Synchronous Generator MCQ 1 147

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Multiple Choice Questions of Synchronous Generator (1-15):
1. In an alternator, voltage drops occurs in
(A) armature resistance only
(B) armature resistance and leakage reactance
(C) armature resistance, leakage reactance and armature reaction
(D) armature resistance, leakage reactance, armature reaction and earth
connections.

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2. The magnitude of various voltage drops that occur in an alternator,
depends on
(A) power factor of the load
(B) load current
(C) power factor x load current
(D) power factor x (load current)
2
.

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3. In an alternator, at lagging power factor, the generated voltage per
phase, as compared to that at unity power factor
(A) must be same as terminal voltage
(B) must be less than the terminal voltage
(C) must be more than the terminal voltage
(D) must be 1.41 time the terminal voltage.

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4. The power factor of an alternator depends on
(A) Load
(B) Speed of rotor
(C) Core losses
(D) Armature losses.

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5. Which kind of rotor is most suitable for turbo alternators which arc
designed to run at high speed ?
(A) Salient pole type
(B) Non-salient pole type
(C) Both (A) and (B) above
(D) None of the above.

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6. Salient poles are generally used on
(A) high speed prime movers only
(B) medium speed prime movers only
(C) low speed prime movers only
( D) low and medium speed prime movers.

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7. The frequency of voltage generated in an alternator depends on
(A) number of poles
(B) rotative speed
(C) number of poles and rotative speed
(D) number of poles, rotative speed and type of winding.

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Synchronous Generator : Multiple Choice Questions (1-15)
1 of 3

8. The frequency of voltage generated by an alternator having 8 poles and
rotating at 250 rpm is
(A) 60 Hz
(B) 50 Hz
(C) 25 Hz
(D) 16 2/3 Hz.

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9. An alternator is generating power at 210 V per phase while running at
1500 rpm. If the need of the alternator drops to 1000 rpm, the generated
voltage per phase will be
(A) 180 V
(B) 150 V
(C) 140 V
(D) 105 V.

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10. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC
voltage in cycles per second will be
(A)120
(B) 110
(C) 100
(D) 50.

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11. The number of electrical degrees passed through in one revolution of a
six pole synchronous alternator is
(A)360
:
(B)720
(C) 1080
(D)2160 .

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12. Fleming's left hand rule may be applied to an electric generator to find
out
(A) direction of rotor rotation
(B) polarity of induced emf
(C) direction of induced emf
(D) direction of magnetic field.

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13. If the input to the prime mover of an alternator is kept constant but the
excitation is changed, then the
(A) reactive component of the output is changed
(B) active component of the output is changed
(C) power factor of the load remains constant
(D) power factor of the load reduces.

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14. An alternator is said to be over excited when it is operating at
(A) unity power factor
(B) leading power factor
(C) lagging power factor
(D) lagging to leading power factor.

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15. When an alternator is running on no load the power supplied by the
prime mover is mainly consumed
(A) to meet iron losses
(B) to meet copper losses
(C) to meet all no load losses
(D) to produce induced emf in armature winding.

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16. As the speed of an alternator increases
(A) the frequency increases
(B) the frequency decreases
(C) the frequency remains constant but power factor decreases
(D) none of the above.

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17. For an alternator when the power factor of the load is unity
(A) the armature flux will have square waveform
(B) the armature flux will be demagnetising
(C) the armature flux will be cross-magnetising
(D) the armature flux will reduce to zero.

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18. The driving power from the prime mover driving the alternator is lost but
the alternator remains connected to the supply network and the field supply
also remains on. The alternator will
(A) get burnt
(B) behave as an induction motor but will rotate in the opposite direction
(C) behave as a synchronous motor and will rotate in the same direction
(D) behave as a synchronous motor but will rotate in a reverse direction to
that corresponding to generator action.

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19. If the input of 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) power factor of the load remains constant
(D) power factor of the load changes from lagging to leading.

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20. For 50 Hz system the maximum speed of an alternator can be
(A) approximately 3600 rpm
(B) approximately 3000 rpm
(C) 3600 rpm
(D) 3000 rpm.

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21. Voltage characteristic of an alternator is shown in figure. Which curve
represents the characteristics for leading power factor ?

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(A) A
(B) B
(C) C
(D) D.

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22. In the above figure, the characteristic for unity power factor is
represented by the curve maked
(A) A
(B) B
(C)C
(D )D.

