Alternator MCQ PDF Download

1. In a synchronous machine, if the field flux axis is ahead of the armature field axis in the direction of rotation, the machine operating is

(a) synchronous motor.
(b) synchronous generator.
(c) asynchronous motor.
(d) asynchronous generator.

2. The armature of an alternator

(a) is a stationary member.
(b) is a revolving member.
(c) is the frame.
(d) consists of the winding into which current is induced.

3. In modern alternators, the rotating part is

(a) field system.
(b) armature.
(c) armature as well as field system.
(d) none of the above.

4. The current from the stator of an alternator is taken out to the external load circuit through

(a) slip rings.
(b) commutator segments.
(c) solid connections.
(d) carbon brushes.

5. Which one of the following is the primary reason for placing field on rotor in an alternator?

(a) Small power in the field circuit.
(b) Insulation of high voltage is made easy on stator than on rotor.
(c) Large power in stator.
(d) Large current in stator. [U.P.S.C. I.E.S. 2004]

6. Which type of alternator is used in hydroelectric power stations?

(a) Non-salient pole alternator.
(b) Turbo generator.
(c) Salient pole alternator.
(d) Steam turbine alternator. [U.P.S.C. I.E.S. 2004]

7. Consider the following statements.

The synchronous generators used in thermal powe stations have

1. Cylindrical rotors.
2. Slip rings and brushes.
3. Laminated rotor.
4. Stator slots in the multiples of 6.
5. 3-phase stator-connected windings.

Which of these statements are correct?
(a) 1, 2, 3 and 4
(b) 1, 2, 3 and 5
(c) 3, 4 and 5
(d) 1, 2, 4 and 5 [U.P.S.C. I.E.S. 1999]

8. In a synchronous machine, the stator frame serves the purpose of

(a) holding the armature stampings in position and also in some cases for circulating cold water for cooling.
(b) insulaing the armature windings.
(c) providing path to the magnetic flux.
(d) protecting the whole machine.

9. In a synchronous machine, the stator frame is made of

(a) stainless steel.
(b) CRGOS.
(c) cast iron or welded steel plates.
(d) laminated silicon steel.

10. The stator core stampings also have openings which make ……….. ventilating ducts to provide efficient cooling.

(a) axial
(b) radial
(c) axial as well as radial
(d) none of the above.

11. The open slots are more commonly used in the stator of a synchronous machine as

(a) the inductance of the winding is less.
(b) they permit the placement of form wound and insulated coils giving least expensive and more satisfactory.
(c) both (a) and (b).
(d) none of these.

12. The slip rings employed in a 3-phase synchronous machine are insulated for

(a) output rated voltage.
(b) low voltage.
(c) very low voltage.
(d) very high voltage.

13. In a large synchronous generator, the damper winding is provided for

(a) absorption of energy of oscillations when operating in parallel with another alternator.
(b) suppression of spontaneous hunting when supplying power to a transmission line with high resistance/reactance ratio.
(c) providing a low resistance path for the currents due to unbalancing of voltages.
(d) all of the above.

14. Squirrel-cage bars placed in the rotor pole faces of an alternator help reducing hunting

(a) above synchronous speed only.
(b) below synchronous speed only.
(c) above and below synchronous speeds both.
(d) none of the above. [A.M.I.E. Sec B. 1993; 1997]

15. Hydro-generators are generally employed to run at ……… rpm.

(a) 500
(b) 1,000
(c) 1.500
(d) 3,000

16. In case of turbo-alternators, rotor is made of

(a) forged steel.
(b) cast iron.
(c) stainless steel.
(d) manganese steel.
(e) laminated silicon steel.

17. The salient pole rotors have

(a) two or four projecting poles carrying the field coils.
(b) a large number of projecting poles carrying the field coils.
(c) thick steel laminations riveted together and fixed to the rotor by a dove-tail joint.
(d) pole faces usually provided with slots for damper windings.
(e) all of the above except (a).

18. In salient pole field structure, the pole shoes cover about ……….. of pole pitch.

(a) one-third
(b) one half
(c) two-third
(d) whole

19. Larger diameter salient pole rotors have shorter axial length because

(a) it occupies much less space.
(b) it saves lot of copper in stator winding.
(c) it reduces weight of the rotor.
(d) number of conductors held in large circumference of rotor is very large and so they need not be long.

20. In a salient pole synchronous machine, the air gap is

(a) uniform under the whole pole shoe.
(b) least under the middle of the pole shoe and increases outwards.
(c) largest under the middle of the pole shoe and decreases outwards.
(d) least at one end of the pole shoe and increases to the maximum value at the other end. [U.P.S.C. IES. 2004]

21. The number of poles on turbo-alternator is usually

(a) 2
(b) 4
(c) 6
(d) 8

22. To obtain sinusoidal flux distribution, chamfering of poles is done in

(a) salient-pole alternators only.
(b) smooth cylindrical pole alternators only.
(c) both of the above.
(d) none of these.

23. The salient pole rotors are not suitable for high speed turbo-generators due to

(a) excessive bearing friction.
(b) undesirable mechanical oscillations.
(c) high centrifugal force and windage loss.
(d) large eddy current losses.

24. In turbo-alternators, smooth cylindrical rotors have very long axial length because it

(a) reduces friction and windage loss.
(b) reduces centrifugal force.
(c) number of conductors being less, they have to be necessarily long for generating the required voltage.
(d) none of the above.

25. In cylindrical rotor ……….. portion of rotor is wound.

(a) one-third
(b) two-third
(c) one-half
(d) whole

26. The maximum possible speed at which an alternator can be driven to generate 50 Hz and 4,000 V is

(a) 4,000 rpm.
(b) 3,600 rpm.
(c) 3,000 rpm.
(d) 1,500 rpm.

27. Two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively. The highest speed of the alternators is

(a) 3,600 rpm.
(b) 3,000 rpm.
(c) 600 rpm.
(d) 500 rpm.

28. A three-phase 50 Hz, 11 kV and 37.5 MW at 0.9 p.f. capacity synchronous generator has its stator bore diameter of 765 cm and an axial core length of 80 cm. For which power plant this generator is suitable?

(a) Thermal coal fired plant.
(b) Hydroelectric power plant.
(c) Nuclear power plant.
(d) Pumped storage power plant. [U.P.S.C. IES. 2009]

29. Tne most appropriate operating speeds in rpm of generators used in Thermal, Nuclear and Hydropower plants would respectively be

(a) 3000, 300 and 1500
(b) 3000, 3000 and 300
(c) 1500, 1500 and 3000
(d) 1000, 900 and 750 [U.P.S.C. I.E.S. 1994]

30. The aircraft alternators are designed to generate emf of high frequency of 400 Hz in order to

(a) reduce the bulk.
(b) compensate for high speeds.
(c) make the systems free from external disturbances.
(d) all of the above.

 

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