# MCQ in AC Generators Part 2 | REE Board Exam

(Last Updated On: September 30, 2020) This is the Multiple Choice Questions Part 2 of the Series in AC Generators as one of the Electrical Engineering topic. In Preparation for the REE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electrical Engineering field, Electrical Engineering Books, Journals and other Electrical Engineering References.

#### Continue Practice Exam Test Questions Part 2 of the Series

Choose the letter of the best answer in each questions.

51.  Some engineers prefer ‘lamps bright’ synchronization to ‘lamps dark’ synchronization because

A.  brightness of lamps can be judged easily

B.  it gives sharper and more accurate synchronization

C.  flicker is more pronounced

D.  it can be performed quickly

Solution:

52.  It is never advisable to connect a stationary alternator to live bus-bars because it

A.  is likely to run as synchronous motor

B.  will get short-circuited

C.  will decrease bus-bar voltage through momentarily

D.  will disturb generated e.m.f. of other alternators connected in parallel

Solution:

53.  Two identical alternators are running in parallel and carry equal loads. If excitation of one alternator is increased without changing its steam supply , then

A.  it will keep supplying almost the same load

B.  kVAR supplied by it would decrease

C.  its p.f. will increase

D.  kVA supplied by it would decrease

Solution:

54.  Keeping its excitation constant, if steam supply of an alternator running in parallel with another identical alternator is increased, then

A.  it would over-run the other alternator

B.  its rotor will fall back in phase with respect to the other machine

C.  it will supply greater portion of the load

D.  its power factor would be decreased

Solution:

55.  The load sharing between two steam-driven alternators operating in parallel may be adjusted by varying the

A.  field strengths of the alternators

B.  power factors of the alternators

C.  steam supply to their prime movers

D.  speed of the alternators

Solution:

56.  Squirrel-cage bars placed in the rotor pole faces of an alternator help reduce hunting

A.  above synchronous speed only

B.  below synchronous speed only

C.  above and below synchronous speed both

D.  none of these

Solution:

57.  For a machine on infinite bus active power can be varied by

A.  changing field excitation

B.  changing of prime mover speed

C.  both A and B above

D.  none of these

Solution:

58.  Majority of alternators in the use have

A.  revolving ac armature winding

B.  stationary field type construction

C.  revolving field type construction

D.  none of these

Solution:

59.  The stator of an alternator is identical to that of a

A.  dc generator

B.  3-phase induction motor

C.  1-phase induction motor

D.  Rosenberg generator

Solution:

60.  The stator of an alternator rarely uses _____ slots.

A.  wide-open type

B.  semi-closed type

C.  closed type

D.  none of these

Solution:

61.  The field winding of an alternator is ______ excited.

A.  dc

B.  ac

C.  both dc and ac

D.  none of these

Solution:

62.  The ac armature winding of an alternator operates at ______ the field winding.

A.  the same as

B.  much lesser voltage than

C.  much higher voltage than

D.  none of these

Solution:

63.  The salient-pole construction for field structure of an alternator is generally used for ______ machine.

A.  2-pole

B.  4-pole

C.  8-pole

D.  none of these

Solution:

64.  An alternator is sometimes called ______ generator.

A.  synchronous

B.  asynchronous

C.  Rosenberg

D.  none of these

Solution:

65.  A turbo-alternator uses

A.  salient-pole field structure

B.  non-salient-pole field structure

C.  rotating ac armature winding

D.  none of these

Solution:

66.  The non-salient pole field construction is used for ____ generator.

A.  low-speed

B.  medium-speed

C.  high-speed

D.  none of these

Solution:

67.  The ac armature winding of an alternator is

A.  always star-connected

B.  generally delta-connected

C.  star-delta connected

D.  none of these

Solution:

68.  Low-speed alternators are driven by

A.  hydraulic turbines

B.  steam engines

C.  steam turbines

D.  none of these

Solution:

69.  High-speed alternators are driven by

A.  diesel engines

B.  hydraulic turbines

C.  steam turbines

D.  none of these

Solution:

70.  The air-gap in an alternator is ______ in an induction machine.

A.  much shorter than

B.  much longer than

D.  none of these

Solution:

71.  The stator of an alternator is wound for ______ on the rotor.

A.  more number of poles than

B.  less number of poles than

C.  the same number of poles as

D.  none of these

Solution:

72.  Turbo-alternators have rotors of

A.  small diameter and long axial length

B.  large diameter and long axial length

C.  large diameter and small axial length

D.  same diameter and axial length

Solution:

73.  The rotor of a turbo-alternator is made cylindrical in order to reduce ______.

A.  eddy current loss

B.  hysteresis loss

C.  windage losses

D.  none of these

Solution:

74.  The number of cycles generated in a 6-pole alternator in one revolution is

A.  3

B.  6

C.  50

D.  none of these

Solution:

