Thursday, September 10, 2020

Chapter 6 : DC Machines-Page 6

Chapter 6 : DC Machines

51. Core losses in a dc machine occur in
A. armature alone
B. pole faces alone
C. both armature and pole faces
D. yoke alone

... Answer is (C)



52. The open circuit voltage of a de compound generator is 200 V. At full load, the terminal voltage
A. will always be 200 V
B. will always be less than 200 V
C. will always be greater than 200 V
D. may be greater than or less than 200 V

... Answer is (B)


53. For most of the applications
A. dc shunt generator is more popular than dc series generator
B. dc series generator is more popular than dc shund generator
C. both dc series and shunt generators are equally popular
D. dc compound generator is most popular

... Answer is (A)



54. Equalizer connections are required when paralleling two
A. bipolar genearators
B. shunt generators
C. series generators
D. compound generators

  ... Answer is (D)


55. In case of parallel operation of compound generators, for proper division of load from no load to full load, it is essential that
A. the regulation of each armature should be the same
B. their series field resistances should be equal
C. their ratings should be equal
D. none of these
Answer is (A)


56. A series generators is provided with diverter and is delivering its rated current. If the diverter switch is opened, the terminal voltage
A. will increase
B. will decrease
C. will remain the same
D. may increase or decrease

  ... Answer is (A)



57. In Hopkinson test on two shunt machines
A. the field currents of the two machines are equal
B. the field current of the generator is more than that of motor
C. the field current of the generator is less than of motor
D. none of these

  ... Answer is (B)


58. Critical resistance of dc generator is proportional to
A. N
B. 1/N²
C. 1/N
D. N

... Answer is (D)


59. In separately excited dc generator supplying rated load, the armature reaction

A. is always absent
B. is always present
C. may be sometimes present
D. none of these
  ... Answer is (B)


60. With flux remaining constant, if the speed of a shunt dc generator is doubled, its generated emf
A. doubles
B. becomes half
C. remain unchanged
D. become 4 times as large

  ... Answer is (A)



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