170+ DC Generators Solved MCQs

1.

Laminations of core are generally made of

A. case iron
B. carbon
C. silicon steel
D. stainless steel
Answer» C. silicon steel
2.

Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ?

A. 0.005 mm
B. 0.05 mm
C. 0.5 m
D. 5 m
Answer» C. 0.5 m
3.

The armature of D.C. generator is laminated to

A. reduce the bulk
B. provide the bulk
C. insulate the core
D. reduce eddy current loss
Answer» D. reduce eddy current loss
4.

The resistance of armature winding depends on

A. length of conductor
B. cross-sectional area of the conductor
C. number of conductors
D. all of the above
Answer» D. all of the above
5.

The field coils of D.C. generator are usually made of

A. mica
B. copper
C. cast iron
D. carbon
Answer» B. copper
6.

The commutator segments are connected to the armature conductors by means of

A. copper lugs
B. resistance wires
C. insulation pads
D. brazing
Answer» A. copper lugs
7.

In a commutator

A. copper is harder than mica
B. mica and copper are equally hard
C. mica is harder than copper
D. none of the above
Answer» C. mica is harder than copper
8.

In D.C. generators the pole shoes are fastened to the pole core by

A. rivets
B. counter sunk screws
C. brazing
D. welding
Answer» B. counter sunk screws
9.

Satisfactory commutation of D.C. machines requires

A. brushes should be of proper grade and size
B. brushes should smoothly run in the holders
C. smooth, concentric commutator properly undercut
D. all of the above
Answer» D. all of the above
10.

Fleming's right-hand rule regarding direction of induced e.m.f., correlates

A. magnetic flux, direction of current flow and resultant force
B. magnetic flux, direction of motion and the direction of e.m.f. induced
C. magnetic field strength, induced voltage and current
D. magnetic flux, direction of force and direction of motion of conductor
Answer» B. magnetic flux, direction of motion and the direction of e.m.f. induced
11.

While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards

A. direction of induced e.m.f.
B. direction of flux
C. direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
D. direction of motion of conductor, if forefinger points along the lines of flux
Answer» D. direction of motion of conductor, if forefinger points along the lines of flux
12.

The bearings used to support the rotor shafts are generally

A. ball bearings
B. bush bearings
C. magnetic bearmgs
D. needle bearings
Answer» A. ball bearings
13.

In D.C. generators, the cause of rapid brush wear may be

A. severe sparking
B. rough commutator surface
C. imperfect contact
D. any of the above
Answer» D. any of the above
14.

In lap winding, the number of brushes is always

A. double the number of poles
B. same as the number of poles
C. half the number of poles
D. two
Answer» B. same as the number of poles
15.

For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?

A. Lap winding
B. Wave winding
C. Either of (a) and (b) above
D. Depends on other features of design
Answer» B. Wave winding
16.

In a four-pole D.C. machine

A. all the four poles are north poles
B. alternate poles are north and south
C. all the four poles are south poles
D. two north poles follow two south poles
Answer» B. alternate poles are north and south
17.

Copper brushes in D.C. machine are used

A. where low voltage and high currents are involved
B. where high voltage and small cur-rents are involved
C. in both of the above cases
D. in none of the above cases
Answer» A. where low voltage and high currents are involved
18.

A separately excited generator as compared to a self-excited generator

A. is amenable to better voltage con-trol
B. is more stable
C. has exciting current independent of load current
D. has all above features
Answer» D. has all above features
19.

