Electrical Machine Design MCQ Electrical Engineering

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About Electrical Machine Design

Following are some of the multiple choice questions on the Electrical Machine Design with answers that will help the students in developing their knowledge.

Electrical Machine Design MCQ

1. In D.C. machines the number of slots per pole usually lies

  • between 2 to 4
  • between 6 to 8
  • between 9 to 16
  • between 20 to 30

2. In D.C. machines the usual limit of slot pitch is

  • between 5 to 10 mm
  • between 10 to 15 mm
  • between 15 to 20 mm
  • between 25 to 35 mm

3. Which of the following methods may be adopted to reduce the effects of armaturereaction ?

  • Increase in length of air gap at pole tips
  • Increasing reluctance of pole tips
  • Compensating windings
  • All of the above

4. The operation of a D.C. machine with large air gap lengths is comparatively

  • quiet
  • noisy
  • either of the above
  • none of the above

5. In D.C. machines, the ____ in field mmf results in increase in size and cost of machines.

  • increase
  • decrease
  • either of the above
  • none of the above

6. In D.C. machines, ir order to prevent excessive distortion of field form by the armaturereaction, the field mmf must be made

  • equal to that of armature mmf
  • less in comparison with the arma¬ture mmf
  • large in comparison with the arma-ture mmf
  • none of the above

7. D.C. machines designed with a large value of air gap length have

  • worst, ventilation
  • poor ventilation
  • better ventilation
  • none of the above

8. In D.C. machines the width of the duct is usually

  • 4 mm
  • 6 mm
  • 8 mm
  • 10 mm

9. In a D.C. machine, the value of peripheral speed should not, normally, exceed

  • 10 m/s
  • 20 m/s
  • 30 m/s
  • 40 m/s

10. In a D.C. machine the current per brush arm should not be more than

  • 100 A
  • 200 A
  • 300 A
  • 400 A

11. In a D.C. machine the number of brush arms is _____ the number of poles.

  • less than
  • equal to
  • greater than
  • none of the above

12. The weight of copper of both armature and field windings decreases with _____ innumber of poles.

  • increase
  • decrease
  • either of the above
  • none of the above

13. Which of the following problem arises in D.C. motors which are fed from thyristorbridge circuits ?

  • Increased I R losses
  • Increased core losses
  • Poor commutation
  • All of the above

14. ________ is the common method of applying brushes to the commntator.

  • Radial
  • Trailing
  • Reaction
  • All of the above

15. Which of the following brushes can be used for high values of current density ?

  • Metal graphite brushes
  • Hard carbon brushes
  • Electro-graphitic brushes
  • Natural graphite brushes

16. ______ brushes are fragile and cause excessive wear of commutator,

  • Natural graphite
  • Hard carbon
  • Electro graphitic
  • Metal graphite

17. Is usually used for brush rockers

  • Mild steel
  • Copper
  • Aluminium
  • Cast-iron

18. The laminations of the armature of a D.C. machine are usually _____ thick.

  • 0.1 to 0.2 mm
  • 0.2 to 0.3 mm
  • 0.3 to 0.4 mm
  • 0.4 to 0.5 mm

19. A practical formula for determining the thickness of insulation between low voltageand high voltage windings is

  • 1 + 0.2 kVmm
  • 2 + 0.5 kVmm
  • 4 + 0.7 kV mm
  • 5 + 0.9 kV mm

20. Dummy coil should not be used in

  • small machines
  • large machines
  • either (a) or (b)
  • none of the above

21. Power transformers have rating

  • equal to 50 kVA
  • equal to 100 kVA
  • above 200 kVA
  • none of the above

22. Power transformers should be designed to have maximum efficiency

  • at one-fourth load
  • at one-half load
  • at or near full load
  • any of the above

23. In transformers using hot rolled steel, the cross-section of the yoke is made about _____ greater than that of the core

  • 5 percent
  • 10 percent
  • 15 percent
  • 30 percent

24. Yokes with rectangular cross-section are used for

  • small capacity transformers
  • medium capacity transformers
  • large capacity transformers
  • any of the above

25. The cold rolled grain oriented steel has ______ permeability in the direction of thegrain orientation.

  • minimum
  • maximum
  • nil
  • none of the above

26. Cylindrical windings using circular conductors, employed in transformers, are

  • single layered
  • double layered
  • multi-layered
  • none of the above

27. Helical windings are used in

  • distribution transformers
  • power transformers
  • shell type transformers
  • none of the above

28. Multi-layer helical windings are commonly used in the transformers as high voltagewindings

  • upto 20 kV
  • upto 50 kV
  • upto 80 kV
  • for 110 kV and above

29. Disc windings are primarily used in

  • short capacity transformers
  • medium capacity transformers
  • high capacity transformers
  • any of the above

30. The heat dissipating capability of transformers of ratings higher than 30 kVA inincreased by providing which of the following ?

