Transformer MCQs - ELECTRICAL TECHNOLOGY4U

Transformers are the device which is capable of receiving AC power at one voltage and delivering it at another voltage. In this way transformer help in achieve better transmission efficiency, while transferring the power over longer distances with high voltages,In this article include transformer MCQs which cover the basic concept of transformer(Correct Answer is in Bold)

MCQs on Transformer

1-Magnetic flux path in a transformer should be

high resistance
high reluctance
low resistance
low reluctance

02-Due to the vibration of laminations the sound produced is termed as

magnetostrication
boo
hum
zoom

03-Hysteresis loss in a transformer varies with flux density as

Bmax
Bmax1-6
Bmax1-83
B max

04-To construct the transformer core the Material used is usually

Wood
silicon steel
copper
aluminium

05-The lamination thickness used in a transformer is usually

4 mm to 5 mm
14 mm to 15 mm
25 mm to 40 mm
0.4 mm to 0.5 mm

06-In a transformer th function of conservator is

to project against ‘internal fault
to reduce copper as well as core losses
to cool the transformer oil
to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings

07-The highest voltage which is used to transmit electrical power in Pakistan

(a) 33 kV.

(6) 66 kV

132 kV
660 kV

08-No-load on a transformer is carried out to determine

copper loss
magnetising current and loss
magnetising current
efficiency of the transformer

09-Transformer coil dielectric strength should be

12 kV
33 kV
100 kV
330 kV

10-Sumpner’s test is conducted on transformers to determine

stray losses
all-day efficiency
temperature
none of the above

11-The permissible flux density in case of cold rolled grain oriented steel is around

2.7 Wb/m2
3.7 Wb/m2
4.7 Wb/m2
1.7 Wb/m2

12-The efficiency of a transformer will be maximum when

copper losses = hysteresis losses
hysteresis losses = eddy current losses
eddy current losses = copper losses
copper losses = iron losses Ans: d

No-load current in a transformer
leads the voltage by about 75°
lags behind the voltage by about 15°
lags behind the voltage by about 75°
leads the voltage by about 15°

13-The main reason of providing an iron core in a transformer is to

provide support to windings
decrease the reluctance of the magnetic path
reduce hysteresis loss
reduce eddy current losses

14-Out of the following which is not a part of transformer ,,

Conservator
Exciter
Breather
Buchholz relay

15-During the short circuit test on a transformer which site of transformer should be short circuited

High voltage side
Low voltage side

Primary side
Secondary side

16-In the transformer which winding will have cross-sectional area

Low voltage winding
Primary winding
Secondary winding
High voltage winding

17-A transformer transforms

Voltage
power
current
frequency

18-A transformer increase and decrease the voltage of a D.C. supply because

Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero
there is no need to change the D.C. voltage
a D.C. circuit has more losses
none of the above

19-Transformer Primary winding is

is always a low voltage winding
is always a high voltage winding
could either be a low voltage or high voltage winding
none of the above

20-In a transformer which winding has more number of turns ?

Low voltage winding
Primary winding
Secondary winding
High voltage winding

21-The power transformer efficiency is of the order of

100 per cent
50 per cent
25 per cent
98 per cent

22-In a transformer the losses which remain constant irrespective of load changes are

hysteresis and eddy current losses
friction and windage losses
copper losses
none of the above

23-The common method of power transformer cooling is

natural air cooling
air blast cooling
oil cooling
any of the above

24-No load current lags applied voltage in a transformer by an angle

180°
75°
120″
90°

25-The efficiency of a transformer depends upon

supply frequency
power factor of load
load current
both (b) and (c)

26-The function of conservator in a transformer is

provide fresh air for cooling the transformer
supply cooling oil to transformer in time of need
protect the transformer from damage when oil expends due to heating
none of the above

27-Ina transformer natural oil cooling is used upto a rating of

3000 kVA
1000 kVA
500 kVA
250 kVA

28-Power transformers are designed to have maximum efficiency at

70% full load
50% full load
nearly full load
no load

29-The maximum efficiency of a distribution transformer is

at no load
at 80% full load
at full load
at 50% full load

30-Transformer breaths in when

load on it increases
load remains constant
load on it decreases
none of the above

