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Electrical Engineering
D.C. Generators
Quiz 2
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Q.1
Armature coil is short circuited by brushes when it lies
Along neutral axis
Along field axis
In any of the above positions
In none of the above positions
Q.2
Satisfactory commutation of D.C. machines requires
Brushes should be of proper grade and size
Brushes should smoothly run in the holders
Smooth, concentric commutator properly undercut
All of the above
Q.3
The e.m.f. generated in a D.C. generator is directly proportional to
Flux/pole
Speed of armature
Number of poles
All of the above
Q.4
A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
Zero
About 2 V
About 50 V
220 V
Q.5
Two generators are running in parallel. One of the generators may run as motor for which of the following reasons?
The direction of that generator is reversed
The speed of that generator is increased
The field of that generator is weakened
That generator takes large share of loads
Q.6
The function of pole shoes in the case of D.C. machine is
To reduce the reluctance of the magnetic path
To spread out the flux to achieve uniform flux density
To support the field coil
To discharge all the above functions
Q.7
In case of a 4 pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
4
8
16
32
Q.8
The resistance of armature winding depends on
Length of conductor
Cross-sectional area of the conductor
Number of conductors
All of the above
Q.9
A D.C. welding generator has
Lap winding
Wave moving
Duplex winding
Any of the above
Q.10
If a D.C. generator fails to build up the probable cause could not be
Imperfect brush contact
Field resistance less than the critical resistance
No residual magnetism in the generator
Faulty shunt connections tending to reduce the residual magnetism
Q.11
Armature reaction of an unsaturated D.C. machine is
Cross-magnetizing
Demagnetizing
Magnetizing
None of above
Q.12
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
2 : 3
3 : 1
3 : 2
1 : 3
Q.13
A shunt generator can self-excite
Only if the resistance of the field circuit is less than critical value
Only if the resistance of the field circuit is greater than critical value
Irrespective of the value of the resistance in the field circuit
None of the above
Q.14
In a D.C. generator the critical resistance can be increased by
Increasing its field resistance
Decreasing its field resistance
Increasing its speed
Decreasing its speed
Q.15
In a D.C. machine, short-circuited field coil will result in
odour of barning insulation
unbalanced magnetic pull producing vibrations
reduction of generated voltage for which excitation has to be increased to maintain the voltage
all above
Q.16
In a level compounded D.C. generator, full load terminal voltage is
Negligibly low
Equal to no-load terminal voltage
More than no-load terminal voltage
Less than no-load terminal voltage
Q.17
The field coils of D.C. generator are usually made of
Mica
Copper
Cast iron
Carbon
Q.18
A cumulatively compounded long shunt generator when operating as a motor would be
Cumulatively compounded long shunt
Differentially compounded long shunt
Cumulatively compounded short shunt
Differentially compounded short shunt
Q.19
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
Blv
Blv²
Bl²v
Bl²v²
Q.20
In a D.C. generator in case the resistance of the field winding is increased, then output voltage will
Increase
Decrease
Remain unaffected
Fluctuate heavily
Q.21
In case of D.C. machines, mechanical losses are primary function of
Current
Voltage
Speed
None of above
Q.22
For the parallel operation of two or more D.C. compound generators, we should ensure that
Voltage of the incoming generator should be same as that of bus bar
Polarity of incoming generator should be same as that of bus bar
All the series fields should be run in parallel by means of equalizer connection
Series fields of all generators should be either on positive side or negative side of the armature
Q.23
Eddy currents are induced in the pole shoes of a D.C. machine due to
Oscillating magnetic field
Pulsating magnetic flux
Relative rotation between field and armature
All above
Q.24
Welding generator will have
Lap winding
Wave winding
Delta winding
Duplex wave winding
Q.25
In D.C. generators the pole shoes are fastened to the pole core by
Rivets
Counter sunk screws
Brazing
Welding
Q.26
Which generator would you prefer for feeding long D.C. transmission lines?
Series generator
Shunt generator
Over compound generator
Flat compound generator
Q.27
If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
Demagnetization only
Cross magnetization as well as magnetization
Cross-magnetization as well as demagnetizing
Cross magnetization only
Q.28
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
270 V
267.5 V
265 V
257.4 V
Q.29
Which of the following generator will have negligible terminal voltage while running on no-load?
Series generator
Shunt generator
Compound generator
Separately excited generator
Q.30
To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
just ahead of magnetic neutral axis
in magnetic neutral axis
just behind the magnetic neutral axis
0 h : 0 m : 1 s
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