Alternator MCQ | Electricalvoice

Alternator MCQ

1. When the load power factor is unity, the effect of armature reaction on the main field flux of an alternator is

  1. distortional
  2. magnetizing
  3. demagnetizing
  4. no effect
Answer. a

2. By matching which of the following individual machines, the load frequency control is achieved?

  1. Reactive power
  2. Turbine inputs
  3. Generated voltage
  4. Turbine and generator ratings
Answer. b

3. At lagging loads, the effect of armature reaction in an alternator is?

  1. Magnetizing
  2. Neutralizing
  3. Cross-magnetizing
  4. Demagnetizing
Answer. d

4. Magnetic field poles are the ________ part of an alternator.

  1. Static
  2. Rotary
  3. Reciprocating
  4. Circuital
Answer. b

5. Variable losses in alternator is determined by

  1. iron losses
  2. iron losses + armature losses
  3. armature losses + series field losses
  4. iron losses + mechanical losses
Answer. c

6. If a P-pole alternator rotates N completes rotations, it produces __________ cycles of generated voltage. (As N in the number of rotations made per second)

  1. NP/2
  2. P/2N
  3. 2N/P
  4. 2NP
Answer. a

7. A 400 MVA, 20 kV synchronous generator has 0.3 per unit. synchronous reactance. The per unit synchronous reactance on the base values of 200 MVA and 40 kV is

  1. 2.2 p.u.
  2. 2.7 p.u.
  3. 2.6 p.u.
  4. 2.4 p.u.
Answer. d

8. Which one of the following is not a necessary condition to be satisfied for synchronizing an incoming alternator to an already operating alternator?

  1. Same voltage
  2. Same frequency
  3. Same prime mover speed
  4. Same phase sequence
Answer. c

9. A 200 MVA, 11kV, 3-phase, 6-pole synchronous generator has an inertia constant H equal to 2 MJ/MVA. What will be the magnitude of storage energy at synchronous speed?

  1. 200 MJ
  2. 100 MJ
  3. 2 MJ
  4. 400 MJ
Answer. d

10. In a 360 kV network, 280 kV is recorded at a 360 kV bus. The reactive power absorbed by a shunt rated for 50 MVAR, 360 kV connected at the bus is

  1. 40.8 MVAR
  2. 30.24 MVAR
  3. 33.67 MVAR
  4. 41.55 MVAR
Answer. b

11. When an alternator is running on no-load the power supplied by the prime mover is mainly consumed to

  1. produce induced emf in the armature winding
  2. meet iron losses
  3. meet copper losses
  4. meet all no-load losses
Answer. d

12. An alternator is said to be over-excited when it is operating at

  1. unity power factor
  2. leading power factor
  3. lagging power factor
  4. lagging to leading power factor
Answer. c

13. If the input to the prime mover of an alternator is kept constant but the excitation is changed, then

  1. the reactive component of the output is changed
  2. the active component of the output is changed
  3. the power factor of the load remains constant
  4. the power factor of the load reduces
Answer. a

14. Fleming’s left-hand rule may be applied to an electric generator to find out

  1. the direction of rotor rotation
  2. the polarity of induced emf
  3. the direction of induced emf
  4. the direction of the magnetic field
Answer. c

15. The number of electrical degrees passed through in one revolution of a six-pole synchronous alternator is

  1. 360
  2. 720
  3. 1080
  4. 2160
Answer. c

16. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycles per second will be

  1. 120
  2. 110
  3. 100
  4. 50
Answer. c

17. An alternator is generating power at 210 V per phase while running at 1500 rpm. If the need for the alternator drops to 1000 rpm, the generated voltage per phase will be

  1. 180 V
  2. 150 V
  3. 140 V
  4. 105 V
Answer. c

18. The frequency of voltage generated in an alternator depends on

  1. number of poles
  2. rotative speed
  3. number of poles and rotative speed
  4. number of poles, rotative speed, and type of winding
Answer. c

19. Salient poles are generally used on

  1. High-speed prime movers only
  2. Medium speed prime movers only
  3. Low-speed prime movers only
  4. Low and medium speed prime movers
Answer. d

20. Which kind of rotor is most suitable for turbo alternators which are designed to run at high speed?

  1. Salient pole type
  2. Non-salient pole type
  3. Both (a) and (b) above
  4. None of the above
Answer. b
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