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Electrical Engineering
D.C. Generators
Quiz 3
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Q.1
Equalizer rings are required in case armature is
Wave wound
Lap wound
Delta wound
Duplex wound
Q.2
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
Motion of conductor
Lines of force
Either of the above
None of the above
Q.3
If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
Zero
Small
The same as rated voltage
High
Q.4
In D.C. generators, current to the external circuit from armature is given through
Commutator
Solid connection
Slip rings
None of above
Q.5
In a four-pole D.C. machine
All the four poles are north poles
Alternate poles are north and south
All the four poles are south poles
Two north poles follow two south poles
Q.6
The demagnetizing component of armature reaction in a D.C. generator
Reduces generator e.m.f.
Increases armature speed
Reduces interpoles flux density
Results in sparking trouble
Q.7
In D.C. generators, lap winding is used for
High voltage, high current
Low voltage, high current
High voltage, low current
Low voltage, low current
Q.8
Copper brushes in D.C. machine are used
Where low voltage and high currents are involved
Where high voltage and small currents are involved
In both of the above cases
In none of the above cases
Q.9
Which of the following generators will be preferred if they are required to be run in parallel?
Shunt generators
Series generators
Compound generators
None of the above
Q.10
In over compounded generator, full load terminal voltage is
Almost zero
Less than no load terminal voltage
More than no load terminal voltage
Equal to no-load terminal voltage
Q.11
The rapid wear of brushes takes place due to
Abrasion from dust
Excessive spring pressure
Rough commutator bars
All of the above factors
Q.12
In case of D.C. machine winding, number of commutator segments is equal to
Number of armature coils
Number of armature coil sides
Number of armature conductors
Number of armature turns
Q.13
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.
Series field
Compensating field
Inter pole field
Shunt field
Q.14
The essential condition for parallel operation of two D.C. generators is that they have
same kW rating
the same operation r.p.m.
the same drooping voltage characteristics
same percentage regulation
Q.15
In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralized by all of the following except
Interpoles
Dummy coils
Compensating winding
Shifting of axis of brushes
Q.16
The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
Will be less than 250 V
Will always be 250 V
May be greater or less than 250 V
None of the above
Q.17
While applying Fleming's right-hand rule to and the direction of induced e.m.f., the thumb points towards
Direction of induced e.m.f.
Direction of flux
Direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
Direction of motion of conductor, if forefinger points along the lines of flux
Q.18
The voltage drop for which of the following types of brush can be expected to be least?
Graphite brushes
Carbon brushes
Metal graphite brushes
None of the above
Q.19
In a D.C. machine stray loss is the sum of
Total copper loss and mechanical loss
Armature copper loss and iron loss
Shunt field copper loss and mechanical loss
Iron loss and mechanical loss
Q.20
As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately
40 percent
25 percent
10 percent
5 percent
Q.21
An exciter for a turbo generator is a
Separately excited generator
Shunt generator
Series generator
Compound generator
Q.22
Laminations of core are generally made of
Case iron
Carbon
Silicon steel
Stainless steel
Q.23
In D.C. generators on no-load, the air gap flux distribution in space is
Sinusoidal
Triangular
Pulsating
Flat topped
Q.24
The purpose of providing dummy coils in a generator is
To reduce eddy current losses
To enhance flux density
To amplify voltage
To provide mechanical balance for the rotor
Q.25
Brushes of D.C. machines are made of
Carbon
Soft copper
Hard copper
All of above
Q.26
The insulating material used between the commutator segments is normally
Graphite
Paper
Mica
Insulating varnish
Q.27
The bearings used to support the rotor shafts are generally
Ball bearings
Bush bearings
Magnetic bearings
Needle bearings
Q.28
When two D.C. series generators are running in parallel, an equalizer bar is used
To increase the speed and hence generated e.m.f.
To increase the series flux
So that two similar machines will pass approximately equal currents to the load
To reduce the combined effect of armature reaction of both machines
Q.29
When two D.C. generators are running in parallel an equalizer bar is used
To increase the series flux
To increase the generated e.m.f.
To reduce the combined effect of armature reaction of both the machines
So that the two identical machines will pass approximately equal currents to the load
Q.30
D.C. generator generally preferred for charging automobile batteries is
Series generator
Shunt generator
Long shunt compound generator
Any of the above
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