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Quiz 8
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Q.1
In a D.C. machine, the value of peripheral speed should not, normally, exceed
10 m/s
20 m/s
30 m/s
40 m/s
Q.2
In a D.C. machine the current per brush arm should not be more than
100 A
200 A
300 A
400 A
Q.3
In a D.C. machine the number of brush arms is _____ the number of poles.
less than
equal to
greater than
none of the above
Q.4
The weight of copper of both armature and field windings decreases with _____ innumber of poles.
increase
decrease
either of the above
none of the above
Q.5
Which of the following problem arises in D.C. motors which are fed from thyristorbridge circuits ?
Increased I R losses
Increased core losses
Poor commutation
All of the above
Q.6
________ is the common method of applying brushes to the commntator.
Radial
Trailing
Reaction
All of the above
Q.7
Which of the following brushes can be used for high values of current density ?
Metal graphite brushes
Hard carbon brushes
Electro-graphitic brushes
Natural graphite brushes
Q.8
______ brushes are fragile and cause excessive wear of commutator,
Natural graphite
Hard carbon
Electro graphitic
Metal graphite
Q.9
The laminations of the armature of a D.C. machine are usually _____ thick.
0.1 to 0.2 mm
0.2 to 0.3 mm
0.3 to 0.4 mm
0.4 to 0.5 mm
Q.10
A practical formula for determining the thickness of insulation between low voltageand high voltage windings is
1 + 0.2 kVmm
2 + 0.5 kVmm
4 + 0.7 kV mm
5 + 0.9 kV mm
Q.11
Dummy coil should not be used in
small machines
large machines
either (a) or (b)
none of the above
Q.12
Power transformers have rating
equal to 50 kVA
equal to 100 kVA
above 200 kVA
none of the above
Q.13
Power transformers should be designed to have maximum efficiency
at one-fourth load
at one-half load
at or near full load
any of the above
Q.14
In transformers using hot rolled steel, the cross-section of the yoke is made about _____ greater than that of the core
5 percent
10 percent
15 percent
30 percent
Q.15
Yokes with rectangular cross-section are used for
small capacity transformers
medium capacity transformers
large capacity transformers
any of the above
Q.16
The cold rolled grain oriented steel has ______ permeability in the direction of thegrain orientation.
minimum
maximum
nil
none of the above
Q.17
Cylindrical windings using circular conductors, employed in transformers, are
single layered
double layered
multi-layered
none of the above
Q.18
Helical windings are used in
distribution transformers
power transformers
shell type transformers
none of the above
Q.19
Multi-layer helical windings are commonly used in the transformers as high voltagewindings
upto 20 kV
upto 50 kV
upto 80 kV
for 110 kV and above
Q.20
Disc windings are primarily used in
short capacity transformers
medium capacity transformers
high capacity transformers
any of the above
Q.21
The heat dissipating capability of transformers of ratings higher thankVA inincreased by providing which of the following ?
Corrugations
Fins
Tubes
All of the above
Q.22
Transformers with a capacity of upto _____ have a cooling radiator system with naturalcooling
2 MVA
5 MVA
7.5 MVA
10 MVA
Q.23
The forced oil and air circulation method is usual one for transformers of capacities
upto 5 MVA
upto 10 MVA
upto 20 MVA
30 MVA upwards
Q.24
The flash point of transformer oil should be higher than
40°C
60°C
80°C
104°C
Q.25
D.C. windings are
sometimes 2-layer type
never 2-layer type
always 2-layer type
none of the above
Q.26
The stator of a D.C. machine comprises of
main poles
interpoles
frame
all of the above
Q.27
D.C. servomotors are used in
purely control systems
purely A control systems
both and A control systems
none of the above
Q.28
Which of the following in an application of D.C. motors?
Traction
Drives for process industry
Battery driven vehicles
All of the above
Q.29
The surge phenomenon is particularly important in case of
low voltage transformers
medium voltage transformers
high voltage transformers
any of the above
Q.30
The cylindrical windings using circular conductors are used for current rating of
upto 20 A
upto 40 A
upto 60 A
upto 80 A
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