75.  The speed at which a 6-pole alternator should be driven to generator 50 cycles per second is

A.  1,500 rpm

B.  1,000 rpm

C.  500 rpm

D.  none of these

Solution:

76.  The frequency of emf generated in an 8-pole alternator running at 900 rpm is

A.  50 Hz

B.  60 Hz

C.  120 Hz

D.  none of these

Solution:

77.  In case of a 4-pole machine, 1 mechanical degree corresponds to ____ electrical degree.

A.  2

B.  4

C.  8

D.  none of these

Solution:

78.  For the same rating, the size of low-speed alternator is ____ that of high-speed alternator.

B.  more than

C.  less than

D.  none of these

Solution:

79.  The synchronous reactance of an alternator is due to ____.

A.  leakage flux

B.  d.c. field excitation

C.   armature reaction

D.  none of these

Solution:

80.  The synchronous reactance of an alternator is generally ______ armature resistance.

A.  5 times smaller than

B.  5 times greater than

C.  10 to 100 times greater than

D.  10 times smaller than

Solution:

81.  The synchronous reactance of an alternator ______ as the iron is saturated.

A.  decreases

B.  increases

C.  remains unchanged

D.  none of these

Solution:

82.  In an alternator, the effect of armature reaction is minimum at power factor of ______.

A.  0.866 lagging

C.  0.5 lagging

D.  unity

Solution:

83.  If the lagging load p.f. of an alternator is decreased, the demagnetizing effect of armature reaction ______.

A.  remains the same

B.  is decreased

C.  is increased

D.  none of these

Solution:

84.  A 3-phase alternator generates an open-circuit phase voltage of 4000 V when exciting current is 50 A; the short-circuit current for the same excitation being 800 A. The synchronous reactance per phase is

A.  80 ohms

B.  5 ohms

C.  15 ohms

D.  none of these

Solution:

85.  A 30 MVA, 15 kV alternator will have a per phase nominal impedance of

A.  9 ohms

B.  15 ohms

C.  7.5 ohms

D.  none of these

Solution:

86.  When load on an alternator is increased, the terminal voltage increases if the load pf is

A.  unity

B.  lagging

D.  zero

Solution:

87.  The efficiency of the turbo-alternator ______ with increase in speed.

A.  decreases

B.  increases

C.  remains unchanged

D.  none of these

Solution:

88.  The full-load efficiency of the alternator ______ with the size of the machine.

A.  increases

B.  decreases

C.  remains unchanged

D.  none of these

Solution:

89.  For the same power rating, an alternator is ______ that of a dc generator.

A.  larger in size than

B.  smaller in size than

C.  of the same size as

D.  none of these

Solution:

90.  In the armature winding of an alternator, the coil span falls short of full-pitch by 60° (electrical). The pitch factor is

A.  0.866

B.  0.5

C.  0.25

D.  none of these

Solution:

91.  A 3-phase alternator has 3 slots per pole. The distribution factor of the winding is

A.  0.866

B.  0.5

C.  1

D.  none of these

Solution:

92.  The disadvantage of a short-pitched coil is that

A.  harmonics are introduced

B.  waveform becomes non-sinusoidal

C.  voltage round the coil is reduced

D.  none of these

Solution:

93.  The voltage regulation of an alternator for a pf of 0.8 lagging is ____ at unity pf.

A.  greater than

B.  smaller than

C.  the same as

D.  none of these

Solution:

94.  The voltage regulation of an alternator is larger than that of a dc generator because of

A.  larger armature resistance

B.  large leakage reactance

C.  complex effects of armature reaction

D.  none of these

Solution:

95.  The per phase dc armature resistance of an alternator is 0.5 ohm. The effective ac armature resistance would be about

A.  0.5 ohm

B.  0.75 ohm

C.  4 ohms

D.  0.25 ohm

Solution:

96.  The dc armature resistance of a Y-connected alternator measured across its two terminals is 0.5 ohm. The per phase resistance is

A.  0.5 ohm

B.  1 ohm

C.  0.25 ohm

D.  1.5 ohms

Solution:

97.  The dc armature resistance of a delta-connected alternator measured across its two terminals is 1 ohm. The per phase dc resistance is

A.  3 ohms

B.  1.5 ohms

C.  0.33 ohm

D.  none of these

Solution:

98.  The under excited alternator supplies ______.

A.  lagging VAR

C.  no reactive power

D.  none of these

Solution:

99.  If the excitation of an alternator operating in parallel with other alternators is decreased, its

B.  pf becomes more lagging

C.  output kW will change

D.  none of these

Solution:

100.  The distribution of load between two alternators operating in parallel can be changed by changing

A.  phase sequence

B.  field excitation of alternators

C.  driving torques of prime movers

D.  none of these

Solution:

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