Synchronous Generator Objectives Part 05

81 . In case of low speed hydrogenators, the short circuit ratio is usually 1.0 to 1.5.

82 . The permissible duration for which a generator of rated frequency 50 Hz can run at 46 Hz is one second

83 . The permissible duration in supply frequency is ± 2 %

84 . The regulation of an alternator is likely to be negative in case of) leading power factor of the load.

85 . A phase, 50 Hz, 6600 V, alternator is rated at 6600 kW at 0.8 power factor and a full load efficiency of 90%.

86 . kVA is rating of the alternator is 7500 kVA

87 . The current rating of the alternator is 6563 A

88 . The input to the alternator is 6666 kW

89 . Which of the following method is likely to give the voltage regulation more than the actual value Synchronous reactance method

90 . The effect of cross magnetization in an alternator field is to make the output non-sinusoidal

91 . In order to reduce the harmonics in the emf generated in an alternator slots are skewed (B) salient pole tips are chamfered (C) winding is well distributed (D) all of the above.

92 . The maximum power in a synchronous machine is obtained when the load angle is 120°

93 . The emf generated due to nth harmonic component of flux in an alternator will be less than the value of fundamental emf.

94 . Synchronizing torque comes into operation under all of the following cases EXCEPT reduction in exciting current in one of the alternators.

95 . Unbalanced 3-phase stator currents cause (A) double frequency currents in the rotor(B) healing of rotor(C) vibrations(D) all of the above.

96 . In large generators protection provided against external faults is (A) biased differential protection (B) sensitive earth fault protection (C) inter-turn fault protection (D) all of the above.

97 . Pitch factor is the ratio of the emfs of short pitch coil to full pitch coil

98 . In an alternator if the winding is short pitched by 50 electrical degrees, its pitch factor will be 0.866

99 . The Potier’s triangle separates armature leakage reactance and armature reaction mm

100 . If a single phase alternator has 8 slots per pole uniformly speed, but the winding is arranged with the middle two left empty, the breadth coefficient will be 0.53