31-No-load current of a transformer has

has small magnitude and low power factor
has high magnitude and low power factor

has high magnitude and high power factor
has small magnitude and high power factor

32-Spacers are provided between adjacent coils

to insulate the coils from each other
to provide free passage to the cooling oil
both (a) and (b)
none of the above

33-If the secondary leakage flux is greater then

less will be the primary induced e.m.f.
less will be the primary terminal voltage
less will be the secondary induced e.m.f.
none of the above

34-The main reason of providing iron core in a step-up transformer is

to decrease the magnitude of magnetizing current
to provide coupling between primary and secondary
to increase the magnitude of mutual flux
to provide all above features

35-The power transformer is a constant

main flux device
voltage device
current device
power device

36-when two transformer operating in parallel will share the load which depend upon

leakage reactance
efficiencies
ratings
per unit impedance

37-when the transformer is operating continuously ,the maximum temperature is on which part of transformer

windings
core
tank
any of the above

38-The hum in a transformer is mainly attributed to

magnetostriction
load changes
oil in the transformer

mechanical vibrations

39-The maximum load of a power transformer is limited by its

voltage ratio
temperature rise
dielectric strength of oil
copper loss

40-The efficiency of a transformer during the heavy loads is low because

iron loss is increased considerably
voltage drop both in primary and secondary becomes large
secondary output is much less as compared to primary input
copper loss becomes high in proportion to the output

41-On a transformer open circuit test is conducted to measure.

core loss
insulation resistance
copper loss
total loss
efficiency

42-A no-load test is performed on a transformer to determine

magnetising current and loss
core loss
copper loss
efficiency
magnetising current

43-The voltage transformation ratio of a transformer is equal to the ratio of

secondary induced e.m.f. to primary induced e.m.f.
primary turns to secondary turns
secondary current to primary current

secondary terminal voltage to primary applied voltage

44-which Part of the transformer will damage more during overheating

winding insulation
iron core
copper winding
frame or case
transformer tank

45-If a transformer is switched on to a voltage more than the rated voltage

its power factor will increase
its power factor will remain unaffected
its power factor will be zero
its power factor will deteriorate

46-When the transformation ratio of auto transformer is ___________ it make effective saving on copper and copper losses

less than one
great than one
approximately equal to one
none of the above

47-Minimum voltage regulation occurs when the power factor of the load is

leading
unity
lagging
zero

48-In a step-down transformer, there is a change of 20 A in the load current. This results in change of supply current of

less than 20 A
more than 20 A

10 A
none of the above

49–The efficiencies of transformers as compared to the efficiency of same rating electric motor are

about the same
much higher
somewhat smaller
none of the above

50-What will happen if the transformers which is working in parallel not connected with same polarity ?

The power factor of the two trans-formers will be different from the power factor of common load
The transformers will not share load in proportion to their kVA ratings
Incorrect polarity will result in dead short circuit

51-when the two transformer working in parallel have different percentage impedance then

transformers will be overheated
parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load
power factors of both the trans-formers will be same
parallel operation will be not possible

52-Tapping are generally provide in a transformer on ?

primary side
secondary side
low voltage side
high voltage side

53-The use of higher flux density in the transformer design

reduces iron losses
reduces weight per kVA

reduces copper losses
increases part load efficiency

54-The chemical which is used in breather for transformer should have the quality of

ionizing air
cleansing the transformer oil
cooling the transformer oil.
absorbing moisture

55-The chemical used in breather is

silica gel
asbestos fiber
silica sand
sodium chloride

56-An ideal transformer has infinite values of primary and secondary inductances. The statement is

true
false

57-The transformer ratings are usually expressed in terms of

volts
amperes
kW
kVA

58-Which of the following does not change in a transformer ?

Frequency
Current
Voltage
All of the above

59-In a transformer the energy is conveyed from primary to secondary

by the flux
through cooling coil
through air
none of the above

60-A transformer core is laminated to

reduce hysteresis loss
reduce eddy current losses
reduce copper losses
reduce all above losses

61-The degree of mechanical vibrations produced by the laminations of a transformer depends on

size of laminations
tightness of clamping
gauge of laminations
all of the above

62-The no-load current drawn by transformer is usually what percent of the full-load current ?

