125+ Alternator Objective Questions and Answers

In this article, we shared the alternator objective questions and answers for electrical and electronics engineers.

Alternator Objective Questions

Alternator Objective Questions and Answers

The below list provides all the multiple-choice questions related to the electrical alternators.

Answers are available at the bottom of the article.

1. If the voltage of one of the two machines running in synchronism is suddenly increased

A)none of these answers
B)synchronizing torque will be produced to restore further synchronism
C)the machines will burn
D)both machines will stop

2. What is the largest size of alternator being manufactured in India?

A)210 MW
B)500 MW
C)110 MW
D)250 MW

3. In air-crafts, alternators have an operating frequency of

A)50 Hz
B)60 Hz
C)800 Hz
D)400 Hz

4. An alternator running in parallel with other alternators all having automatic voltage regulators is to be taken off the bus. The usual procedure before opening the switch is to

A)reduce the power fed to the prime mover
B)reduce alternator excitation
C)none of these answers
D)increase alternator excitation

5. Salient pole type rotors as compared to cylindrical pole type are

A)smaller in diameter and larger in axial length
B)large in diameter as well as axial length
C)larger in diameter and smaller in axial length
D)small in diameter as well as axial length

6. Which of the following is a prime mover?

A)Steam turbine
B)Electric heater
C)None of these answers
D)Solar energy

7. As the load power factor of an alternator becomes more leading, the value of generated voltage required to give rated terminal voltage

A)varies with rotor speed
C)remains unchanged

8. In a cylindrical rotor how much portion of the rotor is wound?

B)Two third
D)One third

9. Harmonic component of generated e.m.f. will be more in

A)short pitch coil
B)long-pitch coil
C)full-pitch coil
D)none of these answers

10. Salient pole rotors are used where

A)low and medium speed prime-movers are available
B)high speed prime movers are available
C)floor space is available in plenty
D)high frequency current is required

11. 4 pole 1500 r.p.m. alternator will generate e.m.f. at

A)20 Hz
B)60 Hz
C)40 Hz
D)50 Hz

12. An exciter for a generator is a

A)shunt generator
B)series generator
C)none of these answers
D)series motor
E)shunt motor

13. The load between two steam-driven alternators operating in parallel may be adjusted by varying

A)steam supply to their prime movers
B)field strengths of the alternators
C)power factors of the alternators
D)speed of the alternators

14. An infinite bus bar has

A)constant frequency and variable voltage
B)variable frequency and variable voltage
C)infinite frequency and infinite voltage
D)constant frequency and constant voltage

15. In a large generator, dampers

A)reduce voltage fluctuations
B)none of these answers
C)increase stability
D)reduce frequency fluctuations

16. The Poter’s triangle separates the

A)iron losses and copper losses
B)stator voltage and rotor voltage
C)armature leakage reactance and armature reaction m.m.f.
D)field m.m.f. and armature m.m.f.

17. Unlike D.C. generator kW rating, alternators are rated in


18. Which of the following is not an integral part of the synchronous generator system?

A)Protection system
B)Distribution system
C)Excitation system
D)Prime mover

19. In a synchronous machine, all of the following losses are fixed except

A)copper loss
B)bearing friction loss
C)core loss
D)windage loss

20. The regulation of an alternator is likely to be negative in the case of

A)leading power factor of the load
B)lagging power factor of the load
C)high speed alternators
D)low speed alternators

21. For parallel operation, A.C. polyphase alternators must have the same

A)kVA rating
D)voltage rating

22. The slip rings employed in a 3-phase alternator in the hydro station are insulated for

A)full armature voltage
B)low voltage
C)very low voltage
D)extra high tension voltage

23. When an alternator is supplying unity power factor load, the armature reaction will produce

A)distortion of the main field
B)demagnetisation of the main field
C)none of these answers
D)magnetization of the main field

24. Hydrogen is used in large alternators mainly to

A)cool the machine
B)strengthen the magnetic field
C)reduce distortion of waveform
D)reduce eddy current losses

25. Alternators, nowadays, are designed to have poor regulation because

A)we employ automatic voltage regulators
B)it limits the value of short circuit current
C)none of these answers
D)it reduces the construction cost

26. Two alternators ‘1’ and ‘2’ are share an inductive load equally. If the excitation of alternator ‘1’ is increased

A)alternator ‘2’ will deliver more current and alternator ‘1’ will deliver less current
B)both will continue to share load equally
C)alternator ‘2’ will deliver less current and alternator ‘1’ will deliver more current
D)both will deliver more current

