100+ TOP DCM Lab Viva Questions and Answers

DCM Lab or DC Machines & Synchronous Machines lab Viva Questions :-

1. Why should the field rheostat be kept in the position of minimum resistance?
2. What is the loading arrangement used in a dc motor?
3. How can the direction of rotation of a DC shunt motor be reversed?
4. What are the mechanical and electrical characteristics of a DC shunt motor?
5. What are the applications of a DC shunt motor?
6. What is meant by armature reaction?
7. How should a generator be started?
8. How should a Shunt or compound generator be started?
9. When a generator loses its residual flux due to short circuit, how can it be made to build up?
10. What causes heating of armature?
11. What will happen if both the currents are reversed?
12. What will happen if the field of a d.c shunt motor is opened?
13. What happens if the direction of current at the terminals of series motor is reversed?
14. Explain what happens when a d.c motor is connected across an a.c supply?
15. Why does a d.c motor sometimes spark on light load?
16. A d.c motor fails to start when switched on. What could be the possible reasons and remedies?
17. What is meant by back e.m.f?
18. Discuss different methods of speed control of a d.c motor.
19. Why a d.c series motor should not be started at No load?
20. What are the losses that occur in d.c machines?
21. State some present day uses of d.c machines.
22. Write down the equation for frequency of emf induced in an Alternator.
23. Name the types of Alternator based on their rotor construction.
24. Which type of Synchronous generators are used in Hydro-electric plants and why?
25. What are the advantages of salient pole type construction used for Synchronous machines?
26. Why is the stator core of Alternator laminated?
27. What are the causes of changes in voltage in Alternators when loaded?
28. Define the term voltage regulation
29. State the condition to be satisfied before connecting two alternators in parallel
30. What is meant by infinite bus-bars?
31. How do the synchronizing lamps indicate the correctness of phase sequence between existing and incoming Alternators?
32. Why are Alternators rated in kVA and not in kW?
33. Why a DC series motor should never be stared without load?
34. Why a DC series motor has a high starting torque?
35. Compare the resistances of the field windings of DC shunt and series motor?
36. What are the applications of DC series motor?
37. Comment on the Speed – Torque characteristics of a DC series motor.
38. How does the torque vary with the armature current in a DC series motor?
39. How does the speed of a DC shunt motor vary with armature voltage and field current?
40. Compare the resistance of the armature and field winding.
41. What is the importance of speed control of DC motor in industrial applications?
42. Which is of the two methods of speed control is better and why?
43. Why is the speed of DC shunt motor practically constant under normal load condition?
44. What are the factors affecting the speed of a DC shunt motor?
45. What is meant by residual magnetism?
46. What is critical field resistance?
47. What is meant by saturation?
48. What is the difference between external and internal characteristics?
49. What is the purpose of Swinburne’s test?
50. What are the constant losses in a DC machine?
51. What are the assumptions made in Swinburne’s test?
52. Why is the indirect method preferred to the direct loading test?
53. The efficiency of DC machine is generally higher when it works as a generator than motor. Is this statement true or false? Justify your answer with proper reasons
54. What is the purpose of Hopkinson’s test?
55. What are the precautions to be observed in this test?
56. What are the advantages of Hopkinson’s test?
57. What are the conditions for conducting the test?
58. Why the adjustments are done in the field rheostat of generator and motor?
59. If the voltmeter across the SPST switch reads zero what does it indicate? If it does not read zero value what does it indicate?
60. What are the other names for Hopkinson’s test?
61. Why is armature resistance less than field resistance of dc shunt machine?
62. Why is armature resistance more than field resistance of dc series machine?
63. Write the emf equation of DC and AC machine. 64. Write the torque equation of DC motor.
65. Which is the most common type of fault occurring in a power system?
66. What are unsymmetrical faults?

DCM Lab Viva Questions ::