0.3 to 0.5 per cent
2 to 5 per cent
15 to 20 per cent
30 to 40 per cent

63-In a transformer the resistance between its primary and secondary is

zero

1 ohm
1000 ohms
infinite

64-A transformer oil must be free from

moisture
sludge
odour
gases

65-A Buchholz relay can be installed on

oil cooled transformers
auto-transformers
air-cooled transformers
welding transformers

66-Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds

150°C
40°C
70°C
100°C

67-The main reason for generation of harmonics in a transformer could be

fluctuating load
saturation of core
poor insulation
mechanical vibrations

68-Distribution transformers are generally designed for maximum efficiency around

90% load
zero load
50% load
25% load

69-Which of the following property is not required in the material for transformer core ?

High thermal conductivity
Mechanical strength
Low hysteresis loss
High permeability

70-Star/star transformers work satisfactorily when

load is unbalanced only
on balanced as well as unbalanced loads
load is balanced only
none of the above

71-Delta/star transformer works satisfactorily when

load is balanced only
load is unbalanced only
on balanced as well as unbalanced loads
none of the above

72-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

73-The magnetizing current of a transformer is usually small because it has

large leakage flux
laminated silicon steel core
fewer rotating parts
small air gap

74-Which of the following does not change in an ordinary transformer ?

Frequency
Voltage
Current
Any of the above

75-The leakage flux in a transformer depends upon

load current
load current and voltage
load current, voltage and frequency
load current, voltage, frequency and power factor

76-The path of the magnetic flux in transformer should have

high reluctance
low reactance
high resistance
low resistance

77-Noise level test in a transformer is a

special test
routine test
type test
none of the above

78-Which of the following is not a routine test on transformers ?

Core insulation voltage test
Impedance test
Radio interference test
Polarity test

79-A transformer can have zero voltage regulation at

leading power factor
lagging power factor
unity power factor
zero power factor

80-Helical coils can be used on

high frequency transformers
high voltage side of small capacity transformers
low voltage side of high kVA transformers
high voltage side of high kVA rating transformers

81-Harmonics in transformer result in

increased core losses
increased I²R losses
magnetic interference with communication circuits
all of the above

82-The core used in high frequency transformer is usually

copper core
cost iron core
mild steel core
air core

83-The full-load copper loss of a transformer is 1600 W. At half-load, the copper loss will be

(a) 6000 W

(b) 1600 W

800 W
400 W

84- The value of flux involved in the e.m.f. equation of a transformer is

average value
r.m.s. value
maximum value
instantaneous value

85-Silicon steel used in laminations mainly reduces

hysteresis loss
eddy current losses
copper losses
all of the above

86-Which winding of the transformer has less cross-sectional area ?

High voltage winding
Primary winding
Secondary winding
Low voltage winding

87-Power transformers are generally designed to have maximum efficiency around

no-load
half-load
near full-load
15 % overload

88-Which of the following is the main advantage of an auto-transformer over a two winding transformer ?

Hysteresis losses are reduced
Copper losses are negligible
Eddy losses are totally eliminated
Saving in winding material

89-During short circuit test iron losses are negligible because

the current on secondary side is negligible
the voltage on secondary side does not vary
the voltage applied on primary side is low
full-load current is not supplied to the transformer

90-Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in

short-circuiting of the secondary’s
power factor of one of the transformers is leading while that of the other lagging
transformers having higher copper losses will have negligible core losses
loading of the transformers not in proportion to their kVA ratings

91-The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer

Conservator
Breather
Bushings
Buchholz relay

92-An ideal transformer is one which has

no losses and magnetic leakage
interleaved primary and secondary windings
a common core for its primary and secondary windings
core of stainless steel and winding of pure copper metal
none of the above

93-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

94-In an actual transformer the iron loss remains practically constant from no load to full load because

value of transformation ratio remains constant
permeability of transformer core remains constant
core flux remains practically constant
primary voltage remains constant
secondary voltage remains constant

95-An ideal transformer will have maximum efficiency at a load such that

copper loss < iron loss
copper loss > iron loss
copper loss = iron loss
none of the above

96-If the supply frequency to the transformer is increased the iron loss will

not change
decrease
increase
any of the above

97-Negative voltage regulation is indicate that the load is

capacitive only
inductive only
inductive or resistive
none of the above

98-Iron loss of a transformer can be measured by

low power factor wattmeter
unity power factor wattmeter
frequency meter
any type of wattmeter

100-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

101-The transformer laminations are insulated from each other by

mica strip
thin coat of varnish
paper
any of the above

102-Which type of winding is used in 3-phase shell-type transformer ?

