MCQs on Synchronous Motor
1. Synchronous motors generally have
- salient pole rotor
- smooth cylindrical rotor
- either the salient pole rotor or smooth cylindrical rotor
- none of the above
2. Number of slip rings in a 3-phase synchronous motor will be
- 0
- 1
- 2
- 3 or 4
3. Electromgnetic torque or force developed in any physical system tends to
- increase both the field energy and co-energy at constant current
- reduce both the field energy and co-energy at constant current
- reduce reluctance
- reduce inductance
- both (1) and (3)
4. An ideal synchronous motor has no starting torque because the
- rotor is made up of salient poles
- relative velocity between the stator and rotor mmfs is zero
- relative velocity between the stator and rotor mmfs is not zero
- rotor winding is highly reactive
5. In a synchronous motor
- the rotor mmf and stator mmf are stationary with respect to each other
- rotor mmf rotates slightly faster in comparison to stator mmf
- stator mmf rotates slightly faster than rotor mmf
- none of the above
6. A synchronous machine is revolving armature and stationary field type. Under steady-state conditions, the air gap field
- rotates at synchronous speed with respect to stator
- rotates at synchronous speed in the direction of rotation of rotor
- remains stationary with respect to stator
- remains stationary with respect to rotor
7. In a synchronous machine, if the armature field axis is ahead of the field flux axis in the direction of rotation, the machine operating is
- synchronous motor
- synchronous generator
- asynchronous motor
- asynchronous generator
8. In a synchronous machine, if the axis of the field flux coincides with that of armature flux, the machine
- will operate smoothly without any vibration
- is said to be floating
- is operating as a synchronous generator
- is operating as a synchronous motor.
9. In a 3-phase synchronous motor, the magnitude of field flux
- remains constant at all loads
- varies with load
- varies with speed
- varies with power factor
10. What is the angle between the induced voltage and supply voltage of a synchronous motor under running condition?
- Zero
- Greater than zero but ≤ 90°
- Between 90° and 180°
- > 180