  • Corrugations
  • Fins
  • Tubes
  • All of the above

31. Transformers with a capacity of upto _____ have a cooling radiator system with naturalcooling

  • 2 MVA
  • 5 MVA
  • 7.5 MVA
  • 10 MVA

32. The forced oil and air circulation method is usual one for transformers of capacities

  • upto 5 MVA
  • upto 10 MVA
  • upto 20 MVA
  • 30 MVA upwards

33. The flash point of transformer oil should be higher than

  • 40°C
  • 60°C
  • 80°C
  • 104°C

34. D.C. windings are

  • sometimes 2-layer type
  • never 2-layer type
  • always 2-layer type
  • none of the above

35. The stator of a D.C. machine comprises of

  • main poles
  • interpoles
  • frame
  • all of the above

36. D.C. servomotors are used in

  • purely control systems
  • purely A control systems
  • both and A control systems
  • none of the above

37. Which of the following in an application of D.C. motors?

  • Traction
  • Drives for process industry
  • Battery driven vehicles
  • All of the above

38. The surge phenomenon is particularly important in case of

  • low voltage transformers
  • medium voltage transformers
  • high voltage transformers
  • any of the above

39. The cylindrical windings using circular conductors are used for current rating of

  • upto 20 A
  • upto 40 A
  • upto 60 A
  • upto 80 A

40. The insulation between windings and grounded core and the insulation between thewindings of the same phase is called

  • minor insulation
  • major insulation
  • either of the above
  • none of the above

41. Which of the following is the basic consideration in the design of insulation ?

  • Electrical considerations
  • Mechanical considerations
  • Thermal considerations
  • All of the above

42. The high voltage winding is usually which of the following type ?

  • Cylindrical winding with circular conductors
  • Cross-over winding with either circular or small rectangular conductors
  • Continuous disc type winding with rectangular conductors
  • All of the above types

43. A current density of _____ is ilsed for large power transformers with forced circulationof oil or with water cooling coils

  • 1.5 to 2.5 A/mm2
  • 3.5 to 4.5 A/mm2
  • 4.0 to 5.0 A/mm2
  • 5.4 to 6.2 A/mm2

44. For large power transformers, self oil cooled type or air blast type which of thefollowing values of current density may be used ?

  • 1.0 to 1.2 A/mm2
  • 1.5 to 2.0 A/mm2
  • 2.2 to 3.2 A/mm2
  • 3.2 to 4.2 A/mm2

45. For 275 kV transformers, using cold rolled grain oriented steel, which of the followingvalues of flux density may be used?

  • 1.0 Wb/m2
  • 1.1 Wb/m2
  • 1.3 Wb/m2
  • 1.6 Wb/m2

46. The usual values of maximum flux densities for distribution transformers using hotrolled silicon steel are

  • 0.5 to 0.8 Wb/m2
  • 0.8 to 1.0 Wb/m2
  • 1.1 to 1.35 Wb/m2
  • 1.4 to 1.8 Wb/m2

47. The voltage control in electric supply networks in required on account of which of the following reasons ?

  • Adjustment of voltage at consumers premises within statutory limits
  • Control of active and reactive power
  • Adjustment of short period daily and seasonal voltage variations in accordance with variations of load
  • All of the above

48. Are always double layer type.

  • Closed windings
  • Open windings
  • Either of the above
  • None of the above

49. The distance between the starts of two consecutive coils measured in terms of coilsides is called

  • front pitch
  • winding pitch
  • commutator pitch
  • back pitch

50. The winding where dummy coils are used is sometimes called

  • duplex winding
  • triplex winding
  • forced winding
  • none of the above

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