Synchronous Motor MCQ

91. A three-phase synchronous generator is connected to an infinite bus. If the excitation of the generator fails then it acts as a

1. Synchronous motor
2. Induction motor
3. Induction generator
4. None of the other options

92. What type of excitation is given to the rotor winding of a synchronous motor?

1. DC supply at 100-250V
2. AC supply at 400 V
3. Revolving field
4. Induction from stator current

93. Maximum power developed in a synchronous motor occurs at a coupling angle of?

1. 120°
2. 60°
3. 90°
4. 0°

94. A synchronous motor is said to be ‘floating’ when it operates

1. On no load and without loss
2. On constantly varying load
3. On pulsating load
4. On high load & variable supply voltage

95. An unexcited single-phase synchronous motor is

1. Reluctance motor
2. Repulsion motor
3. Universal motor
4. A.C. series motor

96. In case the field of a synchronous motor is under excited, the power factor will be

1. Leading
2. Lagging
3. Zero
4. Unity

97. Synchronous motor can operate at

1. Lagging power factor only
2. Leading power factor only
3. Unity power factor only
4. Lagging, leading & unity power factor

98. Overexcited synchronous motors are used for

1. improving power factor of power systems with more inductive load
2. reducing the copper losses of inductive load
3. reducing power factor of power systems with more inductive load
4. maintaining the power factor to zero

99. The machine used for power factor correction is

1. Induction generator
2. Universal motor
3. Stepper motor
4. Synchronous motor

100. When overexcited, synchronous motor has

1. Leading power factor
2. Zero power factor
3. Unity power factor
4. Lagging power factor

101. In a synchronous motor, the rotor copper losses are met by

1. Supply mains
2. Armature
3. Motor input
4. DC source

102. V-curves for isolated, 3-phase synchronous motor show

1. the variation of mechanical power with field excitation at constant speed
2. the variation of armature voltage with field excitation at constant mechanical power
3. the variation of armature voltage with mechanical power at constant field excitation
4. the variation of armature current with field excitation at constant mechanical power

103. Which one of the following is correct?

1. Synchronous motor is supplied with d.c. voltage in the armature winding
2. Synchronous motor is supplied with ac voltage in the field winding
3. Synchronous motor is supplied with rectified voltage in the armature winding
4. Synchronous motor is supplied with d.c. voltage in the field winding

104. Damping winding in a synchronous motor

1. improves power factor of the motor
2. increase hunting of the motor
3. reduces windage losses
4. increases starting torque

105. A synchronous motor connected to an infinite busbar is driving a load corresponding to its rated capacity, with a torque angle of 30°. If the load is increased to $\sqrt{3}$ times the rated load, what is the corresponding torque angle?

1. 30°
2. 45°
3. 60°
4. 15°