27. What kind of rotor is most suitable for turbo-alternators that are designed to run at high speed?

A)Either Salient pole type or Non-salient pole type
B)Non-salient pole type
C)Salient pole type
D)None of these answers

28. Which fractional pitch will eliminate the seventh harmonic from the voltage waveform of an alternator?

C)None of these answers

29. An alternator operating at a lower voltage, for the same power rating, will be

A)more efficient
B)larger in size
D)less noisy

30. In an alternator terminal voltage rise will be more

A)when lagging load is thrown off
B)when the leading load is thrown off
C)when unity power factor load is thrown off
D)none of these answers

31. Alternators are usually designed to generate

A)variable frequencies
B)definite frequencies
C)definite power factor
D)definite currents

32. For the alternators operating in parallel, if the load shared by one of them is to be increased, its field excitation is

A)to be kept constant but input torque should be decreased
B)to be weakened keeping input torque the same
C)to be kept constant but input torque should be increased
D)to be strengthened keeping input torque the same

33. The regulation of an alternator is

A)the variation of terminal voltage under the condition of maximum and minimum excitation
B)the increase in terminal voltage when the load is thrown off
C)the change in terminal voltage from lagging power factor to leading power factor
D)none of these answers
E)the reduction in terminal voltage when the alternator is loaded

34. Which of the following prime-movers is the Ieast efficient?

A)Steam engine
B)Steam turbine
C)Gas turbine
D)Diesel engine

35. Dirt accumulation in generators can cause all of the following except

A)low power factor
C)poor voltage regulation

36. In a star connected armature winding

A)none of these answers
B)phase voltage contains 3rd harmonic e.m.f. but live voltage does not contain it
C)phase voltage does not contain third harmonic e.m.f. as line voltage also does not contain it
D)phase voltage contains 3rd harmonic e.m.f. as live voltage also contains third harmonic component

37. In a larger generator dampers

A)reduce voltage fluctuations
B)reduce frequency fluctuations
C)increase stability
D)none of these answers

38. Due to which of the following- reasons concentrated windings are not used in alternators?

A)Concentrated windings require deep slots for accommodation which leads to increased armature leakage and reactance
B)Concentrated windings increase voltage harmonics
C)Concentrated windings increase the copper-to-iron ratio thereby decreasing the capacity
D)Concentrated windings decrease induced e.m.f./phase

39. If the space flux distribution is nonsinusoidal, e.m.f. induced in the distributed winding

A)will be equally non-sinusoidal
B)none of these answers
C)will be more sinusoidal than flux distribution
D)will be less sinusoidal than flux distribution

40. Zero power factor method for an alternator is generally used to determine

A)efficiency of alternator
B)voltage regulation of the alternator
C)the synchronous impedance of the alternator
D)none of these answers

41. Synchronous impedance method gives more regulation as compared to ampere turn method because

A)none of these answers
B)the saturation effect is ignored in the synchronous impedance
C)armature reaction is considered negligible
D)the saturation effect is taken into account in the synchronous impedance method

42. An exciter is nothing but a


43. In an alternator, the pitch factor is the ratio of the e.m.fs. of

A)distributed winding to full pitch winding
B)full pitch winding to short pitch winding
C)full pitch winding to concentrated winding
D)short pitch coil to full pitch coil

44. The power factor of an alternator is determined by its


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

A)kW will be changed
B)kVA will be lagging
C)kVA will be leading
D)the power factor of the load remains constant

46. In an alternator zero power factor method is used to find the

A)voltage regulation
B)synchronous impedance
D)armature resistance

47. The permissible duration for which a generator of rated frequency 50 Hz can run at 46 Hz is

B)one cycle
C)none of these answers
D)one second
E)one minute

48. A commercial alternator has

A)rotating armature and stationary field
B)both armature and field fixed
C)stationary armature and rotary field
D)both armature and field rotary

49. Where the terminal voltage of an alternator falls on the throwing off the load, it indicates that the load is purely

D)none of these answers

50. 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 motor
C)synchronous motor
D)asynchronous generator

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

A)the active component of the output is changed
B)the reactive component of the output is changed
C)the power factor of the load remains constant
D)none of these answers

52. Generated e.m.f. for same field current and double speed will be

A)more than double
C)less than double

53. The speed of a 4-pole 60 Hz synchronous machine will be

A)1800 r.p.m.
B)3600 r.p.m.
C)2400 r.p.m.
D)3000 r.p.m.

