DC Machines

31 Questions | Total Attempts: 816

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Fundamentals Quizzes & Trivia

This is a short quiz on DC machines fundamentals


Questions and Answers
  • 1. 
    Winding used for low voltage high current
    • A. 

      Lap winding

    • B. 

      Wave Winding

    • C. 

      Gram ring winding

    • D. 

      Open winding

  • 2. 
    No. of parallel paths in lap winding=_________
    • A. 

      Number of poles

    • B. 

      2

    • C. 

      4

    • D. 

      6

  • 3. 
    In long shunt compound generator Ise = ____________
    • A. 

      Ia-Ish

    • B. 

      IL

    • C. 

      Ia

    • D. 

      Ia+Ish

  • 4. 
    Generated emf is __________ speed of prime mover
    • A. 

      Directly proportional to

    • B. 

      Inversely proportional to

    • C. 

      Equal to

    • D. 

      Less than

  • 5. 
    For a 4 pole lap wound DC generator with 32 armature slots, average pitch is
    • A. 

      2

    • B. 

      4

    • C. 

      8

    • D. 

      16

  • 6. 
    ________ compound generator is used for arc welding
    • A. 

      Long shunt

    • B. 

      Short shunt

    • C. 

      Differential

    • D. 

      Commulative

  • 7. 
    % efficiency = ___________
    • A. 

      (Po/Pi)x100

    • B. 

      (Po/Po+Losses)x100

    • C. 

      Both a & b

    • D. 

      None of above

  • 8. 
    If VN > VL , Voltage regulation is _________
    • A. 

      Negative

    • B. 

      Positive

    • C. 

      Zero

    • D. 

      1

  • 9. 
    Power P (in watts) = __________
    • A. 

      BHPx746

    • B. 

      BHP/746

    • C. 

      BHPx764

    • D. 

      BHP/764

  • 10. 
    Series generators are used for
    • A. 

      Series arc lighting

    • B. 

      Voltage booster

    • C. 

      Regenerative breaking

    • D. 

      All of above

  • 11. 
    A 110V, 1000 rpm generator will generate ____ V at 1100 rpm
    • A. 

      220

    • B. 

      200

    • C. 

      150

    • D. 

      120

  • 12. 
    Cu-Losses are also known as
    • A. 

      I2R

    • B. 

      IR2

    • C. 

      V2/R

    • D. 

      VI

  • 13. 
    _________ field winding has small number of turns of thick copper wire.
    • A. 

      Shunt

    • B. 

      Series

    • C. 

      Compund

    • D. 

      Separately excited

  • 14. 
    Carbon brushes are preferred on copper brushes because of
    • A. 

      Armature reaction

    • B. 

      Reduced reactance voltage

    • C. 

      Hardness of material

    • D. 

      Low resistance

  • 15. 
    In Fleming's right-hand rule, the thumb point towards
    • A. 

      Direction of flux

    • B. 

      Direction of induced e.m.f.

    • C. 

      Direction of motion of conductor

    • D. 

      Any of above

  • 16. 
    The output voltage of a simple d.c. generator is
    • A. 

      A.c. square wave.

    • B. 

      A.c. sinusoidal wave

    • C. 

      Pure d.c

    • D. 

      Pulsating d.c

  • 17. 
    When tow generators are running in parallel and field of one of them is weakened too much then it will
    • A. 

      Deliver large share of the total load

    • B. 

      Deliver small share of the total load

    • C. 

      Run in the opposite direction

    • D. 

      Run as a motor in the same direction

  • 18. 
    In shunt generator interpole winding carries ____ current
    • A. 

      Armature

    • B. 

      Shunt field

    • C. 

      Full load

    • D. 

      None of these

  • 19. 
    Due to which of the following reasons a separately excited generator is better
    • A. 

      Low price

    • B. 

      Exciting current is independent of load current

    • C. 

      Low armature resistance

    • D. 

      All of above

  • 20. 
    Why is the armature of a d.c. machine made of silicon steel
    • A. 

      To reduce eddy current loss

    • B. 

      To reduce hysteresis loss

    • C. 

      Ease of creating slots

    • D. 

      To achieve high permeability

  • 21. 
    compound generator is said to be flat compounded if VFL
    • A. 

      > VNL

    • B. 

      < VNL

    • C. 

      = VNL

    • D. 

      = 2VNL

  • 22. 
    The commutator segments of a d.c. machine are made of
    • A. 

      Carbon

    • B. 

      Copper

    • C. 

      Mica

    • D. 

      Ceramic

  • 23. 
    If the number of poles in a lap wound generator be doubled, then the generated e.m.f .will
    • A. 

      Become half

    • B. 

      Become double

    • C. 

      Increase to four times

    • D. 

      Remain constant

  • 24. 
    Which of the following d.c. generator can build up without any residual magnetism
    • A. 

      Compound generator

    • B. 

      Self-excited generator

    • C. 

      Series generator

    • D. 

      Shunt generator

  • 25. 
    The efficiency of a d.c. machine is maxiinum when
    • A. 

      Variable losses = constant losses

    • B. 

      Stray losses are = copper losses

    • C. 

      Field copper losses = armature copper losses

    • D. 

      Magnetic losses - windage loss.

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