Synchronous Generator Objectives Part 04
61 . If the input to the prime mover of an alternator is kept constant but the excitation is changed then the (reactive component of the output is changed
62 . If two machines are running in synchronism and the voltage of one machine is suddenly increased synchronising torque will be produced to restore further synchronism.
63 . In an alternator, at 0.8 lagging power factor, the generated voltage per phase is 240 V to give a rated terminated voltage ‘ V ‘. If the power factor of load increases to unity, the generated voltage per phase must be 225 V.
64 . The advantage of salient poles in an alternator is adoptability to low and medium speed operation
65 . Magnetisation curves for no load and full load unity power factor are shown in figure below. Which is the magnetisation curve for full load 0.8 power factor ?
66 . At a particular instant a turbo alternator is generating 80 MW at 0.8 power factor lagging. Now if the steam supply valve to the steam turbine is further opened and the excitation is not changed the speed of the alternator will remain unchanged but it can meet more kW demand
67 . Two alternators A and B are sharing a resistive load (p.f. = 1) equally. Now if the excitation of alternator A is increased alternator A will become lagging and alternator B will become leading
68 . The advantage of providing damper winding in alternators is (A) elimination of harmonic effects (B) provide a low resistance path for the currents due to unbalancing of voltage (C) oscillations are provided when two alternators operate in parallel (D) all of the above.
69 . When two alternators are running in exactly synchronism, the synchronising power wil be (zero
70 . Load characteristic curves for an alternator are shown. The curves are drawn for 0.8 pf lagging, 0.8 p.f. leading, 0.7 p.f. leading and 0.9 p.f. lagging. Which curve representsthe characteristics for 0.8 p.f. leading ?
71 . Which curve represents the data for 0.8 p.f. lagging ? (A) curve A
72 . Which curve represents the data for 0.9 p.f. lagging ? (B) curve B
73 . The balanced short circuit current of a three phase alternator is 25 amperes at 1500 rpm. For the same field current, the balanced short current at 1400 rpm will be 20 A
74 . A three phase alternator has a phase sequence of RYB for its three output voltages, for clockwise rotation. Now if the alternator is rotated anticlockwise, the phase sequence will be RBY
75 . In a synchronous machine, if the field flux axis is ahead of the armature field axis, in the direction of rotation, the machine working as synchronous generator.
76 . In synchronous alternator, which of the following coils will have emf closer to sine waveform? distributed winding in short pitch coils.
77 . An alternator has rated field current of 4 A. The alternator develops 180 V while drawing a field current of 2 A at 750 rpm. If the field current is made 4 A at 750 rpm generated voltage could be 330 V.
78 . The armature reaction of an alternator will be completely magnetizing in case the load power factor is zero loading.
79 . Which of the following is not an integral part of synchronous generator system? distribution transformer
80 . For turbo generators the range of excitation voltage is 100 to 800 V