Synchronous Motor MCQ

31. If the type of excitation of synchronous motors is critical excitation then what will be the nature of power factors?

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

32. Find the stator winding voltage of a three-phase star-connected 5500V synchronous motor having synchronous reactance per phase of 20 Ω.

1. 3175.4 V
2. 5500 V
3. 3180 V
4. 9526 V

33. Which type of torque in synchronous motor is also called as break away torques?

1. Starting torque
2. Running torque
3. Pull torque
4. Pull-out torque

34. A synchronous motor operates as a synchronous condenser when it is

1. operated at unity power factor
2. under-excited
3. over-excited
4. connected in parallel with condensers

35. In a synchronous machine, if the field flux is ahead of the armature field axis, in the direction of rotation, the machine works as

1. asynchronous motor
2. asynchronous generator
3. synchronous motor
4. synchronous generator

36. A synchronous motor operated at no load with over-excitation condition to draw large leading reactive current and power is called a

1. Synchronous motor
2. Capacitor start motor
3. Synchronous condenser
4. None of the above

37. When 3-phase supply is given to the stator of the motor, a

1. rotating field is set up
2. pulsating field is set up
3. revolving field at synchronous speed is set up
4. rotating field at the rotor speed is set up

38. In a synchronous motor, the minimum armature current occurs at

1. zero power factor
2. unity power factor
3. lagging power factor
4. leading power factor

39. A synchronous motor is

1. Self-starting
2. Non-self-starting
3. Sometimes self-starting
4. None of them

40. ________ motor is a constant speed motor.

1. Synchronous motor
2. Schrage motor
3. Induction motor
4. Universal motor

41. In synchronous motor inverted V curve represents the relation between

1. field current and power factor
2. field current and armature current
3. armature current and power factor
4. none of these

42. Reduction in supply voltage by 10% will change the torque of an induction motor by

1. 19%
2. 38%
3. No change
4. 9.5%

43. Variation in dc excitation of a synchronous motor causes variation in

1. Speed of motor
2. Power factor
3. Armature current
4. Both armature current and power factor

44. When excitation of synchronous motor is increased up to normal excitation from under excitation, armature current

1. increases
2. decreases
3. remains constant
4. None of the above

45. Synchronous motors are to be used in situations where

1. The load is constant.
2. The load is required to be driven at very high speeds.
3. The load is to be driven at constant speed.
4. The starting torque requirement of the load is very high.