300 Important Alternator MCQ Question and Answer | PDF Free Download
1.The short pitch winding is preferred over full pitch winding for an alternator because it
- AGives improved waveform of the induced emf as the distorting harmonics can be reduced or totally eliminated
- BReduces the inductance of the winding
- CIncreases total induced emf
- DBoth (a) and (b)
2.Harmonics in the emf generated in an alternator can be reduced by
- Askewing the slots
- Bchamfering the salient pole tips
- Cusing distributed winding
- Dall of the above
3.Skew of rotor bar eliminates
- Athe effect of space harmonics
- Bthe entire effect of crawling
- Cmagnetic noise
- Dvibration due to unequal force developed on rotor
4.The emf generated due to nth harmonic components of flux in an alternator will be _____the fundamental emf in magnitude.
- ALess than
- BMore than
- CEqual to
- DNone of the above
5.4 pole star connected alternator running at 1500 rpm have 72 slots with 10 conductors per slot. The number of turns per phase and slot angle is
- A120 turns and 20 degrees
- B100 turns and 10 degrees
- C120 turns and 10 degrees
- D100 runs and 20 degree
6.The stator of a 3-phase, 6-pole ac machine has 45 slots. The stator winding has 45 coils with a coil span of 6 slots. What type of winding will be selected for this machine?
- ADouble layer fractional slot short pitched winding
- BSingle layer fractional slot short pitched winding
- CSingle layer integral slot full pitch winding
- DDouble layer fractional slot full pitch winding
7.Distributed winding and short chording employed in ac machines will result in
- AIncrease in emf and reduction in harmonics
- BReduction in emf and increase in harmonics
- CIncrease in both emf and harmonics
- DReduction in both emf and harmonics
8.It is desirable to eliminate 5th harmonic voltage from the phase voltage of an alternator. The coils should be short pitched by an electrical angle of
- A30 degree
- B36 degree
- C72 degree
- D18 degree
9.In a synchronous generator, a divided winding is preferable to a conventional winding rotor because of
- AHigher efficiency
- BIncreased steady-state stability limit
- CHigher short-circuit ration
- DBetter damping
10.A 4-pole 3 phase, double layer winding is housed in a 36 slot stator for an a ac machine with 60 degree phase spread. Coil span is 7 slot pitches. Number of slots in which top and bottom layers belong to different phases is
- A24
- B18
- C12
- D0
11.The phasor addition of stator and rotor mmfs is possible In a cylindrical rotor synchronous machine because
- ATwo mmfs are rotating in opposite directions
- BTwo mmfs are rotating in same direction at different speeds
- CTwo mmfs are stationary with respect to each other
- DOne mmf is stationary and the other mmf is rotating
12.Three phase alternators are invariably connected in star so as to
- AReduce the size of stator conductors used
- BIncrease the terminal voltage
- CReduce magnetic losses
- DAll of the above
13.The stator winding of an alternator is normally connected in star to eliminate the _____harmonic component of the voltage wave from.
- AThird
- BFifth
- CSeventh
- DNone of the above
14.if the dimensions of all of the parts of a synchronous generator and the number of field and armature turns are doubled, then the generated voltage will change by a factor of
- A1
- B2
- C4
- D8
15.The angle between induced emf and terminal voltage on no load for a single-phase alternator is
- A180 degree
- B90 degree
- C0 degree
- DNone of these
16.The 5th space harmonics in the mmf developed by balanced fundamental frequency armature currents rotate at _____times the synchronous speed with respect to the field
- A5/6
- B6/5
- C5/4
- D5/7
17.The seventh space harmonics in the mmf produced by balanced fundamental frequency armature currents rotate at ____times the synchronous speed with respect to the field.
- A5/7
- B8/7
- C6/7
- D7/6
18.The phase sequence of a three-phase alternator will reverse if
- AThe filed current is reversed keeping the direction of rotation same
- BThe field current remains the same but the direction of rotation is reversed
- CThe field current is reversed and the number of poles is doubled
- DThe number of poles is doubled without reversing the field current.
19.Power factor of an alternator driven by constant prime mover input can be changed by changing the
- ASpeed
- BLoad
- CField excitation
- DPhase sequence
20.The reactive power delivered by a synchronous generator can be controlled by
- AChanging the prime mover input
- BChanging the excitation
- CChanging the direction of rotation
- DChanging the prime mover speed