Alternator MCQ | Synchronous Generator MCQ

81. An alternator running at 3000 rpm generates voltage at 50 Hz. The number of poles of the alternator will be

1. 8
2. 6
3. 4
4. 2

82. Direction of the alternating e.m.f. produced in the stator conductors of an alternator is given by

1. Lenz’s law
2. Fleming’s left-hand rule
3. Fleming’s right-hand rule
4. Kirchoff’s Law

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

1. Synchronous motor torque
2. D.C. motor torque
3. Induction motor torque
4. Induction generator torque

84. We have assigned a frequency of 50 Hz to power system because it

1. can be easily obtained
2. gives the best result when used for operating both lights and machinery
3. easy calculations
4. none

85. Maximum speed of a synchronous machine for 50 Hz is

1. 1500 rpm
2. 3000 rpm
3. 20000 rpm
4. 30000 rpm

86. When a 3-phase alternator is suddenly short-circuited at its terminals, the initial value of short circuit current is limited by which one of the following?

1. Subtransient reactance
2. Transient reactance
3. Synchronous reactance
4. none

87. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycle per second will be

1. 120
2. 110
3. 100
4. 50

88. A 6-pole, 3-phase alternator running at 1000 rpm supplies to an 8-pole, 3-phase induction motor which has a rotor current of frequency 2 Hz. The speed at which the motor operates is

1. 1000 rpm
2. 960 rpm
3. 750 rpm
4. 720 rpm

89. A single-phase, 2000 V alternator has armature resistance and reactance of 0.8Ω and 4.94Ω respectively. The voltage regulation of the alternator at 100A load at 0.8 leading power factor is

1. 7%
2. 8.9%
3. 14%
4. 0%

90. In order to eliminate the fifth harmonic voltage from the phase voltage of an alternator, the coil should be pitched by

1. 36°
2. 72°
3. 15°
4. 18°