In case of D.C. machines, mechanical losses are primary function of

A. current
B. voltage
C. speed
D. none of above
Answer» C. speed
20.

Iron losses in a D.C. machine are independent of variations in

A. speed
B. load
C. voltage
D. speed and voltage
Answer» B. load
21.

In D.C. generators, current to the external circuit from armature is given through

A. commutator
B. solid connection
C. slip rings
D. none of above
Answer» A. commutator
22.

Brushes of D.C. machines are made of

A. carbon
B. soft copper
C. hard copper
D. all of above
Answer» A. carbon
23.

If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by

A. Blv
B. Blv2
C. Bl2v
D. Bl2v2
Answer» A. Blv
24.

In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be

A. 4
B. 8
C. 16
D. 32
Answer» B. 8
25.

The material for commutator brushes is generally

A. mica
B. copper
C. cast iron
D. carbon
Answer» D. carbon
26.

The insulating material used between the commutator segments is normally

A. graphite
B. paper
C. mica
D. insulating varnish
Answer» C. mica
27.

In D.C. generators, the brushes on commutator remain in contact with conductors which

A. lie under south pole
B. lie under north pole
C. lie under interpolar region
D. are farthest from the poles
Answer» C. lie under interpolar region
28.

If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be

A. demagnetisation only
B. cross magnetisation as well as magnetisation
C. crossmagnetisation as well as demagnetising
D. cross magnetisation only
Answer» C. crossmagnetisation as well as demagnetising
29.

Armature reaction of an unsaturated D.C. machine is

A. crossmagnetising
B. demagnetising
C. magnetising
D. none of above
Answer» A. crossmagnetising
30.

D.C. generators are connected to the busbars or disconnected from them only under the floating condition

A. to avoid sudden loading of the primemover
B. to avoid mechanicaljerk to the shaft
C. to avoid burning of switch contacts
D. all above
Answer» D. all above
31.

Eddy currents are induced in the pole shoes of a D.C. machine due to

A. oscillating magnetic field
B. pulsating magnetic flux
C. relative rotation between field and armature
D. all above
Answer» C. relative rotation between field and armature
32.

Equilizer rings are required in case armature is

A. wave wound
B. lap wound
C. delta wound
D. duplex wound
Answer» B. lap wound
33.

Welding generator will have

A. lap winding
B. wave winding
C. delta winding
D. duplex wave winding
Answer» A. lap winding
34.

In case of D.C. machine winding, number of commutator segments is equal to

A. number of armature coils
B. number of armature coil sides
C. number of armature conductors
D. number of armature turns
Answer» A. number of armature coils
35.

For a D.C. machines laboratory following type of D.C. supply will be suitable

A. rotary converter
B. mercury are rectifier
C. induction motor D.C. generator set
D. synchronous motor D.C. generator set
Answer» C. induction motor D.C. generator set
36.

The function of pole shoes in the case of D.C. machine is

A. to reduce the reluctance of the magnetic path
B. to spread out the flux to achieve uniform flux density
C. to support the field coil
D. to discharge all the above functions
Answer» D. to discharge all the above functions
37.

In the case of lap winding resultant pitch is

A. multiplication of front and back pitches
B. division of front pitch by back pitch
C. sum of front and back pitches
D. difference of front and back pitches
Answer» D. difference of front and back pitches
38.

A D.C. welding generator has

A. lap winding
B. wave moving
C. duplex winding
D. any of the above
Answer» A. lap winding
39.

Which of the following statement about D.C. generators is false ?

A. Compensating winding in a D.C. machine helps in commutation
B. In a D. C. generator interpoles winding is connected in series with the armature winding
C. Back pitch and front pitch are both odd and approximately equal to the pole pitch
D. Equilizing bus bars are used with parallel running of D.C. shunt generators
Answer» D. Equilizing bus bars are used with parallel running of D.C. shunt generators
40.

The demagnetising component of armature reaction in a D.C. generator

A. reduces generator e.m.f.
B. increases armature speed
C. reduces interpoles flux density
D. results in sparking trouble
Answer» A. reduces generator e.m.f.
41.

Magnetic field in a D.C. generator is produced by

A. electromagnets
B. permanent magnets
C. both (a) and (b)
D. none of the above
Answer» A. electromagnets
42.

The number of brushes in a commutator depends on

A. speed of armature
B. type of winding
C. voltage
D. amount of current to be collected
Answer» D. amount of current to be collected
43.

