Alternator MCQ

1. Overheating of generator’s winding

(a) reduces life of the machine
(b) does not have any significant effect
(c) reduces generated voltage
(d) reduces power factor


Answer: (a) reduces life of the machine
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2. The maximum current that can be supplied by an alternator depends on

(a) exciter current
(b) strength of the magnetic field
(c) number of poles
(d) speed of the exciter


Answer: (d) speed of the exciter
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3. The regulation of an alternator is likely to be negative in case of

(a) lagging power factor of the load
(b) leading power factor of the load
(c) high speed alternators
(d) low speed alternators


Answer: (b) leading power factor of the load
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4. The regulation of an alternator is

(a) the increase in terminal voltage when load is thrown off
(b) the reduction in terminal voltage when alternator is loaded
(c) the variation of terminal voltage under the condition of maximum and minimum excitation
(d) the change in terminal voltage from lagging power factor to leading power factor
(e) none of the above


Answer: (a) the increase in terminal voltage when load is thrown off.
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5. An alternator driven by a Francis hydraulic turbine is a ………..alternator.

(a) low speed
(b) medium speed
(c) high speed
(d) low or medium speed


Answer: (d) low or medium speed.
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6. If two alternators are running in proper synchronism and the voltage of one machine is suddenly increased

(a) both machines will stop
(b) one machine will stop
(c) synchronizing torque will be produced to restore further synchronism
(d) none of the above


Answer: (c) synchronizing torque will be produced to restore further synchronism.
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7. If the steam supply of an alternator running in parallel with another identical alternator is increased keeping its excitation constant, then

(a) it will supply greater portion of the load
(b) the power factor would be decreased
(c) it would over-run the other alternator
(d) its rotor will fall back in phase with respect to the other machine


Answer: (a) it will supply greater portion of the load.
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8. An exciter for a generator is a

(a) shunt motor
(b) series motor
(c) shunt generator
(d) series generator


Answer: (c) shunt generator.
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9. Two alternators ‘1’ and ‘2’ sharing an inductive load equally. If the excitation of alternator ‘1’ is increased

(a) the alternator ‘2’ will deliver less current and alternator ‘1’ will deliver more current
(b) alternator ‘2’ will deliver more current and alternator ‘1’ will deliver less current
(c) both will deliver more current
(d) both will continue to share the load equally


Answer: (a) the alternator ‘2’ will deliver less current and alternator ‘1’ will deliver more current.
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10. Which of the following coils in an alternator will have e.m.f. closer to sine waveform ?

(a) Distributed winding in full pitch coils
(b) Distributed winding in short pitch coils
(c) Concentrated winding in full pitch coils
(d) Concentrated winding in short pitch coils


Answer: (b) Distributed winding in short pitch coils.
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11. The distribution factor, in alternators, is defined as the ratio of e.m.fs. of

(a) distributed winding to full pitch winding
(b) concentrated winding to distributed winding
(c) distributed winding to concentrated winding
(d) full pitch winding to distributed winding


Answer: (c) distributed winding to concentrated winding.
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12. As load power factor of an alternator becomes more leading the value of generated voltage required to give rated terminal voltage

(a) decreases
(b) increases
(c) varies with rotor speed
(d) remains unchanged


Answer: (a) decreases
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13. In an alternator, the flux created by the armature m.m.f. subtracts directly from the main flux for the following conditions of the load

(a) load power factor is unity
(b) load power factor is 0.6 lagging
(c) load power factor is zero lagging
(d) load power factor is zero leading


Answer: (c) load power factor is zero lagging.
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14. Synchronous impedance method of finding voltage regulation of an alternator is called pessimistic method because

(a) it is simplest to perform and compute
(b) it gives regulation value higher than is actually found by direct loading
(c) armature reaction is wholly magnetizing
(d) none of the above


Answer: (b) it gives regulation value higher than is actually found by direct loading.
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15. Two alternators are running in parallel. If the field of one of the alternators is adjusted it will

(a) change its power factor
(b) change its frequency
(c) reduce its speed
(d) change its load


Answer: (a) change its power factor
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16. In a synchronous machine. If the field flux axis is ahead of the armature field axis, in the direction of rotation, the machine is working as

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


Answer: (a) synchronous generator
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17. The advantage of salient poles in an alternator is

(a) reduced windage loss
(b) reduced bearing loads and noise
(c) reduced noise
(d) adaptability of low and medium speed operation


