D.C. Generators Multiple Choice Questions And Answers In English -04

1. With a D.C. generator which of the following regulation is preferred ?
(A) 100% regulation
(B) infinite regulation
(C) 50% regulation
(D) 1% regulation
Ans: D

2. Which generator would you prefer for feeding long D.C. transmission lines ?
(A) Series generator
(B) Shunt generator
(C) Over compound generator
(D) Flat compound generator
Ans: C

3. The main factor which leads to unstable parallel operation of flat and over compounded generators is
(A) their rising voltage characteristics
(B) unequal number of turns in their series field winding’s
(C) unequal speed regulation of their prime movers
(D) unequal series field resistances
Ans: A

4. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to
(A) reverse the field connections
(B) increase the field resistance
(C) increase the speed of prime mover
(D) check armature insulation resistance
Ans: A

5. 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
Ans: C

6. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is
(A) 2
(B) 4
(C) 6
(D) 8
Ans: B

7. For both lap and wave winding’s, there are as many commutator bars as the number of
(A) slots
(B) armature conductors
(C) winding elements
(D) poles
Ans: C

8. The series field of a short-shunt D.C. generator is excited by
(A) external current
(B) armature current
(C) shunt current
(D) load current
Ans: D

9. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately
(A) 40 percent
(B) 25 percent
(C) 10 percent
(D) 5 percent
Ans: D

10. The demagnetising component of armature reaction in a D.C. generator
(A) reduces generator e.m.f.
(B) increases armature speed
(C) reduces interpoles flux density
(D) results in sparking trouble
Ans: A

11. Magnetic field in a D.C. generator is produced by
(A) electromagnets
(B) permanent magnets
(C) both (A) and (B)
(D) none of the above
Ans: A

12. The number of brushes in a commutator depends on
(A) speed of armature
(B) type of winding
(C) voltage
(D) amount of current to be collected
Ans: D

13. Compensating windings are used in D.C. generators
(A) mainly to reduce the eddy currents by providing local short-circuits
(B) to provide path for the circulation of cooling air
(C) to neutralise the cross-magnetising effect of the armature reaction
(D) none of the above
Ans: C

14. In a D.C. generator the actual flux distribution depends upon
(A) size of air gap
(B) shape of the pole shoe
(C) clearance between tips of the adjacent pole shoes
(D) all of the above
Ans: D

15. Shunt generators are most suited for stable parallel operation because of their
(A) rising voltage characteristics
(B) identical voltage characteristics
(C) drooping voltage characteristics
(D) linear voltage characteristics
Ans: C

16. In a shunt generator the voltage build up is generally restricted by
(A) speed limitation
(B) armature heating
(C) insulation restrictions
(D) saturation of iron
Ans: D

17. If a D.C. generator fails to build up the probable cause could not be
(A) imperfect brush contact
(B) field resistance less than the critical resistance
(C) no residual magnetism in the generator
(D) faulty shunt connections tending to reduce the residual magnetism
Ans: B

18. 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
Ans: C

19. In a D.C. machine, short-circuited field coil will result in
(A) odour of burning insulation
(B) unbalanced magnetic pull producing vibrations
(C) reduction of generated voltage for which excitation has to be increased to maintain the voltage
(D) all above
Ans: D

20. Equalizer rings are required in case armature is
(A) wave wound
(B) lap wound
(C) delta wound
(D) duplex wound
Ans: B