DC Generator Questions And Answers: DC Generator MCQs

DC Generator Questions And Answers. Multiple Choice Questions and Answers related to D.C Generators in Electrical Engineering.

 

DC Generator Questions And Answers 

 

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

View Answer

D. direction of motion of conductor, if forefinger points along the lines of flux

 

According to Fleming’s right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of ?

A. motion of conductor
B. lines of force
C. either of the above
D. none of the above

View Answer

B. lines of force

 

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

View Answer

D. any of the above

 

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

View Answer

B. Wave winding

 

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

View Answer

C. 0.5 m

 

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

A. current
B. voltage
C. speed
D. none of above

View Answer

C. speed

 

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

View Answer

B. magnetic flux, direction of motion and the direction of e.m.f. induced

 

DC Generator Questions And Answers

 

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

View Answer

D. all above

 

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

View Answer

A. commutator

 

Equilizer rings are required in case armature is ?

A. wave wound
B. lap wound
C. delta wound
D. duplex wound

View Answer

B. lap wound

 

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

View Answer

B. field resistance less than the critical resistance

 

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

View Answer

A. Blv

 

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

View Answer

B. 8

 

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

View Answer

C. induction motor D.C. generator set

 

DC Generator Questions And Answers

 

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

A. to reduce the reluctance of the mag¬netic 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

View Answer

D. to discharge all the above functions

 

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

View Answer

C. lie under interpolar region

 

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

View Answer

D. difference of front and back pitches

 

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

View Answer

C. crossmagnetisation as well as demagnetising

 

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

View Answer

D. amount of current to be collected

 

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

View Answer

D. 580 V

 

The following constitute short-circuit in the armature winding ?

A. Insulation failure between two commutator bars
B. Insulation failure between two turns of a coil
C. Two of more turns of the same coil getting grounded
D. All of the above

View Answer

D. All of the above

 

DC Generator Questions And Answers

 

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

A. brushes
B. field
C. armature
D. load

View Answer

B. field

 

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

View Answer

B. Commutator

 

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
D. none

View Answer

A. just ahead of magnetic neutral axis

 

The rapid wear of brushes takes place due to ?

A. abrasion from dust
B. excessive spring pressure
C. rough commutator bars
D. high mica insulation between com-mutation bars
E. all of the above factors

View Answer

E. all of the above factors

 

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

View Answer

D. Equilizing bus bars are used with parallel running of D.C. shunt generators

 

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

View Answer

A. along neutral axis

 

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

A. cumulatively compounded long shunt
B. deferentially compounded long shunt
C. cumulatively compounded short shunt
D. differentially compounded short shunt

View Answer

B. deferentially compounded long shunt

 

DC Generator Questions And Answers

 

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

View Answer

B. 3 : 1

 

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

View Answer

A. reduces generator e.m.f.

 

Number of tappings for each equalizer ring is equal to ?

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

View Answer

A. number of pole pairs

 

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
D. None

View Answer

A. the brushes of opposite polarity should track each other

 

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

View Answer

C. Metal graphite brushes

 

DC Generator Questions And Answers

 

The e.m.f. generated by a shunt wound D.C. generator is E. 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

View Answer

B. 2E

 

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

View Answer

D. self-excited generator

 

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

A. rotor
B. stator
C. field
D. armature

View Answer

D. armature

 

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

View Answer

C. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil

 

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

View Answer

D. iron loss and mechanical loss

 

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

View Answer

D. all of the above

 

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

View Answer

D. number of poles is 2

 

DC Generator Questions And Answers

 

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

View Answer

A. any even number of conductors

 

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

View Answer

A. Series generator

 

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

View Answer

A. Series generator

 

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

View Answer

D. series fields of all generators should be either on positive side or negative side of the armature

 

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

View Answer

D. None of the above

 

Permeance is the reciprocal of ?

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

View Answer

B. reluctance

 

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

View Answer

C. 240 V

 

DC Generator Questions And Answers

 

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

View Answer

B. about 2 V

 

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

View Answer

A. is the same as that of the main pole ahead

 

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

View Answer

A. zero

 

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

View Answer

B. equal to no-load terminal voltage

 

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

View Answer

D. Shunt field

 

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

View Answer

B. dummy coils

 

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

View Answer

D. commutation

 

DC Generator Questions And Answers

 

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

A. sinusoidal
B. triangular
C. pulsating
D. flat topped

View Answer

D. flat topped

 

The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is ?

A. 2
B. 4
C. 6
D. 8

View Answer

B. 4

 

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

View Answer
\

C. Level compounded generator

 

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

View Answer

C. that even number which is exact multiple of poles + 2

 

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

View Answer

A. Shunt generators

 

For both lap and wave windings, there are as many commutator bars as the number of ?

A. slots
B. armature conductors
C. winding elements
D. poles

View Answer

C. winding elements

 

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

View Answer

D. That generator takes large share of loads

 

DC Generator Questions And Answers

 

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

A. to increase the series flux
B. to increase the generated e.m.f.
C. to reduce the combined effect of ar-mature reaction of both the machines
D. so that the two identical machines will pass approximately equal cur¬rents to the load

View Answer

D. so that the two identical machines will pass approximately equal cur¬rents to the load

 

The essential condition for parallel operation of two D.C. generators is that they have ?

A. same kW rating
B. the same operation r.p.m.
C. the same drooping voltage characteristics
D. same percentage regulation

View Answer

C. the same drooping voltage characteristics

 

Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be ?

A. 270 V
B. 267.5 V
C. 265 V
D. 257.4 V

View Answer

B. 267.5 V

 

As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately ?

A. 40 percent
B. 25 percent
C. 10 percent
D. 5 percent

View Answer

D. 5 percent

 

Shunt generators are most suited for stable parallel operation because of their ?

A. rising voltage characteristics
B. identical voltage characteristics
C. drooping voltage characteristics
D. linear voltage characteristics

View Answer

C. drooping voltage characteristics

 

A shunt generator can self-excite ?

A. only if the resistance of the field circuit is less than critical value
B. only if the resistance of the field circuit is greater than critical value
C. irrespective of the value of the resistance in the field circuit
D. none

View Answer

A. only if the resistance of the field circuit is less than critical value

 

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 armature reaction of both machines

View Answer

C. so that two similar machines will pass approximately equal currents to the load

 

DC Generator Questions And Answers

 

The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be ?

A. 150 V
B. less than 150 V
C. greater than 150 V
D. none of the above

View Answer

C. greater than 150 V

 

The main factor which leads to unstable parallel operation of flat and over compounded generators is ?

A. their rising voltage characteristics
B. unequal number of turns in their series field windings
C. unequal speed regulation of their primemovers
D. unequal series field resistances

View Answer

A. their rising voltage characteristics

 

The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage ?

A. will be less than 250 V
B. will always be 250 V
C. may be greater or less than 250 V
D. none of the above

View Answer

C. may be greater or less than 250 V

 

If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to ?

A. reverse the field connections
B. increase the field resistance
C. increase the speed of primemover
D. check armature insulation resistance

View Answer

A. reverse the field connections

 

A series generator can self-excite ?

A. only if the load current is zero
B. only if the load current is not zero
C. irrespective of the value of load current
D. none of the above

View Answer

B. only if the load current is not zero

 

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