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Electrical Engineering
Transformers
Quiz 2
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Q.1
When secondary of a current transformer is open-circuited its iron core will be
hot because of heavy iron losses taking place in it due to high flux density
hot because primary will carry heavy current
cool as there is no secondary current
none of above will happen
Q.2
Which of the following does not change in an ordinary transformer?
Frequency
Voltage
Current
Any of the above
Q.3
When a given transformer is run at its rated voltage but reduced frequency, its
flux density remains unaffected
iron losses are reduced
core flux density is reduced
core flux density is increased
Q.4
Which of the following does not change in a transformer?
Current
Voltage
Frequency
All of the above
Q.5
In the transformer following winding has got more cross-sectional area
Low voltage winding
High voltage winding
Primary winding
Secondary winding
Q.6
The transformer laminations are insulated from each other by
mica strip
thin coat of varnish
paper
any of the above
Q.7
Buchholz's relay gives warning and protection against
electrical fault inside the transformer itself
electrical fault outside the transformer in outgoing feeder
for both outside and inside faults
none of the above
Q.8
The efficiency of two identical transformers under load conditions can be determined by
short-circuit test
back-to-back test
open circuit test
any of the above
Q.9
For a transformer, operating at constant load current, maximum efficiency will occur at
0.8 leading power factor
0.8 lagging power factor
zero power factor
unity power factor
Q.10
The core used in high frequency transformer is usually
copper core
cost iron core
air core
mild steel core
Q.11
A transformer transforms
voltage
current
power
frequency
Q.12
The secondary winding of which of the following transformers is always kept closed?
Step-up transformer
Step-down transformer
Potential transformer
Current transformer
Q.13
If a transformer is switched on to a voltage more than the rated voltage
its power factor will deteriorate
its power factor will increase
its power factor will remain unaffected
its power factor will be zero
Q.14
In case of a double cage induction motor, the inner cage has
high inductance arid low resistance
low inductance and high resistance
low inductance and low resistance
high inductance and high resistance
Q.15
If the supply frequency to the transformer is increased, the iron loss will
not change
decrease
increase
any of the above
Q.16
In a transformer the resistance between its primary and secondary should be
zero
10 Q
1000 Q
infinity
Q.17
Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds
50°C
80°C
100°C
150°C
Q.18
The value of flux involved m the e.m.f. equation of a transformer is
average value
r.m.s. value
maximum value
instantaneous value
Q.19
In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are
friction and windage losses
copper losses
hysteresis and eddy current losses
none of the above
Q.20
Helical coils can be used on
low voltage side of high kVA transformers
high frequency transformers
high voltage side of small capacity transformers
high voltage side of high kVA rating transformers
Q.21
In a transformer the resistance between its primary and secondary is
zero
1 ohm
1000 ohms
infinite
Q.22
A transformer can have regulation closer to zero
on full-load
on overload
on leading power factor
on zero power factor
Q.23
Power transformers are designed to have maximum efficiency at
nearly full load
70% full load
50% full load
no load
Q.24
The transformer oil should have _____ volatility and _____ viscosity.
low,low
high,high
low,high
high,low
Q.25
The degree of mechanical vibrations produced by the laminations of a transformer depends on
tightness of clamping
gauge of laminations
size of laminations
all of the above
Q.26
The term 'cogging' is associated with
three phase transformers
compound generators
series motors
induction motors
Q.27
For given applied voltage, with the increase in frequency of the applied voltage
eddy current loss will decrease
eddy current loss will increase
eddy current loss will remain unchanged
none of the above
Q.28
In an actual transformer the iron loss remains practically constant from noload to fullload because
value of transformation ratio remains constant
permeability of transformer core remains constant
core flux remains practically constant
primary voltage remains constant
Q.29
The changes in volume of transformer cooling oil due to variation of atmospheric tem-perature during day and night is taken care of by which part of transformer
Conservator
Breather
Bushings
Buchholz relay
Q.30
Star/star transformers work satisfactorily when
load is unbalanced only
load is balanced only
on balanced as well as unbalanced loads
none of the above
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