Compensating windings are used in D.C. generators

A. mainly to reduce the eddy currents by providing local short-circuits
B. to provide path for the circulation of cooling air
C. to neutralise the cross-magnetising effect of the armature reaction
D. none of the above
Answer» C. to neutralise the cross-magnetising effect of the armature reaction
44.

Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?

A. Dummy coils
B. Commutator
C. Eye bolt
D. Equilizer rings
Answer» B. Commutator
45.

In a D.C. generator the ripples in the direct e.m.f. generated are reduced by

A. using conductor of annealed copper
B. using commutator with large number of segments
C. using carbon brushes of superior quality
D. using equiliser rings
Answer» C. using carbon brushes of superior quality
46.

In D.C. generators, lap winding is used for

A. high voltage, high current
B. low voltage, high current
C. high voltage, low current
D. low voltage, low current
Answer» B. low voltage, high current
47.

Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be

A. 2 : 3
B. 3 : 1
C. 3 : 2
D. 1 : 3
Answer» B. 3 : 1
48.

The voltage drop for which of the following types of brush can be expected to be least ?

A. Graphite brushes
B. Carbon brushes
C. Metal graphite brushes
D. None of the above
Answer» C. Metal graphite brushes
49.

The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be

A. E/2
B. 2E
C. slightly less than E
D. E
Answer» B. 2E
50.

The armature core of a D.C. generator is usually made of

A. silicon steel
B. copper
C. non-ferrous material
D. cast-iron
Answer» A. silicon steel
51.

Open circuited armature coil of a D.C. machine is

A. identified by the scarring of the commutator segment to which open circuited coil is connected
B. indicated by a spark completely around the commutator
C. both (a) and (b)
D. none of the above
Answer» C. both (a) and (b)
52.

For the parallel operation of two or more D.C. compound generators, we should ensure that

A. voltage of the incoming generator should be same as that of bus bar
B. polarity of incoming generator should be same as that of bus bar
C. all the series fields should be run in parallel by means of equilizer connection
D. series fields of all generators should be either on positive side or negative side of the armature
Answer» D. series fields of all generators should be either on positive side or negative side of the armature
53.

D.C. series generator is used

A. to supply traction load
B. to supply industrial load at constant voltage
C. voltage at the toad end of the feeder
D. for none of the above purpose
Answer» C. voltage at the toad end of the feeder
54.

Following D.C. generator will be in a position to build up without any residual magnetism in the poles

A. series generator
B. shunt generator
C. compound generator
D. self-excited generator
Answer» D. self-excited generator
55.

Interpole flux should be sufficient to

A. neutralise the commutating self induced e.m.f.
B. neutralise the armature reaction flux
C. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
D. perform none of the above functions
Answer» C. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
56.

D.C. generator generally preferred for charging automobile batteries is

A. series generator
B. shunt generator
C. long shunt compound generator
D. any of'the above
Answer» C. long shunt compound generator
57.

In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when

A. r.p.m. is more than 300
B. r.p.m. is less than 300
C. number of poles is 4
D. number of poles is 2
Answer» D. number of poles is 2
58.

Permeance is the reciprocal of

A. flux density
B. reluctance
C. ampere-turns
D. resistance
Answer» B. reluctance
59.

In D.C. generators the polarity of the interpoles

A. is the same as that of the main pole ahead
B. is the same as that of the immediately preceding pole
C. is opposite to that of the main pole ahead
D. is neutral as these poles do not play part in generating e.m.f.
Answer» A. is the same as that of the main pole ahead
60.

