ONLINE Multiple Choice Questions EE-Synchronous Motors PART 7

91. In a synchronous machine in case the axis of
field flux is in line with the armature flux, then
(A)
the machine is working as synchronous motor
(B)
the machine is working as synchronous
generator
(C)
the machine is said to be floating
(D)
the machine will vibrate violently.

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92. If other factors remain constant, the speed
of a synchronous motor in its operating (and load) range is correctly described
by which of the following ?
(A)
The speed varies directly only in proportion
to the number of its poles
(B)
The speed is independent of the frequency of
the voltage supply
(C)
The speed depends on the frequency of the
voltage supply and the number of its poles
(D)
The speed depends on the magnitude of the
voltage supply and the number of
its poles.

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93. The induced emf in a synchronous motor
working on leading pf will be
(A) equal
to the supply voltage
(B) less
than the supply voltage
(C) more
than the supply voltage.

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94. A synchronous machine with low value of
short-circuit ratio has
(A) good speed regulation
(B) good
voltage regulation
(C) higher
stability limit
(D) lower
stability limit.

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95. While starting a synchronous motor by
induction motor action, very high emf is induced in the field. This induced emf
may damage the insulation of the field winding and of slip rings. The insulation
damage can φ be prevented by
(A) short-circuiting
the field winding by field discharge resistance
(B) splitting
the field winding into several sections
(C)
either of (A) or (B) above
(D) none
of the above.

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96. Synchronous motors, arc generally of
(A) induction
type machines
(B) cylindrical
pole type machines
(C) salient
pole type machines
(D) hysteresis
type machines.

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97. In which of the following motor the stator
and rotor magnetic fields rotate at the same speed
(A) Universal
motor
(B) Reluctance
motor
(C) Synchronous
motor
(D) Induction
motor.

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98. Higher the applied voltage ……………….. will be
the stator flux and ………………. will be the pull
in torque
(A) lower, greater
(B) greater, lower
(C) greater, greater
(D) lower, lower.

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Questions 99 to 101 refer
to data given below:

 
An industrial plant has a load of 1500 kVA at an average power factor of
0.6 lagging.

99. Neglecting all losses, the kVA input to a
synchronous condenser for an overall power factor of unity will be
(A) 300 kVA
(B)
400 kVA
(C) 600 kVA
(D) 1200 kVA.

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100. A
750 kVA synchronous condenser is used to correct the lagging power factor of
the plant. The total kVA of the plant is
(A) 503
(B) 10006
(C) 2012
(D) 4024.

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101. The
overall power factor is
(A) 0.895 lagging
(B) 0.75 lagging
(C) 0.75 leading
(D) unity.

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102. As
the load is applied on a synchronous motor, its speed does not fall. The load
is now supplied by
(A) decrease
in back emf
(B) change
in supply voltage
(C) the
stator magnetic field
(D) rotor
taking new angular position slightly back of its no load position.

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103. The
maximum power developed in a synchronous motor depends on all of the following
EXCEPT:
(A) Supply
voltage
(B) Direction
of rotation
(C) Rotor
excitation
(D) Maximum
value of coupling angle.

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104. In
a synchronous motor, on a fixed excitation when the load is doubled, the torque
angle φr will become
(A) 2 φr
(B) √2 φr
(C)φr/2
(D) φr/√2

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105. In
a synchronous motor, the armature current has the highest value when excitation
is
(A) zero
(B)
low
(C) high
(D) high and low.

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ONLINE Multiple Choice Questions EE-Synchronous Motors PART 8
ONLINE Multiple Choice Questions EE-Synchronous Motors PART 6

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