Answer: (d) adaptability of low and medium speed operation
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18. For parallel operation of the two alternators, desirable feature is that both should have

(a) same reactance
(b) same resistance
(c) more of resistance as compared to synchronous reactance
(d) less resistance as compared to synchronous reactance


Answer: (d) less resistance as compared to synchronous reactance.
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19. If two alternators are running in parallel and the excitation of one of the alternators is increased, then

(a) power output will decrease
(b) wattless component will change
(c) machine with excess excitation will burn
(d) both machines will start vibrating


Answer: (b) wattless component will change
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20. When an alternator is supplying unity power factor load, the armature reaction will produce

(a) distortion of the main field
(b) magnetization of the main field
(c) demagnetization of the main field
(d) none of the above


Answer: (a) distortion of the main field
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21. If the driving force of both the alternators running in parallel is changed, this will result in change in

(a) generated voltage
(b) frequency
(c) back e.m.f.
(d) all of the above


Answer: (b) frequency
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22. In an alternator, when the load power factor is unity

(a) the armature flux will be demagnetizing
(b) the armature flux will be cross-magnetizing
(c) the armature flux will reduce to zero
(d) the armature flux will have square wave form
(e) none of the above


Answer: (b) the armature flux will be cross-magnetizing.
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23. The Poiter’s triangle separates the

(a) stator voltage and rotor voltage
(b) field m.m.f. and armature m.m.f.
(c) armature leakage reactance and armature reaction m.m.f.
(d) iron losses and copper losses


Answer: (c) armature leakage reactance and armature reaction m.m.f.
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24. In an alternator zero power factor method is used to find the

(a) synchronous impedance
(b) efficiency
(c) armature resistance
(d) voltage regulation


Answer: (d) voltage regulation
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25. If the driving power from the prime-mover driving an alternator is lost but the alternator remains connected to the supply network and field supply is on, then the alternator will

(a) behave as an induction motor but will rotate in an opposite direction
(b) behave as a synchronous motor and will rotate in the same direction
(c) get burnt
(d) none of the above


Answer: (b) behave as a synchronous motor and will rotate in the same direction.
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26. In turbo-alternators, smooth cylindrical type rotors used have long axial length because

(a) it gives smooth running of the rotor
(b) it reduces windage loss
(c) centrifugal force is reduced
(d) number of armature conductors being less they have to be necessarily long for generating the required voltage


Answer: (d) number of armature conductors being less they have to be necessarily long for generating the required voltage.
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27. Large diameter salient-pole rotors have short axial length mainly because

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


Answer: (c) number of armature conductors held in the large circumference, rotor being very large, they need not be long.
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28. At leading power factor, the armature flux in an alternator

(a) distorts the rotor flux
(b) aids the rotor flux
(c) opposes the rotor flux
(d) does not affect the rotor flux


Answer: (b) aids the rotor flux
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29. Three-phase alternators are invariably star-connected because

(a) higher terminal voltage is obtained
(b) less turns of wire are required
(c) small conductors can be used
(d) magnetic losses are the minimum


Answer: (a) higher terminal voltage is obtained.
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30. Which of the following conditions does not have to be met by alternators working in parallel ?

(a) Alternators must operate at the same frequency.
(b) Machines must have the same phase rotation.
(c) The terminal voltage of each machine must be the same.
(d) The machines must have equal kVA ratings.


Answer: (d) The machines must have equal kVA ratings.
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31. The fictitious part of synchronous reactance takes care of

(a) inductive reactance
(b) armature reaction
(c) voltage regulation
(d) none of the above


Answer: (b) armature reaction.
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32. In an alternator, the voltage of field system is usually

(a) more than 1000 V
(b) between 400 V and 600 V
(c) less than 200 V
(d) none of the above


Answer: (c) less than 200 V
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33. In an alternator, pitch factor is the ratio of the e.m.fs. of

(a) full pitch winding to short pitch winding
(b) short pitch coil to full pitch coil
(c) distributed winding to full pitch winding
(d) full pitch winding to concentrated winding


Answer: (b) short pitch coil to full pitch coil.
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34. When two alternators are running in exact synchronism, the synchronizing power will be

(a) unity
(b) zero
(c) sum of the output of two
(d) none of the above


Answer: (b) zero
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35. In an alternator if the armature reaction produces demagnetization of the main field, the power factor should be

(a) unity
(b) zero, lagging load
(c) zero, leading load
(d) none of the above


Answer: (b) zero, lagging load
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Alternator MCQ

 

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