The e.m.f. generated in a D.C. generator is directly proportional to

A. flux/pole
B. speed of armature
C. number of poles
D. all of the above
Answer» D. all of the above
61.

In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except

A. interpoles
B. dummy coils
C. compensating winding
D. shifting of axis of brushes
Answer» B. dummy coils
62.

In D.C. generators on no-load, the air gap flux distribution in space is

A. sinusoidal
B. triangular
C. pulsating
D. flat topped
Answer» D. flat topped
63.

A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly

A. 150 V
B. 175 V
C. 240 V
D. 290 V
Answer» C. 240 V
64.

The purpose of providing dummy coils in a generator is

A. to reduce eddy current losses
B. to enhance flux density
C. to amplify voltage
D. to provide mechanical balance for the rotor
Answer» D. to provide mechanical balance for the rotor
65.

If a D.C. generator fails to build up the probable cause could not be

A. imperfect brush contact
B. field resistance less than the critical resistance
C. no residual magnetism in the generator
D. faulty shunt connections tending to reduce the residual magnetism
Answer» B. field resistance less than the critical resistance
66.

Flashing the field of D.C. generator means

A. neutralising residual magnetism
B. creating residual magnetism by a D.C. source
C. making the magnetic losses of forces parallel
D. increasing flux density by adding extra turns of windings on poles
Answer» B. creating residual magnetism by a D.C. source
67.

The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be

A. 640 V
B. 620 V
C. 600 V
D. 580 V
Answer» D. 580 V
68.

In a D.C. generator the critical resistance refers to the resistance of

A. brushes
B. field
C. armature
D. load
Answer» B. field
69.

To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them

A. just ahead of magnetic neutral axis
B. in magnetic neutral axis
C. just behind the magnetic neutral axis
Answer» A. just ahead of magnetic neutral axis
70.

Armature coil is short circuited by brushes when it lies

A. along neutral axis
B. along field axis
C. in any of the above positions
D. in none of the above positions
Answer» A. along neutral axis
71.

A cumulatively compounded long shunt generator when operating as a motor would be

A. cumulatively compounded long shunt
B. differentially compounded long shunt
C. cumulatively compounded short shunt
D. differentially compounded short shunt
Answer» B. differentially compounded long shunt
72.

To avoid formation of grooves in the commutator of a D.C. machine

A. the brushes of opposite polarity should track each other
B. the brushes of same polarity should track each other
C. brush position has no effect on the commutator grooving
Answer» A. the brushes of opposite polarity should track each other
73.

The rapid wear of brushes takes place due to

A. abrasion from dust
B. excessive spring pressure
C. rough commutator bars
D. all of the above factors
Answer» D. all of the above factors
74.

Number of tappings for each equilizer ring is equal to

A. number of pole pairs
B. number of poles
C. number of parallel paths
D. number of commutator segments
Answer» A. number of pole pairs
75.

A D.C. generator can be considered as

A. rectifier
B. primemover
C. rotating amplifier
D. power pump
Answer» C. rotating amplifier
76.

In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called

A. rotor
B. stator
C. field
D. armature
Answer» D. armature
77.

In a D.C. machine stray loss is the sum of

A. total copper loss and mechanical loss
B. armature copper loss and iron loss
C. shunt field copper loss and mechanical loss
D. iron loss and mechanical loss
Answer» D. iron loss and mechanical loss
78.

Lap winding is composed of

A. any even number of conductors
B. any odd number of conductors
C. that even number which is exact multiple of poles + 2
D. that even number which is exact multiple of poles
Answer» A. any even number of conductors
79.

In a D.C. generator in case the resistance of the field winding is increased, then output voltage will

A. increase
B. decrease
C. remain unaffected
D. fluctuate heavily
Answer» B. decrease
80.

An exciter for a turbo generator is a

A. separately excited generator
B. shunt generator
C. series generator
D. compound generator
Answer» B. shunt generator
81.

In case of a flat compounded generator

A. voltage generated is less than the rated voltage
B. generated voltage is proportional to the load on the generator
C. voltage remains constant irrespec¬tive of the load
D. speed varies in proportion to the load on the generator
Answer» C. voltage remains constant irrespec¬tive of the load
82.

