The V-curve of a synchronous motor shifts upward with

 

51. The armature current in a synchronous motor lags the terminal voltage when the motor is
    A) Over-excited
    B) Under-excited
    C) At unity excitation
    D) None

B

52. The armature current in a synchronous motor leads the terminal voltage when the motor is
    A) Under-excited
    B) Over-excited
    C) Normally excited
    D) None

B

53. The power developed in a synchronous motor is proportional to
    A) Sine of load angle
    B) Cosine of load angle
    C) Tangent of load angle
    D) Square of load angle

A

54. The mechanical output of a synchronous motor is maximum when the torque angle is
    A) 0°
    B) 45°
    C) 90°
    D) 180°

C

55. The synchronous impedance is given by
    A) √(Ra² + Xs²)
    B) Ra + Xs
    C) Ra / Xs
    D) Ra – Xs

A

56. If field excitation of a synchronous motor fails, the motor will
    A) Stop immediately
    B) Continue to run as induction motor
    C) Run at reduced speed
    D) Run at higher speed

B

57. The load angle in a synchronous motor is usually less than
    A) 10°
    B) 45°
    C) 90°
    D) 180°

C

58. When the load angle of a synchronous motor increases, the developed torque
    A) Decreases
    B) Increases
    C) Remains constant
    D) Becomes zero

B

59. The maximum torque that a synchronous motor can develop without losing synchronism is called
    A) Starting torque
    B) Pull-out torque
    C) Breakdown torque
    D) Pull-in torque

B

60. A synchronous motor is said to be over-excited when
    A) Field current is less than normal
    B) Field current is more than normal
    C) Field current is zero
    D) Field current is normal

B

61. When a synchronous motor runs at constant load and excitation is increased, its power factor
    A) Increases
    B) Decreases
    C) Remains constant
    D) Becomes unity

B

62. The starting current of a synchronous motor is
    A) Very high
    B) Zero
    C) Normal
    D) Negligible

A

63. The armature reaction effect in synchronous motor depends on
    A) Armature current
    B) Field current
    C) Load
    D) Both A and C

D

64. The back emf in a synchronous motor is
    A) In phase with supply voltage
    B) Opposes the supply voltage
    C) Leads the supply voltage
    D) Lags the supply voltage

B

65. The effect of increasing field current on armature current is shown by
    A) Inverted V-curve
    B) V-curve
    C) Power curve
    D) Load curve

B

66. The excitation current required for unity power factor operation
    A) Is maximum
    B) Is minimum
    C) Is zero
    D) Depends on load

B

67. The current drawn by a synchronous motor at no-load is
    A) Small and lagging
    B) Large and leading
    C) Small and leading or lagging depending on excitation
    D) Zero

C

68. A synchronous motor running at synchronous speed can be converted into a generator by
    A) Increasing load
    B) Increasing excitation and driving it
    C) Decreasing voltage
    D) Decreasing excitation

B

69. The torque developed by a synchronous motor at constant excitation is proportional to
    A) sin(δ)
    B) cos(δ)
    C) tan(δ)
    D) δ

A

70. The synchronous reactance is the sum of
    A) Armature resistance and leakage reactance
    B) Leakage reactance and field reactance
    C) Armature reaction and leakage reactance
    D) Armature resistance and core loss

C

71. The phasor representing back emf in a synchronous motor
    A) Lags the armature current
    B) Leads the armature current
    C) Opposes the applied voltage
    D) Leads the supply voltage

C

72. For constant torque, if excitation is decreased, the power factor
    A) Becomes leading
    B) Becomes lagging
    C) Becomes unity
    D) Remains unchanged

B

73. For a given excitation, the torque of a synchronous motor increases with
    A) Increasing load angle
    B) Decreasing load angle
    C) Increasing speed
    D) Decreasing excitation

A

74. The armature current of a synchronous motor is minimum when it operates at
    A) Unity power factor
    B) Leading power factor
    C) Lagging power factor
    D) Zero power factor

