well as demagnetising

    • D. 

      cross magnetisation only

  • 24. 
    Armature reaction of an unsaturated D.C. machine is
    • A. 

      crossmagnetising

    • B. 

      Demagnetising

    • C. 

      Magnetising 

    • D. 

      none of above

  • 25. 
    D.C. generators are connected to the busbars or disconnected from them only under the floating condition
    • A. 

      to avoid sudden loading of the primemover

    • B. 

      To avoid mechanicaljerk to the shaft

    • C. 

      To avoid burning of switch contacts

    • D. 

      all above

Back to Top Back to top