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Questions 23 to 26 refer to the following data:

In a 50 kVA, star connected 440 V, 4-phase 50 Hz alternator, the effective
armature resistance is 0.25 ohm per phase. The synchronous reactance is
3.2 ohm per phase and leakage reactance is 0.5 ohm per phase.

23. Full load output current at unity power factor will be
(A) 65.6 A
(B) 55.4 A
(C) 45.6 A
(D) 35.4 A.

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24. Full load line voltage will be
(A) 500 V
(B) 471 V
(C) 450 V
(D) 435 V.

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25. No load line voltage will be
(A) 600 V
(B) 599 V
(C)592V
(D) 580 V.

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26. Percentage regulation of the alternator is approximately
(A) 55%
(B) 45%
(C) 35%
(D) 25%.

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27. In order that two alternators be put in parallel, which of the following
factors should be identical for both ?
(A) Voltage
(B) Frequency
(C) Phase sequence
(D) All of the above.

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28. When two alternators are running in parallel, their RKVA load share is
changed by changing their ................ while their kW load share is changed
by changing their ..............
(A) excitation, driving torque
(B) driving torque, excitation
(C) excitation, excitation
(D) driving torque, driving torque.

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29. Two-alternators are running in parallel. If the driving force of both the
alternators is changed, this will result in change is
(A) frequency
(B) back emf
(C) generated voltage
(D) all of the above.

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30. A three phase alternator has a phase sequence of RYB for its three
output voltages. In case the field current is reversed, the phase sequence
will become
(A) RBY
(B) RYB
(C) YRB

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31. The armature reaction of an alternator influences
(A) windage losses
(B) operting speed
(C) generated voltage per phase
(D) waveform of voltage generated.

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32. For the same power rating, a lower voltage alternator will be
(A) more efficient
(B) larger in size
(C) operating at high rpm
(D) more costly.

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33. An alternator is supplying 10A to an inductive load at 220 V, while
running at 1000 rpm. Now if the speed of the alternator is reduced to 750
rpm but the field current remains unchanged, the load current will become
(A) 18 A
(B) 13.3 A
(C) 10 A
(D) 7.5 A.

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34. Dampers in a large generator
(A) increase stability
(B) reduce voltage fluctuations
(C) reduce frequency fluctuations.

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35. An alternator is rated for 75 kW at 0.8 power factor. It means that
(A) alternator has 4 poles
(B) alternator can supply 75 kW at 0.8 power factor
(C) alternator can supply power only to loads having power factor 0.8 only
(D) the peak efficiency of alternator occurs only at 75 kW load having 0.8
lagging power factor.

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36. The regulation of an alternator is
(A) the reduction in terminal voltage when alternator is loaded
(B) the variation of terminal voltage under the conditions of maximum and
minimum excitation
(C) the increase in terminal voltage when load is thrown off
(D) the change in terminal voltage from lagging power factor to leading
power factor.

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37. A magnetisation curve represents the relationship between
(A) reactive and non-reactive components of voltage
(B) exciting currents and terminal voltage
(C) power factor and terminal voltage
(D) magnetic flux and armature current.

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38. In an alternator if the armature reaction produces demagnetisation of
the main field, the power factor should be
(A) Zero, lagging load
(B) Zero, leading load
(C) Unity.

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39. In an alternator if the armature reaction produces magnetisation of the
main field the power factor should be
(A) Zero, lagging load
(B) Zero, leading load
(C) Unity.

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40. When an alternator is supplying unity power factor load, the armature
reaction will produce
(A) magnetisation of the main field
(B) demagnetisation of the main field
(C) distortion of the main field.

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41. An alternator has full load regulation of 4% when the power factor of the
load is 0.8 lagging while alternator runs at 1500 rpm. The full load
regulation of 1400 rpm for 0.8 pf lagging load will be
(A) 15/14 x 4 percent
(B) 14/15 x 4 percent
(C) 4 percent
(D) Depends on other factors also.

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42. The Potier's triangle separates the
(A) iron losses and copper losses
(B) field mmf and armature mmf
(C) stator voltage and rotor voltage
(D) armature leakage reactance and armature reaction mmf.

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43. In the Potier's triangle, the Potier reactance drop per phase is 22 volts
per phase at 88 amperes per phase. The Potier's reactance per phase is
(A) 0.22
(B) 0.25
(C) 0.30
(D) 0.44.