Which of the following generator will have negligible terminal voltage while running on no-load ?

A. Series generator
B. Shunt generator
C. Compound generator
D. Separately excited generator
Answer» A. Series generator
83.

Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?

A. Series generator
B. Shunt generator
C. Compound generator
D. None of the above
Answer» D. None of the above
84.

In over compounded generator, full load terminal voltage is

A. almost zero
B. less than noload terminal voltage
C. more than noload terminal voltage
D. equal to no-load terminal voltage
Answer» C. more than noload terminal voltage
85.

In a level compounded D.C. generator, full load terminal voltage is

A. negligibly low
B. equal to no-load terminal voltage
C. more than no-load terminal voltage
D. less than no-load terminal voltage
Answer» B. equal to no-load terminal voltage
86.

The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except

A. armature reaction
B. armature resistance drop
C. field weakening due to armature reaction and armature
D. commutation
Answer» D. commutation
87.

In a D.C. generator

A. external resistance = internal char-acteristic - armature reaction
B. internal characteristic = magnetisation characteristic - ohmic drop
C. external characteristic = magnetisation characteristic - ohmic drop - armature reaction
D. magnetisation characteristic = external characteristic
Answer» C. external characteristic = magnetisation characteristic - ohmic drop - armature reaction
88.

A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave

A. will be zero
B. will be of 5 Hz
C. willbeof5xiVHz
D. will be of v Hz 5
Answer» B. will be of 5 Hz
89.

A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be

A. zero
B. about 2 V
C. about 50 V
D. 220 V
Answer» B. about 2 V
90.

In a separately excited generator supplying rated load the armature reaction ,

A. is always present
B. is always absent
C. may be sometimes present
D. none of the above
Answer» A. is always present
91.

If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be

A. zero
B. small
C. the same as rated voltage
D. high
Answer» A. zero
92.

Armature reaction in a generator results in

A. demagnetisation of leading pole tip and magnetisation of trailing pole tip
B. demagnetisation of trailing pole tip and magnetisation of leading pole tip
C. damagnetising the centre of all poles
D. magnetising the centre of all poles
Answer» A. demagnetisation of leading pole tip and magnetisation of trailing pole tip
93.

Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.

A. Series field
B. Compensating field
C. Inter pole field
D. Shunt field
Answer» D. Shunt field
94.

Wave winding is composed of

A. any even number of conductors
B. any odd number of conductors
C. that even number which is exact multiple of poles + 2
D. that even number which is exact multiple of poles
Answer» C. that even number which is exact multiple of poles + 2
95.

The critical resistance of the D.C. generator is the resistance of

A. field
B. brushes
C. armature
D. load
Answer» A. field
96.

When two D.C. series generators are running in parallel, an equilizer bar is used

A. to increase the speed and hence generated e.m.f.
B. to increase the series flux
C. so that two similar machines will pass approximately equal currents to the load
D. to reduce the combined effect of ar-mature reaction of both machines
Answer» C. so that two similar machines will pass approximately equal currents to the load
97.

Which of the following generating machine will offer constant voltage on all loads ?

A. Self-excited generator
B. Separately excited generator
C. Level compounded generator .
D. All of the above
Answer» C. Level compounded generator .
98.

Which of the following generators will be preferred if they are required to be run in parallel ?

A. Shunt generators
B. Series generators
C. Compound generators
D. None of the above
Answer» A. Shunt generators
99.

Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?

A. The direction of that generator is reversed
B. The speed of that generator is increased
C. The field of that generator is weakened
D. That generator takes large share of loads
Answer» D. That generator takes large share of loads
100.

A D.C. generator works on the principle of

A. Lenz's law
B. Ohm's law
C. Faraday's law of electromagnetic induction
D. none of the above
Answer» C. Faraday's law of electromagnetic induction
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