DC Generator MCQ

1. A 220 V dc compound generator connected in long-shunt mode has the following parameters: Ra = 0.1 Ω, Rsh = 80 Ω, Rseries = 0.05 Ω. For a load of 150 A at rated terminal voltage, the induced emf of the generator should nearly be

  1. 243 V
  2. 233 V
  3. 262 V
  4. 251 V
Answer
Answer. a

2. A 24-slot, 2-pole, lap-wound dc machine has 18 turns per coil. The average flux density per pole is 1 Tesla. The effective length of the machine is 20 cm and the radius of the armature is 10 cm. The magnetic poles cover 80% of the armature periphery. For armature angular velocity (ωm) of 183.2 rad/sec, the induced emf in the armature winding is nearly

  1. 1050 V
  2. 585 V
  3. 1465 V
  4. 1260 V
Answer
Answer. d

3. For a d.c. shunt generator to self excite, the conditions to be satisfied are that there must be some residual magnetism in the field magnet, it must be in the proper direction and the shunt field resistance must be

  1. above the critical field resistance
  2. equal to the critical field resistance
  3. less than the armature resistance
  4. less than the critical field resistance
Answer
Answer. d

4. The induced emf in the armature conductor of a D.C. machine is

  1. Sinusoidal
  2. Trapezoidal
  3. Rectangular unidirectional
  4. Triangular
Answer
Answer. d

5. A dc machine having a symmetrical closed-circuit armature winding and a sinusoidal air gap flux density distribution, will have a sinusoidal voltage induced in the individual coils. The resultant brush-to-brush voltage will have a waveform

  1. Sinusoidal with the negative half
  2. Unidirectional and constant without
  3. Unidirectional and constant with ripples superimposed
  4. Sinusoidal positive half and zero negative half, in each cycle
Answer
Answer. c

6. Consider the following factors for a dc machine:

  1. Interpole
  2. Armature resistance
  3. Reduction in field current

Which of the above factors are responsible for decrease in terminal voltage of a shunt generator?

  1. i and ii only
  2. ii and iii only
  3. i and iii only
  4. i, ii and iii
Answer
Answer. b

7. The internal characteristic of a dc generator is plotted between the

  1. armature current and voltage generated after armature reaction.
  2. field current and voltage generated at no load.
  3. field current and voltage generated on load
  4. armature current and voltage generated at the output terminals.
Answer
Answer. a

8. The internal characteristics of a dc generator is plotted between the

  1. field current and voltage generated at no load.
  2. armature current and voltage generated on load.
  3. armature current and voltage generated after armature reaction.
  4. field current and voltage generated on load.
Answer
Answer. c

9. In dc machines, the field-flux axis and armature-mmf axis are respectively along

  1. direct axis and indirect axis
  2. direct axis and inter-polar axis
  3. quadrature axis and direct axis
  4. quadrature axis and inter-polar axis
Answer
Answer. b

10. In a dc machine, for the same number of slots and same current in the armature conductor, which one of the following will induce higher emf?

  1. Lap winding
  2. Wave winding
  3. Compensating winding
  4. Pole winding
Answer
Answer. b
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