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44. Two alternators are running in parallel. The excitation of one of the
alternator is increased. The result will be
(A) machine with excess excitation will burn
(B) both machines will start vibrating
(C) power output will decrease
(D) wattless component will change.

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45. The power output of an alternators is 100 kW. In order that the tangent
of pf angle may be 0.8 lagging, the KVAR rating must be
(A) 80 cos KVAR
(B) 80 sin KVAR
(C) 80 KVAR
(D) -80 KVAR.

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46. The power output of an alternator is 40 kW and KVAR component is -
25. What will be the value of tan ( being the power factor angle) ?
(A) 0.625 lagging
(B) 0.625 leading
(C) 0.375 lagging
(D) 0.375 leading.

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47. When short pitch coils of 160 are used in an alternator, which harmonic
component will not be present in the output emf ?
(A) third
(B) fifth
(C) seventh
(D) ninth.

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48. A 120 MW turbo alternator is supplying power to 80 MW load at p.f.
lagging. Suddenly the steam supply to the turbine is cut off and the
alternator remains connected to the supply network and the field supply
also remains on. What will happen to the alternator ?
(A) The stator winding of the alternator will get burnt
(B) The rotor winding of the alternator will get burnt
(C) The alternator will continue to run as a synchronous motor rotating in
the same direction
(D) The alternator will continue to run as a synchronous motor rotating in
the opposite direction.

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49. The figure shows the characteristics of an alternator. Which curve
represents synchronous impedance ?

(A) curve A
(B) curve B
(C) curve C
(D) curve D.

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50. In the above figure (Figure of Question 49) which curve represents
short circuit ?
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(A) curve A
(B) curve B
(C) curve C
(D) curve D.

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51. In the above figure which curve represents open circuit voltage ?
(A) curve A
(B) curve B
(C) curve C
(D) curve D.

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52. For a peripheral speed of 314 m/s, a 2 pole cylindrical machine will
have maximum diameter of
(A) 255 cm
(B) 235 cm
(C) 200 cm
(D) 170 cm.

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53. The rotor of the salient pole alternator has 24 poles. The number of
cycles of emf in one revolution would be
(A) 24
(B) 12
(C) 6
(D) 4.

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54. Two alternators A and B are sharing an inductive load equally. If the
excitation of alternator A is increased
(A) alternator B will deliver more current and alternator A will deliver less
current
(B) alternator B will deliver less current and alternator A will deliver more
current
(C) both will continue to share load equally
(D) both will deliver more current.

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55. Desirable feature for the parallel operation of two alternators is
(A) both should have same resistance
(B) both should have same reactance
(C) both should have less of resistance as compared to synchronous
reactance
(D) both should have more of resistance as compared to synchronous
reactance.

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56. Alternators used in aircraft systems usually have frequency of
(A) 25 Hz
(B) 50 Hz
(C) 100 Hz
(D) 400 Hz.

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57. High frequency on aircraft alternators is selected in order to
(A) free the systems from external disturbance
(B) compensate for high speeds
(C) compensate for high altitudes
(D) reduce the bulk.

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58. A 20 pole ac generator rotates at 600 rpm. The periodic time of current
in seconds per cycle is
(A) 0.009
(B) 0.004
(C) 0.008
(D) 0.01.

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59. What kind of rotor is most suitable for turbo alternators ?
(A) salient pole type
(B) non-salient pole type
(C) both (A) and (B) above

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60. The synchronizing power developed in one of the alternators, when two
alternators are running in parallel, will load the same alternator in which it is
developed and reduce its speed
(A) True
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(B) False

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61. If the input to the prime mover of an alternator is kept constant but the
excitation is changed then the
(A) reactive component of the output is changed
(B) active component of the output is changed
(C) power factor of load remains constant.

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62. If two machines are running in synchronism and the voltage of one
machine is suddenly increased
(A) the machines will burn
(B) both machines will stop
(C) synchronising torque will be produced to restore further synchronism.

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63. In an alternator, at 0.8 lagging power factor, the generated voltage per
phase is 240 V to give a rated terminated voltage ' V '. If the power factor of
load increases to unity, the generated voltage per phase must be
(A) 260 V
(B) 250 V
(C) 240 V
(D) 225 V.

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64. The advantage of salient poles in an alternator is
(A) reduce noise
(B) reduced windage loss
(C) adoptability to low and medium speed operation
(D) reduce bearing loads and noise.