A

75. The starting torque of a synchronous motor with damper winding is developed by
    A) Induction motor principle
    B) DC excitation
    C) Permanent magnet
    D) Field winding

A

76. The torque angle of a synchronous motor changes with
    A) Supply voltage
    B) Load
    C) Field current
    D) Power factor

B

77. The field system of a synchronous motor is excited by
    A) Separate DC source
    B) AC source
    C) Induced current
    D) None

A

78. The voltage regulation of a synchronous motor is
    A) Positive
    B) Negative
    C) Zero
    D) High

B

79. The speed of a synchronous motor can be changed by
    A) Changing supply frequency
    B) Changing supply voltage
    C) Changing load
    D) Changing excitation

A

80. The synchronous motor’s speed depends on
    A) Load torque
    B) Supply frequency and poles
    C) Supply voltage
    D) Power factor

B

81. The maximum torque developed by a synchronous motor is independent of
    A) Supply voltage
    B) Excitation
    C) Armature resistance
    D) Frequency

C

82. If excitation of a synchronous motor is increased beyond normal, the current
    A) Decreases and leads voltage
    B) Increases and lags voltage
    C) Decreases and lags voltage
    D) Remains same

A

83. Synchronous motor operating with lagging power factor is called
    A) Over-excited
    B) Under-excited
    C) Normally excited
    D) None

B

84. The angle between the rotating magnetic field and rotor poles is known as
    A) Torque angle
    B) Power angle
    C) Load angle
    D) All of the above

D

85. The torque of a synchronous motor at no-load is
    A) Maximum
    B) Minimum
    C) Zero
    D) Constant

C

86. The pull-in torque of a synchronous motor is
    A) Maximum torque developed during acceleration
    B) Torque to pull into synchronism
    C) Torque to start motor
    D) Zero torque condition

B

87. The V-curve of a synchronous motor shifts upward with
    A) Increased load
    B) Decreased load
    C) Decreased excitation
    D) Constant excitation

A

88. Synchronous motor can operate at any desired power factor by controlling
    A) Supply voltage
    B) Load
    C) Excitation
    D) Supply frequency

C

89. The stator current in a synchronous motor is determined by
    A) Supply voltage and excitation
    B) Speed
    C) Load only
    D) Frequency

A

90. The total torque on rotor in synchronous motor is
    A) Constant
    B) Varying periodically
    C) Zero
    D) Dependent on speed

A

91. The hunting can be minimized by
    A) Increasing load
    B) Using damper winding
    C) Decreasing excitation
    D) Increasing frequency

B

92. In synchronous motor, magnetic locking occurs between
    A) Stator and rotor poles
    B) Rotor and shaft
    C) Armature and field windings
    D) Stator coils

A

93. Synchronous motor is best suited for
    A) Variable load
    B) Constant load
    C) Rapid speed changes
    D) Frequent start-stops

B

94. The reactive power of an under-excited synchronous motor is
    A) Positive
    B) Negative
    C) Zero
    D) Infinite

A

95. The function of field current in synchronous motor is to control
    A) Power factor
    B) Speed
    C) Frequency
    D) Armature voltage

A

96. The stator current of a synchronous motor is lagging when
    A) Field excitation is low
    B) Field excitation is high
    C) Field excitation is normal
    D) None

A

97. The input power of a synchronous motor is equal to
    A) Output + losses
    B) Output – losses
    C) Rotor copper losses
    D) None

A

98. The synchronous motor consumes reactive power when
    A) Under-excited
    B) Over-excited
    C) At unity power factor
    D) None

A

99. The field current corresponding to unity power factor is called
    A) Critical excitation
    B) Normal excitation
    C) Maximum excitation
    D) Minimum excitation

A

100. The current drawn by an over-excited synchronous motor is
     A) Leading
     B) Lagging
     C) In phase
     D) Zero

A