electrical machine design MCQs – Page 3

Practise focused electrical machine design questions with marked answers for exam preparation and subject revision.

electrical machine design Mcqs
41. On which of the following variables heat convected depends ?
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A. Gravitational constant

B. Thermal resistivity, density, specific heat

C. All of the above

D. Temperature difference between heated surface and coolant

E. Power density

42. The noise produced by a ___________ cooled machine is less as the rotor moves in a medium of smaller density?
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A. hydrogen

B. air

C. none of the above

D. either A. or B.

43. The flash point of transformer oil should be higher than_______________?
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A. 104C

B. 60C

C. 80C

D. 40C

44. Materials exhibiting zero value of resistivity are known as ____________ ?
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A. conductors

B. superconductors

C. insulators

D. semiconductors

45. The distance between the starts of two consecutive coils measured in terms of coil sides is called_____________?
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A. winding pitch

B. back pitch

C. commutator pitch

D. front pitch

46. For 275 kV transformers, using cold rolled grain oriented steel, which of the following values of flux density may be used?
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A. 1.6 Wb/m2

B. None of the above

C. 1.0 Wb/m2

D. 1.1 Wb/m2

E. 1.3 Wb/m2

47. The slot leakage can be calculated by making which of the following assumptions ?
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A. All of the above

B. The leakage path is straight across the slot and around the iron at the bottom

C. The permanence of air paths is only considered. The reluctance of iron paths is assumed as zero

D. The current in the slot conductors is uniformly distributed over their cross-section

48. The heat dissipating capability of transformers of ratings higher than 30 kVA in increased by providing which of the following ?
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A. Corrugations

B. Fins

C. All of the above

D. Tubes

E. Radiator tanks

49. Which of the following methods is used for air cooling of turbo-alternators ?
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A. All of the above

B. One sided axial ventilation

C. Two sided axial ventilation

D. Multiple inlet system

50. Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?
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A. Increased I R losses

B. Increased core losses

C. Poor commutation

D. All of the above

E. Change in motor parameters

51. The heat dissipated by from a surface depends upon its temperature and its characteristics like colour, roughness etc?
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A. convection

B. conduction

C. radiation

D. any of the above

52. In D.C. machines the number of slots per pole usually lies___________?
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A. between 2 to 4

B. between 9 to 16

C. between 6 to 8

D. between 20 to 30

53. With conventional hydrogen cooling it is possible to increase the rating of a single unit to___________?
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A. 200 MW

B. 50 MW

C. 100 MW

D. none of the above

54. Which of the following methods does not take into account the maximum temperature rise under variable load conditions ?
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A. Equivalent power method

B. Method of average losses

C. Equivalent torque method

D. Equivalent current method

55. Helical windings are used in________________?
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A. shell type transformers

B. none of the above

C. power transformers

D. distribution transformers

56. The high voltage winding is usually which of the following type ?
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A. Continuous disc type winding with rectangular conductors

B. Cross-over winding with either circular or small rectangular conductors

C. Cylindrical winding with circular conductors

D. All of the above types
57. The weight of copper of both armature and field windings decreases with __________ in number of poles?
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A. none of the above

B. decrease

C. either of the above

D. increase
58. The winding where dummy coils are used is sometimes called______________?
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A. triplex winding

B. none of the above

C. duplex winding

D. forced winding
59. The time taken by the machine to attain 0.632 of its final steady temperature rise is called_____________?
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A. cooling time constant

B. heating time constant

C. none of the above

D. either A. or B.

60. The cold rolled grain oriented steel has _________ permeability in the direction of the grain orientation?
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A. maximum

B. minimum

C. none of the above

D. nil