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65. Magnetisation curves for no load and full load unity power factor are
shown in figure below. Which is the magnetisation curve for full load 0.8
power factor ?

(A) curve A
(B) curve B
(C) curve C
(D) curve D.

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66. At a particular instant a turbo alternator is generating 80 MW at 0.8
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power factor lagging. Now if the steam supply valve to the steam turbine is
further opened and the excitation is not changed
(A) the speed of the alternator will increase but kW delivered will remain
unchanged
(B) the speed of the alternator will increase and kW delivered will also
increase
(C) the speed of the alternator will remain unchanged but it can meet more
kW demand
(D) the speed of the alternator will remain unchanged but it will deliver more
kVA.

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67. Two alternators A and B are sharing a resistive load (p.f. = 1 ) equally.
Now if the excitation of alternator A is increased
(A) alternator A will become lagging and alternator B will become leading
(B) alternator A will become leading and alternator B will become lagging
(C) both alternators will continue to operate on unity power factor
(D) both alternators will operate on lagging power factor
(E) both alternators will operate on leading power factor.

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68. The advantage of providing damper winding in alternators is
(A) elimination of harmonic effects
(B) provide a low resistance path for the currents due to unbalancing of
voltage
(C) oscillations are provided when two alternators operate in parallel

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69. When two alternators are running in exactly synchronism, the
synchronising power wil be
(A) zero
(B) sum of the output of two
(C) unity
(D) 0.707.

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Questions 70 to 72 refer to the figure given below :

70. Load characteristic curves for an alternator are shown. The curves are
drawn for 0.8 pf lagging, 0.8 p.f. leading, 0.7 p.f. leading and 0.9 p.f.
lagging. Which curve represents the characteristics for 0.8 p.f. leading ?
(A) curve A
(B) curve B
(C) curve C
(D) curve D.

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71. Which curve represents the data for 0.8 p.f. lagging ?
(A) curve A
(B) curve B
(C) curve C
(D) curve D.

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72. Which curve represents the data for 0.9 p.f. lagging ?
(A) curve A
(B) curve B
(C) curve C
(D) curve D.

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73. The balanced short circuit current of a three phase alternator is 25
amperes at 1500 rpm. For the same field current, the balanced short
current at 1400 rpm will be
(A)18 A
(B) 27 A
(C) 20 A
(D) 20*(2)
1/2
A
2 of 3

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74. A three phase alternator has a phase sequence of RYB for its three
output voltages, for clockwise rotation. Now if the alternator is rotated
anticlockwise, the phase sequence will be
(A) RYB
(B) RBY
(C) BYR

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75. In a synchronous machine, if the field flux axis is ahead of the armature
field axis, in the direction of rotation, the machine working as
(A) asynchronous motor
(B) asynchronous generator
(C) synchronous motor
(D) synchronous generator.

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76. In synchronous alternator, which of the following coils will have emf
closer to sine waveform ?
(A) concentrated winding in full pitch coils
(B) concentrated winding in short pitch coils
(C) distributed winding in full pitch coils
(D) distributed winding in short pitch coils.

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77. An alternator has rated field current of 4 A. The alternator develops 180
V while drawing a field current of 2 A at 750 rpm. If the field current is made
4 A at 750 rpm generated voltage could be
(A) 400 V
(B) 380 V
(C) 60V
(D) 330 V.

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78. The armature reaction of an alternator will be completely magnetizing in
case the load power factor is
(A) unity
(B) 0.707
(C) zero lagging
(D) zero loading.

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79. Which of the following is not an integral part of synchronous generator
system ?
(A) prime mover
(B) distribution transformer
(C) excitation system
(D) protection system.

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80. For turbo generators the range of excitation voltage is
(A) 10 to 20 V
(B) 30 to 100 V
(C) 100 to 800 V
(D) 1000 to 1800 V.

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81. In case of low speed hydrogenerators, the short circuit ratio is usually
(A) 0.1 to 0.5
(B) 0.5 to 0.6
(C) 0.6 to 1.0
(D) 1.0 to 1.5.

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82. The permissible duration for which a generator of rated frequency 50
Hz can run at 46 Hz is
(A) zero
(B) one cycle
(C) one second
(D) one minute.

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83. The permissible duration in supply . frequency is
(A) 2 %
(B) 5 %
(C) 10 %
(D) 25 %.

