Most Synchronous Motors

71. The armature current of the synchronous motor has higher values for

1. high excitation only
2. low excitation only
3. both (a) and (b)
4. none of the above

View answer

72. The back e.m.f. in the stator of a synchronous motor depends on

1. number of poles
2. flux density
3. rotor speed
4. rotor excitation

View answer

73. The back e.m.f. of a synchronous motor depends on

1. speed
2. load
3. load angle
4. all of the above

View answer

74. The construction of a synchronous motor resembles

1. a series motor
2. an induction motor
3. an alternator
4. a rotary converter

View answer

75. The coupling angle or load angle of synchronous motor is defined as the angle between the

1. rotor and stator teeth
2. rotor and the stator poles of opposite polarity
3. rotor and the stator poles of the same polarity
4. none of the above

View answer

76. The duration of sudden snort-circuit test on a synchronous motor is usually about

1. one hour
2. one minute
3. one second
4. none of the above

View answer

77. The effect of increasing the load on a synchronous motor running with normal excitation is to

1. decrease both armature current and power factor
2. decrease armature current but increase power factor
3. increase armature current but decrease power factor
4. increase both its armature current and power factor

View answer

78. The efficiency of a properly designed synchronous motor will usually fall in range

1. 60 to 70%
2. 75 to 80%
3. 85 to 95%
4. 99 to 99.5%

View answer

79. The induced e.m.f. in a synchronous motor working on leading power factor will be

1. more than the supply voltage
2. less than the supply voltage
3. equal to the supply voltage
4. none of the above

View answer

80. The magnitude of field flux in a 3-phase synchronous motor

1. remains constant at all loads
2. varies with speed
3. varies with the load
4. varies with power factor

View answer