54. Which harmonic will be totally eliminated in an alternator by using a fractional pitch of 4/5?


55. Large-diameter salient-pole rotors have short axial length mainly because

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

56. Alternator of a central power station will have

A)none of these answers
B)revolving armature winding
C)revolving field winding
D)either revolving field winding or revolving armature winding

57. Two alternators are to be put in parallel. Which of the following factors should be identical for both?

C)Phase sequence
D)All of these answers

58. A lower voltage alternator, for the same power rating, will be

A)larger in size
B)operating at high r.p.m.
C)more efficient
D)more costly

59. Fleming’s left-hand rule may be applied to an electric generator to find out the direction of

A)magnetic field
B)none of these answers
C)rotor rotation
D)induced e.m.f.

60. For a 3-phase winding with 5 slots per pole per phase and with a coil span of 12 slot pitch, the value of pitch factor is


61. In an alternator one of the advantages of distributing the winding is to

A)reduce harmonics
B)save on copper
C)improve voltage waveform
D)reduce noise
E)none of these answers

62. The fictitious part of synchronous reactance takes care of

A)armature reaction
B)voltage regulation
C)none of these answers
D)inductive reactance

63. Turbo-alternators usually have

A)8 poles
B)2 poles
C)4 poles
D)12 poles

64. When the speed of an alternator increases

A)the frequency changes
B)the frequency increases
C)the frequency decrease
D)the frequency remains same

65. The frequency of voltage generated in large alternators is

A)in kilo cycles
B)in mega cycles
C)60 Hz
D)50 Hz

66. The maximum current that can be supplied by an alternator depends on

A)speed of the exciter
B)exciter current
C)strength of the magnetic field
D)number of poles

67. The power drawn by the prime-mover of an alternator, under no-load conditions, goes to

A)produce power in armature
B)meet copper losses both in armature and rotor windings
C)meet no-load losses
D)produce e.m.f. in armature winding

68. When a three-phase alternator supplies capacitive load, armature reaction flux will be

A)helping the main magnetic field
B)opposing the main magnetic field
C)none of these answers
D)either opposing the main magnetic field or helping the main magnetic field

69. Regulation of an alternator supplying resistive or inductive load is

A)none of these answers
B)the saturated synchronous impedance
C)the saturated synchronous impedance
D)either the saturated synchronous impedance or the saturated synchronous impedance

70. 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 a synchronous motor and will rotate in the same direction
B)behave as an induction motor but will rotate in an opposite direction
C)get burnt
D)none of these answers

71. Regulation of an alternator supplying leading load is

A)sometimes positive and sometimes negative depending upon load and power factor
B)always negative
C)always positive

72. In an alternator the armature reaction is mainly influenced by

A)short-circuit ratio
B)speed of the alternator
C)total current drawn
D)the power factor of the load

73. An alternator is capable of delivering power at a particular efficiency. The frequency can be increased by

A)increasing the armature speed
B)increasing the current supplied to the field electromagnets
C)reversing the armature rotation
D)reversing the field polarity

74. The advantage of salient poles in an alternator is

A)the adaptability of low and medium speed operation
B)reduced noise
C)reduced windage loss
D)reduced bearing loads and noise

75. In the case of turbo-alternators the rotor is usually made of

A)forged ​ steel
B)manganese steel
C)cast iron
D)laminated stainless steel

76. The number of poles in turbo-alternator is usually


77. Modern 3-phase alternator of a central power station will have generated voltage of

A)230 V
B)11 kV
C)400 V
D)132 kV

78. In turbo-alternators, smooth cylindrical type rotors used have long axial lengths because

A)it gives smooth running of the rotor
B)centrifugal force is reduced
C)it reduces windage loss
D)number of armature conductors being less, they have to be necessarily long for generating the required voltage

79. In an alternator, for a coil having a span of 2/3 of pole pitch, the coil span factor will be


80. In an alternator, armature reaction is considered equivalent to

A)fictitious reactance
B)fictitious conductance
C)fictitious resistance
D)fictitious impedance

81. Leakage reactance of the armature of a salient pole synchronous machine which varies with the position of the rotor is due to

A)leakage flux which comes out of slot, teeth, crosses the air gap and enters pole faces
B)none of these answers
C)leakage flux which remains within the slot
D)leakage flux of end connections

82. Dirt accumulation in generators can cause

A)poor voltage regulation
B)all of these answers

83. Due to which of the following reasons, for aircraft alternators high frequency is used?

A)To compensate for high speeds
B)None of these answers
C)To free the systems from external disturbance
D)To compensate for high altitudes
E)To reduce the bulk

84. In power generating stations (Thermal stations), the usual number of poles employed in alternators are

A)thirty two
B)none of these answers
C)forty eight
D)twenty four

85. Which of the following organizations is engaged in the manufacture of large size alternators for power plants in India?