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84. The regulation of an alternator is likely to be negative in case of
(A) high speed alternators
(B) slow speed alternators
(C) lagging power factor of the load
(D) leading power factor of the load.

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Questions 85 to 88 refer to the data given below:

A phase, 50 Hz, 6600 V, alternator is rated at 6600 kW at 0.8 power factor
and a full load efficiency of 90%.

85. kVA is rating of the alternator is
(A) 750 kVA
(B) 7500 kVA
(C) 75000 kVA
(D) 750000 kVA.

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86. The current rating of the alternator is
(A) 65.63 A
(B) 656.3 A
(C) 6563 A
(D) 65630 A.

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87. The input to the alternator is
(A) 666.6 kW
(B) 6666 kW
(C) 66660 kW
(D) 666,600 kW.

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88. If the input. to an alternator remains unaltered, but excitation is changed
then which of the following will not change ?
(A) kVA output
(B) kW output
(C) power factor

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89. Which of the following method is likely to give the voltage regulation
more than the actual value ?
(A) Synchronous reactance method
(B) MMF method
(C) Zero power factor method

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90. The effect of cross magnetization in an alternator field is to make the
output
(A) true sinusoidal
(B) non-sinusoidal
(C) harmonic free

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Synchronous
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91. In order to reduce the harmonics in the emf generated in an alternator
(A) slots are skewed
(B) salient pole tips are chamfered
(C) winding is well distributed

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92. The maximum power in a synchronous machine is obtained when the
load angle is
(A) 0
(B) 85
(C) 120
(D) 135.

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93. The emf generated due to nth harmonic component of flux in an
alternator will be
(A) n times the fundamental emf
(B) same as fundamental emf
(C) less than the value of fundamental emf.

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94. Synchronizing torque comes into operation under all of the following
cases EXCEPT
(A) phase difference between two voltages
(B) frequency difference between two voltages
(C) voltage difference between two voltages
(D) reduction in exciting current in one of the alternators.

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95. Unbalanced 3-phase stator currents cause
(A) double frequency currents in the rotor
(B) healing of rotor
(C) vibrations

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96. In large generators protection provided against external faults is
(A) biased differential protection
(B) sensitive earth fault protection
(C) inter-turn fault protection

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97. Pitch factor is the ratio of the emfs of
(A) short pitch coil to full pitch coil
(B) full pitch winding to concentrated winding
(C) full pitch winding to short pitch winding
(D) distributed winding to full pitch winding.

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98. In an alternator if the winding is short pitched by 50 electrical degrees,
its pitch factor will be
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(A) 1.0
(B) 0.866
(C) 0.75
(D) 0.50.

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99. The Potier's triangle separates
(A) stator losses and rotor losses
(B) fixed losses and variable losses
(C) armature voltage and field voltage
(D) armature leakage reactance and armature reaction mmf.

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100. If a single phase alternator has 8 slots per pole uniformly speed, but
the winding is arranged with the middle two left empty, the breadth
coefficient will be
(A) 0.99
(B) 0.88
(C) 0.67
(D) 0.53.

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101. Two alternators are running in parallel. If the field of one of the
alternator is adjusted, it will
(A) reduce its speed
(B) change its load
(C) change its power factor
(D) change its frequency.

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102. A generator is operating by itself supplying the system loads. The
reactive power supplied by the generator will
(A) depend on prime mover rpm
(B) depend on type of insulation used
(C) depend on the amount demanded by the load
(D) depend on inter-coil inductance.

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103. Which of the following part plays important role in over speed
protection of a generator ?
(A) Over current relay
(B) Alarm
(C) Differential protection
(D) Governor.

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104. Which type of protection is provided on a generator to protect against
stator insulation failure ?
(A) Differential protection
(B) Thermocouple actuated alarm
(C) Over current relay
(D) Reverse power relay.

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105. Which relays comes into operation in the event of the failure of prime
mover connected to ihe generator ?
(A) Reverse power relay
(B) Differential relay
(C) Buchholz relay

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106. In alternators, the distribution factor is defined as the ratio of emfs of
(A) distributed winding to connected winding
(B) full pitch winding to distributed winding
(C) distributed winding to full pitch winding
(D) concentrated winding to distributed winding.

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107. One of the advantages of distributing the winding in alternator is to
(A) reduce noise
(B) save on copper
(C) improve voltage waveform
(D) reduce harmonics.

