DC Generators Multiple Choice Questions And Answers In English -06

1. When two D.C. generators are running in parallel an equalizer bar is used
(A) to increase the series flux
(B) to increase the generated e.m.f.
(C) to reduce the combined effect of AR-mature reaction of both the machines
(D) so that the two identical machines will pass approximately equal currents to the load
Ans: (D)

2. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except
(A) interpoles
(B) dummy coils
(C) compensating winding
(D) shifting of axis of brushes
Ans: (B)

3. Armature coil is short circuited by brushes when it lies
(A) along neutral axis
(B) along field axis
(C) in any of the above positions
(D) in none of the above positions
Ans: (A)

4. A cumulatively compounded long shunt generator when operating as a motor would be
(A) cumulatively compounded long shunt
(B) differentially compounded long shunt
(C) cumulatively compounded short shunt
(D) differentially compounded short shunt
Ans: (B)

5. The rapid wear of brushes takes place due to
(A) abrasion from dust
(B) excessive spring pressure
(C) rough commutator bars
(D) high mica insulation between com-mutation bars
(E) all of the above factors
Ans: (E)

6. Number of tappings for each equilizer ring is equal to
(A) number of pole pairs
(B) number of poles
(C) number of parallel paths
(D) number of commutator segments
Ans: (A)

7. 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
Ans: (D)

8. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(A) just ahead of magnetic neutral axis
(B) in magnetic neutral axis
(C) just behind the magnetic neutral axis

(D) none of the above
Ans: (A)

9. To avoid formation of grooves in the commutator of a D.C. machine
(A) the brushes of opposite polarity should track each other
(B) the brushes of same polarity should track each other
(C) brush position has no effect on the commutator grooving

(D) none of the above
Ans: (A)

10. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
(A) zero
(B) about 2 V
(C) about 50 V
(D) 220 V
Ans: (B)

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
Ans: (A)

12. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?
(A) Series generator
(B) Shunt generator
(C) Compound generator
(D) None of the above
Ans: (D)

13. In over compounded generator, full load terminal voltage is
(A) almost zero
(B) less than no load terminal voltage
(C) more than no load terminal voltage
(D) equal to no-load terminal voltage
Ans: (C)

14. 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
Ans: (D)

15. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will
(A) increase
(B) decrease
(C) remain unaffected
(D) fluctuate heavily
Ans: (B)

16. In a level compounded D.C. generator, full load terminal voltage is
(A) negligibly low
(B) equal to no-load terminal voltage
(C) more than no-load terminal voltage
(D) less than no-load terminal voltage
Ans: (B)

17. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except
(A) armature reaction
(B) armature resistance drop
(C) field weakening due to armature reaction and armature
(D) commutation
Ans: (D)

18. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
(A) zero
(B) small
(C) the same as rated voltage
(D) high
Ans: (A)

19. In case of a flat compounded generator
(A) voltage generated is less than the rated voltage
(B) generated voltage is proportional to the load on the generator
(C) voltage remains constant irrespective of the load
(D) speed varies in proportion to the load on the generator
Ans: (C)

20. Armature reaction in a generator results in
(A) demagnetization of leading pole tip and magnetization of trailing pole tip
(B) demagnetization of trailing pole tip and magnetization of leading pole tip
(C) demagnetizing the center of all poles
(D) magnetizing the center of all poles
Ans: (A)