ONLINE Multiple Choice Questions EE- Synchronous Generator PAR 5


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 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
(D)
all
of the above.

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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)1/2A

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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
(D)
none of the above.

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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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