Synchronous Motor MCQ

131. The term synchronous condenser refers to

1. A synchronous motor with a capacitor connected across the stator terminals to improve the power factor.
2. A synchronous motor operating at full-load with leading power factor.
3. An over-excited synchronous motor partially supplying mechanical load and also improving the power factor of the system to which it is connected.
4. An over-excited synchronous motor operating at no-load with leading power factor used in large power stations for improvement of power factor.

132. A 12-pole, 440 V, 50 Hz, 3-phase synchronous motor takes a line current of 100 A at 0.8 pf leading neglecting losses, the torque developed will be

1. 705 Nm
2. 1165 Nm
3. 1058 Nm
4. 525 Nm

133. The flux/pole in a synchronous motor with stator not connected to supply is Φ₁, and when connected to supply it is (3/4)Φ₁. The no-load current drawn from the supply under this condition would be

1. lagging the supply voltage
2. leading the supply voltage
3. in phase with the supply voltage
4. zero

134. A synchronous motor operates at rated voltage and frequency and has a load torque angle of 30°. If both the terminal voltage and frequency are reduced by 10%, then

1. the load torque angle remains the same
2. the load torque angle increases
3. the load torque angle decreases
4. nothing can be said about the torque angle

135. When the rotor speed in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop

1. induction motor torque
2. induction generator torque
3. synchronous motor torque
4. dc motor torque

136. In synchronous motor, ‘V’ curves represent the variation of

1. armature current with excitation (field).
2. armature current with maximum power developed
3. field excitation with stalling torque.
4. field excitation with minimum power developed.

137. In a synchronous machine the rotor speed becomes more than the synchronous speed during hunting, the damping bars develop

1. synchronous motor torque
2. dc motor torque
3. induction motor torque
4. induction generator torque

138. Consider the following statements regarding synchronous machines:

1. When a synchronous motor is over-excited, its back emf is greater than the supply voltage.
2. When a synchronous motor is over-excited, its power factor is leading.
3. Synchronous motor is used as capacitor where load is so large that construction of a static capacitor is impractical.

Which of these statements are correct?

1. i and iii only
2. i and ii only
3. i, ii and iii
4. ii and iii only

139. The maximum power delivered by 1500 kW, 3-phase, star-connected, 4 kV, 48 pole, 50 Hz synchronous motor, with synchronous reactance of 4 Ω per phase and unity power factor is

1. 4271.2 kW
2. 3505 kW
3. 1206.1 kW
4. 2078 kW

140. A 3-phase synchronous motor with constant excitation is driving a certain load drawing electric power from infinite bus at leading power factor. If the shaft load decreases

1. the power angle decreases while power factor increases
2. the power angle increases while power factor decreases.
3. both power angle and power factor increase.
4. both power angle and power factor decrease.