A)National Thermal Power Corporation Ltd.
B)Department of Science and Technology
C)Bharat Heavy-Electricals Ltd.
D)Electricity Authority of India

86. Which of the following methods is best for finding the voltage regulation?

A)All are equally good
B)Potier triangle method
C)Synchronous impedance method
D)M.M.F. method

87. An alternator driven by a Francis hydraulic turbine is a ____alternator

A)low or medium speed
B)high speed
C)medium speed
D)low speed

88. Which of the following relays come into operation in the event of the failure of the prime-mover connected to the generator?

A)Reverse power relay
B)None of these answers
C)All of these answers
D)Buchholz relay
E)Differential relay

89. When two alternators are running in exact synchronism, the scychronising power will be

A)none of these answers
D)sum of the output of two

90. In order to reduce the harmonics in the e.m.f. generated in an alternator

A)slots are skewed
B)salient pole tips are chamfered
C)winding is well distributed
D)all of these answers
E)none of these answers

91. Which of the following coils in an alternator will have e.m.f. closer to sine waveform?

A)Concentrated winding in full pitch coils
B)Distributed winding in full pitch coils
C)Concentrated winding in short pitch coilsated winding in short pitch coils
D)Distributed winding in short pitch coils

92. A stationary alternator should not be connected to a live bus-bar because it

A)will decrease but-bar voltage though momentarily
B)none of these answers
C)will disturb generated e.m.fs. of other alternators connected in parallel
D)will get short-circuited
E)is likely to run as a synchronous motor

93. The rotor preferred for alternators applied to hydraulic turbines are

A)salient pole type
B)any of these answers
C)solid rotor type
D)cylindrical rotor type

94. Salient pole type alternators are generally used on

A)low voltage alternators
B)high speed primemovers
C)low and medium speed primemovers
D)hydrogen cooled primemovers

95. The dark and bright lamp method is used for

B)transfer of load
C)phase sequence
D)balancing of load

96. Turbo-alternators are generally used to run at

A)5000 r.p.m.
B)15000 r.p.m.
C)3000 r.p.m
D)1500 r.p.m.

97. Turbo-rotor is made up of

A)none of these answers
C)large spider to which laminated pole shoes are secured
D)solid steel forging having milled slots for the field winding

98. In an alternator short-circuit current is limited by

A)none of these answers
B)either the saturated synchronous impedance or the saturated synchronous impedance
C)the saturated synchronous impedance
D)the saturated synchronous impedance

99. Which of the following conditions does not have to be met by alternators working in parallel?

A)The terminal voltage of each machine must be the same
B)Alternators must operate at the same frequency
C)Machines must have the same phase rotation
D)The machines must have equal kVA ratings

100. One of the super-thermal power stations is being located at,


101. In which coil the harmonic component of the generated e.m.f. will be more?

A)Full pitch coil
B)Long pitch coil
C)Short pitch coil
D)Same in all coils

102. For parallel operation of the two alternators, the desirable feature is that both should have

A)more of resistance as compared to synchronous reactance
B)same reactance
C)less of resistance as compared to synchronous reactance
D)same resistance

103. In an alternator, the armature reaction will be completely magnetizing in case the load power factor is

A)zero lagging
D)zero leading

104. In an alternator, the frequency of voltage generated depends on

A)number of poles only
B)none of these answers
C)rotative speed only
D)both rotative speed only and number of poles only

105. Excessive windage loss and noise occur with

A)none of these answers
B)salient pole rotors
C)rotating armature
D)either rotating armature or salient pole rotors

106. Non-salient pole type of rotor construction is usually provided in the alternators used in

A)either of the above
B)hydropower stations
C)none of these answers
D)thermal power stations

107. In an alternator, the flux is 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 zero lagging
B)load power factor is 0.6 lagging
C)load power factor is zero leading
D)load power factor is unity

108. In an alternator, the stator frame serves

A)to hold the armature stampings
B)as a return path for the flux
C)to protect, the whole machine
D)to verticate the armature

109. If an alternator is operating at leading power factor, then it can be concluded that

A)the torque angle of the alternator has a negative value
B)the alternator is under-excited
C)the alternator is over-excited
D)the residual magnetism of the poles is zero

110. The synchronous impedance method of finding voltage regulation of an alternator is called the pessimistic method because

A)it is simplest to perform and compute
B)armature reaction is wholly magnetizing
C)none of these answers
D)it gives a regulation value higher than is actually found by direct loading

111. Unbalanced three-phase stator currents cause

A)all of these answers
C)heating of rotor
D)double frequency currents in the rotor

112. The speed of a salient pole machine is nearly

A)500 r.p.m.
B)1000 r.p.m.
C)1500 r.p.m.
D)3000 r.p.m.