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108. In case of a uniformly distributed winding, the value of distribution
factor is
(A) 0.995
(B) 0.80
(C) 0.75
(D) 0.50.

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109. The advantage of a short pitch winding is
(A) low noise
(B) increased inductance
(C) suppression of harmonics
(D) reduced eddy currents.

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110. Two alternators are connected in parallel. Their kVA and kW load
share can be changed by changing respectively their
(A) driving torque and excitation
(B) excitation and driving torque
(C) excitations only
(D) driving torques only.

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111. In case of alternators, the dark and bright lamp method is used for
(A) phase sequence
(B) load balancing
(C) synchronizing
(D) load transfer.

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112. The advantage of using short pitched windings in an alternator is that
it
(A) suppresses the harmonics in generated emf
(B) reduces the total voltage around the armature coils
(C) saves copper used in windings
(D) improves cooling by better circulation of air.

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113. For the same power rating, an alternator operating at lower voltage will
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be
(A) less noisy
(B) costlier
(C) larger in size
(D) more efficient.

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114. Which of the following is the common synchronous speed in rpm
between 60 Hz and 50 Hz alternators ?
(A) 900
(B) 600
(C) 375
(D) 225.

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115. All of the following losses for a synchronous machine are fixed
EXCEPT
(A) Bearing friction loss
(B) Copper loss
(C) Windage loss
(D) Core loss.

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116. Salient pole type rotors as compared to cylindrical pole type are
(A) smaller in diameter and larger in axial length
(B) larger in diameter and smaller in axial length
(C) larger in diameter as well as axial length
(D) small in diameter as well as axial length.

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117. In a synchronous machine, the field flux axis is ahead of the armature
field axis in the direction of rotation, the machine is working as
(A) asynchronous alternator
(B) asynchronous motor
(C) synchronous motor
(D) synchronous alternator.

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118. Which of the following is not a common synchronous speed in rpm
between a 50 Hz and 25 Hz alternator ?
(A) 750
(B) 375
(C) 250
(D) 200.

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119. The effective voltage in one phase of an alternator having 240 turns
per phase, frequency of 60 Hz and flux per pole of 2.08 x 10
6
lines will be
(A) 332.5 V
(B) 665 V
(C) 1330 V
(D) 2660 V.

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120. The maximum current that can be supplied by an alternator depends
on
(A) speed of the exciter
(B) number of poles
(C) exciter current
(D) strength of the magnetic field.

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Synchronous
Generator Theory
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121. The windings for an alternator are
I. 36 slots, four poles, span 1 to 8
II. 72 slots, six poles, span 1 to 10
III. 96 slots, six poles, span 1 to 12.
The windings having pitch factors of more than 0.9 are
(A) I and II only
(B) II and III only
(C) I and II only
(D) I, II and III.

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Questions 122 to 124 refer to data given below:

A 500 kVA ,2300 volt three phase star connected alternator has a full load
armature-resistance drop per phase of 50 volts and a combined armature
reactance plus armature-reaction drop of 500 volts per phase

122. The percent regulation of the alternator at unity power factor is
(A) 1.05
(B) 10.5
(C) 21.5
(D) 27.5.

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123. The percent regulation of the alternator at 0.866 power factor lagging
is
(A) 26.3
(B) 20.1
(C) 16.6
(D) 10.5.

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124. The percent regulation of the alternator at 0.8 power factor leading is
(A) 13.2
(B) 26.4
(C) - 26.4
(D) - 13.2.

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125. The imaginary or fictitious part of synchronous reactance takes care of
(A) armature reaction
(B) voltage regulation
(C) inductive reactance

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126. In an alternator, the use of short pitch coils of 160 will indicate the
absence of
(A) third harmonic
(B) fifth harmonic
(C) seventh harmonic
(D) ninth harmonic.

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127. When a generator designed for operation at 60 Hz is operated at 50
Hz
(A) operating voltage must be derated to (50/60) of its original value
(B) operating voltage must be derated to (50/60)
2
of its original value
(C) kVA rating can be upgraded to (60/50) of the rated value
(D) the generator will not take any load.

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128. Overheating of generator's winding
(A) reduces generated voltage
(B) reduces power factor
(C) reduces life of the machine
(D) does not have any significant effect.

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129. Rotor shaft of 500 MW alternator is supported in
(A) ball bearings
(B) roller bearings
(C) needle bearings
(D) journal bearings.

