Synchronous Motor MCQ

61. The ratio of starting torque to running torque in a synchronous motor is

1. 0
2. 1
3. 2
4. 4

62. The angle between rotating stator flux and rotor poles is called

1. torque angle
2. obtuse angle
3. synchronizing angle
4. power factor angle

63. Hunting in a synchronous motor takes place when

1. supply voltage fluctuates
2. load varies
3. power factor is unity
4. motor is underloaded

64. A three-phase synchronous motor will have

1. no slip rings
2. one slip ring
3. two slip rings
4. three slip rings

65. For very low speed and high power applications, the best-suited ac motor is

1. Slip-ring induction motor
2. Squirrel cage induction motor
3. AC commutator motor
4. Synchronous motor

66. A salient pole synchronous motor is running at no load. Its excitation is reduced to zero

1. It will stop
2. It will remain running at synchronous speed
3. It will loose synchronism
4. It is uncertain

67. Embedding the damper winding in the pole face serves which of the following purposes?

1. Eliminate hunting and provide adequate starting torque
2. Reduce windage losses
3. Eliminate losses on account of air friction
4. Reduce bearing friction

68. For the following specifications of a synchronous motor determine the ratio of no-load speed to full load speed.

1. 1:1
2. 2:3
3. 2:7
4. 3:5

69. On which of the following does the back emf set up in the stator of a synchronous motor depend.

1. Rotor speed
2. Rotor excitation
3. coupling angle

Choose the correct answer from the options given below.

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

70. Which of the following leads to reduction in the size of a synchronous motor?

1. Increase in horsepower rating
2. Decrease in load angle
3. Increase in flux density
4. Decrease in flux density

71. It will be the effect on a salient pole synchronous motor if its field current is switched off (provided the motor runs at no load)?

1. It will stop
2. It continues to run at synchronous speed
3. It continues to run at a speed slightly more than the synchronous speed
4. It continues to run at a speed slightly less than the synchronous speed

72. When a synchronous motor is _______ it operates with leading power factor current.

1. under-excited
2. critically excited
3. over-excited
4. heavily loaded

73. By reversing __________, the direction of rotation of a synchronous motor can be reversed.

1. supply phase sequence
2. current to the field winding
3. polarity of rotor poles
4. either ‘polarity of rotor poles’ or ‘supply phase sequence’.

74. A synchronous motor is found more economical over a load of

1. 2 kW
2. 20 kW
3. 50 kW
4. 100 kW

75. Which of the following motors is preferred as a drive, when quick speed reversal is the main consideration?

1. Wound rotor induction motor
2. Synchronous motor
3. Squirrel case induction motor
4. DC Motor