Dc Generator mcq - dc generator electrical engineering Multiple Choice Questions - Electrical input

Sunday, August 5, 2018

Dc Generator mcq - dc generator electrical engineering Multiple Choice Questions

                                                      Dc Generator mcq

dc generator Multiple Choice Questions:-

1.        The armature of D.C. generator is laminated to
 (a) insulate the core
 (b) provide the bulk
 (c) reduce the bulk
 (d) reduce eddy current loss
Ans:- d

 The field coils of D.C. generator are usually made of
 (a) copper
 (b) carbon
 (c) cast iron
 (d) mica
  Ans:- a

             In  commutator--
(a)    mica and copper are equally  hard
(b)   copper is harder than mica
(c)    mica is harder than copper
(d)   none of the above
ans ----c

4.       dc  generators of the pole shoes are fastened to the pole core by---
(a)    Counter sunk screws
(b)   Rivets
(c)    Welding
(d)   Brazing
Ans :- a

        5.   Fleming’s right-hand rule regarding direction of induced e.m.f., correlates
             (a) magnetic flux, direction of current flow and resultant force
             (b) magnetic flux, direction of force and direction of motion of conductor
             (c) magnetic field strength, induced voltage and current
             (d) magnetic flux, direction of motion and the direction of e.m.f. induced
              Ans:- d

         6. In the lap winding, the number of brushes is always---
              (a) half the number of poles
              (b) same as the number of poles
              (c) double the number of poles
             Ans:- b

            7.  in dc  generators, cause of rapid brush wear may be----
                (a) imperfect contact
                (b) rough commutator surface
                 (c)  severe sparking
                (d) any of the above
                  Ans:- d

           8. In case of D.C. machines, mechanical losses are primary function of---
               (a). current
               (b) . voltage
               (c) . speed
               (d) . none of above
                Ans:- c

9.--brushes of a dc  generator moved  to bring these brushes in magnetic neutral axis, there will be---
(a). demagnetisation only
(b). cross magnetisation as well as mag-metisation
©, crossmagnetisation as well as demagnetising
(d). cross magnetisation only
Ans:- c

10. Armature reaction of an unsaturated D.C. machine is--
(a). cross magnetising
(b). demagnetising
©. magnetising
(d). none of above
Ans:- a

11. Eddy currents are induced in the pole shoes of a D.C. machine due to--
(a). oscillating magnetic field
(b). pulsating magnetic flux
©. relative rotation between field and armature
(d). all above
Ans: c

 12. . Equilizer rings are required in case armature is---
(a) duplex wound
(b) lap wound
(c) delta wound
(d) wave wound
Ans:- b

13. In case of D.C. machine winding, number of commutator segments is equal to---
(a) number of armature turns
(b) number of armature conductors
(c)number of armature coil sides
(d) number of armature coils

Ans:- d

14. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the mag-’netic path
(b) to spread out the flux to achieve uniform flux density
(c) to support the field coil
(d) to discharge all the above functions
Ans:- a

15. Magnetic field in a D.C. generator is produced by---
(a) permanent magnets
(b) electromagnets
(c) both (a) and (b)
(d) none of the above
Ans:-- b

16. in a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(a) using carbon brushes of superior quality
(b) using commutator with large number of segments
(c) using conductor of annealed copper
(d) using equiliser rings
Ans:- a

17. Shunt generators are most suited for stable parallel operation because of their---
(a) linear voltage characteristics
(b) identical voltage characteristics
(c) rising voltage characteristics
(d) drooping voltage characteristics
Ans:- d

18. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately-----
(a) 5 %
(b) 10 %
(c) 25 %
(d) 40 %
Ans:- a

19. The series field of a short-shunt D.C. generator is excited by
(a) shunt current
(b) armature current
(c) load current
(d)  external current
Ans:- c

20. in a D.C. generator the critical resistance can be increased by
(a) increasing its field resistance
(b) increasing its speed
(c) decreasing its field resistance
(d) decreasing its speed
Ans:-  b

21. Which generator would you prefer for feeding long D.C. transmission lines---
(a) Over compound generator
(b)  Flat compound generator
(c) Shunt generator
(d) Series generator
Ans:- a

22. When two D.C. generators are running in parallel an equilizer bar is used
(a) to increase the generated e.m.f
(b) so that the two identical machines will pass approximately equal currents to the load
(c) to reduce the combined effect of ar-mature reaction of both the machines
(d) to increase the senes flux
Ans:- b

23. The essential condition for parallel operation of two D.C. generators is that they have
(a) the same drooping voltage characteristics
(b) the same operation r.p.m
(c) same kW rating
(d) same percentage regulation

24. A shunt generator can self-excite---
(a) only if the resistance of the field circuit is greater than critical value
(b)  only if the resistance of the field circuit is less than critical value
(c) irrespective of the value of the resistance in the field circuit
(d) None of the above
Ans:- b

25. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons----
(a) The speed of that generator is increased
(b) The direction of that generator is reversed
(c) That generator takes large share of loads
(d)  The field of that generator is weakened

26. Wave winding is composed of
(a) that even number which is exact multiple of poles
(b) that even number which is exact multiple of poles + 2
(c) any odd number of conductors
(d)  any even number of conductors
Ans:-- b

27. When two D.C. series generators are running in parallel, an equilizer bar is used

(a) to reduce the combined effect of armature reaction of both machines
(b) so that two similar machines will pass approximately equal currents to the load
(c) to increase the speed and hence generated e.m.f
(d) to increase the series flux
    Ans:- b

28. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
(a) Shunt field
(b Inter pole field
(c) Compensating field
(d) Series field
Ans:-- write in comment box

29. In a D.C. generator ----
(a) mag netisation characteristic = external characteristic
(b) external characteristic = magnetisation characteristic - ohmic drop - armature reaction
(c) external resistance = internal char-actenstic - armature reaction
(d) internal characteristic = magnetisation characteristic - ohmic drop
Ans:- b

30. Which of the following generator will have negligible terminal voltage while running on no-load ---
(a) Separately excited generator
(b) Shunt generator
(c) Compound generator
(d) Series generator
Ans:-- a

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