113. For a given output steam turbo-alternators are much smaller in size than water turbine alternators because

A)all of these answers
B)steam turbo-alternators run at high speed
C)steam turbo-alternators have long rotors
D)steam turbo-alternators are built with smaller capacities

114. When two alternators are running in parallel, their kVAR load share and kW load share are changed by changing their

A)excitation and excitation
B)excitation, driving torque respectively
C)driving torque, excitation respectively
D)driving torque, driving torque respectively

115. If two alternators are running in proper synchronism and the voltage of one machine is suddenly increased

A)both machines will stop
B)none of these answers
C)one machine will stop
D)synchronizing torque will be produced to restore further synchronism

116. An alternator coupled to which prime mover will usually have the highest rotating speed?

A)Reciprocating diesel engine
B)Francis turbine
C)Steam turbine
D)Steam engine

117. Damper winding on alternator results in all of the following except

A)elimination of harmonic effects
B)absorption of energy of oscillations when operating in parallel with other alternators
C)suppression of spontaneous hunting- when supplying power to transmission line with high resistance to reactance ratio
D)increases instability of the machine

118. To obtain sinusoidal flux distribution

A)none of these answers
B)chamfering of poles is done in turbo-alternators only
C)chamfering of poles is done in turbo-alternators only
D)either chamfering of poles is done in turbo-alternators only or chamfering of poles is done in turbo-alternators only

119. ___ plays an important role in overspeed protection of a generator?

A)Differential protection
C)Over-current relay

120. In alternators, the standard practice nowadays is to have

A)rotating field
B)rotating armature
C)either rotating field or a rotating armature
D)none of these answers

121. The distribution factor, in alternators, is defined as the ratio of e.m.fs. Of

A)distributed winding to full pitch winding
B)distributed winding to concentrated winding
C)concentrated winding to distributed winding
D)full pitch winding to distributed winding

122. Voltage regulation obtained by synchronous impedance method is

A)equal to that given by actual tests
B)none of these answers
C)more than that given by actual tests
D)less than that given by actual tests

123. 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 load
C)change its frequency
D)reduce its speed

124. The power factor of an alternator is determined by its

A)prime mover
E)none of these answers

125. In an alternator, when the load power factor is unity

A)none of these answers
B)the armature flux will be demagnetising
C)the armature flux will reduce to zero
D)the armature flux will be crossmagnetising
E)the armature flux will have square wave form

126. In an alternator field, the effect of cross magnetization is to make the output

B)true sinusoidal
C)free from harmonics
D)none of these answers

127. Three-phase alternators are invariably star-connected because

A)less turns of wire are required
B)higher terminal voltage is obtained
C)small conductors can be used
D)magnetic losses are the minimum

128. Which of the following prime mover is least efficient?

A)Steam engine
B)Petrol engine
C)Diesel engine
D)Gas turbine

129. At leading power factor, the armature flux in an alternator

A)distorts the rotor flux
B)does not affect the rotor flux
C)aids the rotor flux
D)opposes the rotor flux

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

A)unity power factor
B)lagging to leading power factor
C)leading power factor
D)any of these answers
E)lagging power factor

131. If the driving force of both the alternators running in parallel is changed, this will result in a change in

A)all of these answers
B)generated voltage
C)back e.m.f.

132. The speed of an alternator is changed from 3000 r.p.m. to 1500 r.p.m. The generated e.m.f./phase will become

D)one fourth

133. Which of the following is the common synchronous speed in r.p.m. between 50 Hz and be 60 Hz alternators?


134. If two alternators are running in parallel and the excitation of one of the alternators is increased, then

A)machine with excess excitation will burn
B)power output will decrease
C)none of these answers
D)the wattless component will change
E)both machines will start vibrating

135. If the steam supply of an alternator running in parallel with another identical alternator is increased keeping its excitation constant, then

A)it would over-run the other alternator
B)the power factor would be decreased
C)it will supply a greater portion of the load
D)its rotor will fall back in phase with respect to the other machine

136. The choice of field construction, in an alternator, is basically determined by

A)the generated voltage needed by the customers
B)supply frequency required by the consumers
C)comparative cost of the field systems
D)the kind of energy source available in the geographic location

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