Synchronous Motor MCQ

121. The synchronous motor is

1. not a self-starting machine and does not run at synchronous speed
2. a self-starting machine and does not run at synchronous speed
3. not a self-starting machine and runs at synchronous speed
4. a self-starting machine and runs at synchronous speed

122. Hunting of a synchronous motor may be caused due to

1. Pulsating supply frequency & Varying load conditions
2. Neither pulsating supply frequency nor varying load conditions
3. Pulsating supply frequency
4. Varying load conditions

123. The unexcited single-phase synchronous motors are of

1. Neither reluctance nor hysteresis type
2. Reluctance type
3. Both reluctance and hysteresis type
4. Hysteresis type

124. The magnitude of armature current in synchronous motor operation

1. Has small value and leads for low excitation
2. Has large value and lags for low excitation
3. Has large value and leads for low excitation
4. Has small value and lags for low excitation

125. In a synchronous motor, the load angle and internal angle are denoted by α and θ respectively. The maximum torque or pull out torque of a synchronous motor occurs when

1. α + θ = 0°
2. α – θ = 90°
3. α + θ = 90°
4. α – θ = 0°

126. A synchronous compensator is a synchronous motor running

1. Without a mechanical load and variable excitation
2. Without a mechanical load and fixed excitation
3. With a mechanical load and fixed excitation
4. With a mechanical load and variable excitation

127. Which of the following motor is not self-starting?

1. Squirrel cage induction motor
2. Wound rotor induction motor
3. Synchronous motor
4. D.C. series motor

128. A 3-phase synchronous motor connected to AC mains is running at full load and unity power factor. If its shaft load is reduced to half, with field current held constant, its new power factor will be

1. lagging
2. leading
3. unity
4. dependent on machine parameters

129. From no-load to full-load, synchronous motors give

1. Constant speed
2. Variable speed
3. Gradually increasing speed
4. Gradually decreasing speed

130. Speed of synchronous motor on increasing load

1. becomes infinity
2. remains constant
3. increases
4. decreases