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130. The voltage of field system for an alternator is usually
(A) less than 200 V
(B) between 200 V and 440 V
(C) 400 V
(D) more than 1 kV.

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131. Maximum electric power output of a synchronous generator is
(A) Xs / VtEf
(B) V
2
t / Xs
(C) E
2
f / Xs
(D) VtEf / Xs

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132. The electrical angle between the field axis and axis of armature
reaction of a loaded synchronous generator with armature current lagging
behind the excitation emf by is
(A) - 90
(B) + 90
(C) 90 -
(D) + 180.

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133. Two synchronous generators G1and G2 are equally sharing the KVAR
of the load while operating in parallel. Keeping the terminal voltage fixed in
order to shift part of the KVAR load from G2 to G1
(A) The field current of G1 is lowered
(B) The field current of G2 is raised
(C) The field current of G1 is raised and of G2 lowered
(D) The field current of G1 is lowered and of G2 is raised.

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134. A synchronous generator is operating with excitation adjusted for unity
power factor current at constant load. When on increasing the excitation
the power factor
(A) will lag
(B) will lead
(C) will become zero

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135. On changing the speed of an alternator from 4000 rpm to 2000 rpm,
the generated emf phase will become
(A) 1/4
(B) 1/2
(C)1/3
(D)1/5

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Synchronous
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136. Zero power factor method of an alternator is used to find its
(A) field resistance
(B) armature resistance
(B) armature resistance
(C) efficiency
(D) voltage regulation.

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137. The power factor of an alternator is obtained from its
(A) excitation
(B) speed
(C) load

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138. For parallel operation, alternators must have
(A) same speed
(B) same kVA rating
(C) same voltage rating

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139. For alternation having fractional pitch of 5/6 the coil span is
(A)90
(B)120
(C)150
(D)180

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140. Fractional pitch to eliminate 7th harmonic from alternator emf is
(A) 7/6
(B) 6/7
(C) 6/5
(D) 3/5.

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141. Consider the following statements about a three-phase synchronous
generator synchronized to an infinite bus when its mechanical input is
increased gradually with field current held constant:
1. The power factor of the current supplied becomes more lagging.
2. The power factor of the current supplied improves.
3. The power factor remains unity.
4. The load angle is increased.
Of these statements
(A) 1 alone is correct
(B) 2 alone is correct
(C) 2 and 4 are correct
(D) 3 and 4 are correct.

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142. A 3-phase synchronous generator, with its armature resistance and
the leakage reactance being neglected, is synchronized to an infinite bus
and its field excitation is kept constant thereafter. Now the machine is
loaded by Supplying mechanical input to the shaft so that the load-angle
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reaches a value of 60 Under this condition, the operating power-factor
would be
(A) 0.866 leading
(B) 0.866 lagging
(C) 0.5 leading
(D) 0.5 lagging.

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143. A round rotor synchronous generator has a leakage reactance of 10%,
armature reaction reactance of 90% and negligible armature resistance.
With the machine initially running at rated speed and terminal voltage of 1.0
p.u., a 3-phase short-circuit is applied. The sustained armature current will
be
(A) 1.25 p.u.
(B) 1.11 p.u.
(C) 1.0 p.u.
(D) 0.9 p.u.

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144. Following a sudden short-circuit at the terminals of a 3-phase
unloaded synchronous generator, the initial effect of the pole-face damper
windings, is to
(A) establish the armature flux through the direct-axis magnetic circuit of the
machine
(B) allow only partial linkage of the armature flux with the main field winding
(C) confine the armature flux to completely link the damper winding
(D) repel the armature flux and confine it to the leakage flux path in the
air-gap.

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145. In a synchronous generator operating at zero pf lagging, the effect of
armature reaction is
(A) magnetizing
(B) demagnetizing
(C) cross-magnetizing
(D) both magnetizing and cross-magnetizing.

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146. Which of the following limit the reactive power output of a synchronous
generator ?
1. Armature current
2. Field current
3. Load angle
4. Prime mover input.
Select the correct answer using the codes given below:
Codes
(A) land 2
(B) 2 and 3
(C) 3 and 4
(D) land 4.

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147. The steady-state stability limit of a synchronous generator can be
increased by
(A) an increase in its reactance
(B) an increase in the excitation of the machine
(C) a decrease in the moment of inertia of the machine
(D) an increase in the moment of intertia of the machine.

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