Circular type
Sandwich type
Cylindrical type
Rectangular type

103-During open circuit test of a transformer

primary is supplied rated voltage
primary is supplied full-load current
primary is supplied current at reduced voltage
primary is supplied rated kVA

104-Open circuit test on transformers is conducted to determine

hysteresis losses
copper losses
core losses
eddy current losses

104-Short circuit test on transformers is conducted to determine

hysteresis losses
copper losses
core losses
eddy current losses

105-For the parallel operation of single phase transformers it is necessary that they should have

same efficiency
same polarity
same kVA rating
same number of turns on the secondary side.

106-The transformer oil should have volatility and viscosity.

low,low
high,high
low,high
high,low

107-The function of breather in a transformer is

to provide oxygen inside the tank
to cool the coils during reduced load
to cool the transformer oil
to arrest flow of moisture when outside air enters the transformer

108-The secondary winding of which of the following transformers is always kept closed ?

Step-up transformer
Step-down transformer
Potential transformer
Current transformer

109-The size of a transformer core will depend on

frequency
area of the core

flux density of the core material
(a) and (b) both

110-Natural air cooling is generally restricted for transformers up to

1.5 MVA
5 MVA
15 MVA
50 MVA

111-A shell-type transformer has

high eddy current losses
reduced magnetic leakage
negligibly hysteresis losses
none of the above

112-A transformer can have regulation closer to zero

on full-load
on overload
on leading power factor
on zero power factor

113-A transformer transforms

voltage
current
current and voltage
power

114-Reduction in core losses and increase in permeability are obtained with transformer employing

core built-up of laminations of cold rolled grain oriented steel
core built-up of laminations of hot rolled sheet
either of the above
none of the above

115-In a power or distribution transformer about 10 percent end turns are heavily insulated

to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
to absorb the line surge voltage and save the winding of transformer from damage
to reflect the line surge and save the winding of a transformer from damage
none of the above

116-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

117-Losses which occur in rotating electric machines and do not occur in trans formers are

magnetic losses
hysteresis and eddy current losses
copper losses
friction and windage losses

118-In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are

hysteresis and eddy current losses
friction and windage losses
copper losses

none of the above

119- The secondary of a current transformer is always short-circuited under operating conditions because it

avoids core saturation and high voltage induction
is safe to human beings
protects the primary circuit
none of the above

120-In a transformer the resistance between its primary and secondary should be

zero
10 Q

(d)infinity

121-A good voltage regulation of a transformer means

output voltage fluctuation from no load to full load is least
output voltage fluctuation with power factor is least
difference between primary and secondary voltage is least
difference between primary and secondary voltage is maximum

122-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

123-Which of the following protection is normally not provided on small distribution transformers ?

Overfluxing protection
Buchholz relay
Overcurrent protection
All of the above

124-Which of the following acts as a protection against high voltage surges due to lightning and switching ?

Horn gaps
Thermal overload relays
Breather
Conservator

125-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

126-Which of the following insulating materials can withstand the highest temperature safely ?

Cellulose
Asbestos
Mica
Glass fibre

127-Which of the following parts of a transformer is visible from outside ?

Bushings
Core
Primary winding
Secondary winding

128-The noise produced by a transformer is termed as

zoom
hum
ringing
buzz

129-Which of the following loss in a transformer is zero even at full load ?

Core loss
Friction loss
Eddy current loss
Hysteresis loss

130-Which of the following is the most likely source of harmonics in a transformer ?

poor insulation
Overload
loose connections
Core saturation

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About The Author

hussainbalti40

I am Hussain Syed from Pakistan .i am electrical engineer by profession and working with a well reputed organization which is related to electrical technology .