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1. The basic function of a transformer is to change
(A) The level of the voltage
(B) The power level
(C) The power factor
(D) The frequency
2. In an ordinary transformer which of the following does not change
(A) Voltage
(B) Current
(C) Frequency
(D) All of the above
3. The efficiency of a power transformer is around
(A) 50%
(B) 60%
(C) 80%
(D) 95%
4. In a transformer, electrical power is transferred from primary to secondary
(A) Through air
(B) By magnetic flux
(C) Through insulating medium
(D) None of
these
5. The two winding of a transformer are
(A) Conductively linked
(B) Inductively linked
(C) Not linked at all
(D) Electrically linked
6. Transformer action requires a
(A) Constant magnetic flux
(B) Increasing magnetic flux
(C) Alternating magnetic flux
(D) Alternating electrical flux
7. The flux created by the current flowing through the primary winding induced EMF is
(A) Primary winding only
(B) Secondary winding only
(C) Transformer core only
(D) Both primary and secondary winding
8. The primary and secondary winding of a power transformer always have
(A) A common magnetic circuit
(B) Separate magnetic circuit
(C) Wire of same size
(D) Same number of turns
9. The iron core in a transformer provides a ___________path to the main flux
(A) Low reluctance
(B) High reluctance
(C) Low resistance
(D) High conductivity
10. If rated DC voltage is applied instead of AC to the primary of a transformer
(A) Secondary of transformer will burn
(B) Primary of transformer will burn
(C) Secondary voltage will be excessively high (D) There will be no secondary voltage
11. A transformer transforms
(A) Voltage
(B) Current
(C) Voltage and current
(D) Frequency
12. For an ideal transformer the winding should have
(A) Maximum resistance on primary side and least resistance on secondary side
(B) Least resistance on primary side and maximum resistance on secondary side
(C) Equal resistance on primary and secondary side
(D) No ohmic resistance on either side
13. The core flux in transformer depends mainly on
(A) Supply voltage
(B) Supply voltage and frequency
(C) Supply voltage , frequency and load
(D) Supply voltage and load but independent on
frequency
14. When voltage is transformed from primary to secondary then it is _________
(A) Multiplied by K2
(B) Multiplied by K
(C) Divide by K2
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(D) Divide by K
15. A transformer step up the voltage by a factor 100. The ratio of current in the primary to that in
the secondary is
(A) 1
(B) 100
(C) 0.01
(D) 0.1
16. If the applied voltage to a transformer primary is increased by keeping the V/f ratio fixed, then
the magnetizing current and the core loss will, respectively
(A) Decrease and remain the same
(B) Increase and decrease
(C) Both remain the same
(D) Remain the same and increase
17. The applied voltage of a certain transformer is increased by 75%.while the frequency of the
applied voltage is reduced by 25%. The maximum core flux density will
(A) Increase by seven time
(B) Increase by three time
(C) Reduced to one quarter
(D) Remain the same
18. The low voltage winding of a 400/230 V single phase 50 HZ transformer is to be connected to a
25 HZ supply. In order to keep the magnetization current at the same level in both the cases the
voltage at 25 HZ should be
(A) 230 V
(B) 460 V
(C) 115 V
(D) 65 V
19. A single phase transformer rated for 220/240 V, 50 HZ operates at no load at 220 V, 40 HZ. This
frequency operation at rated voltage results in which one of the following?
(A) Increase of both eddy-current and hysteresis losses.
(B) Reduction of both eddy-current and hysteresis losses.
(C) Reduction of hysteresis loss and increase in eddy-current losses.
(D) Increase of hysteresis loss and no change in the eddy-current losses.
20. A single phase transformer when supplied from 220 V, 50 HZ has eddy current loss of 50 W. if the
transformer is connected to a voltage of 330 V, 50 HZ, the eddy current loss will be
(A) 168.75 W
(B) 112.5 W
(C) 75 W
(D) 50 W
21. 1 KVA, 230 V, 50 HZ, single phase transformer has an eddy current loss of 30 watts. The eddy
current loss when the transformer is excited by a DC source of same voltage will be
(A) 30 W
(B) More than 30 W
(C) Less than 30 W
(D) Zero Watt
22. At 50 HZ operation, a single phase transformer has hysteresis loss of 200 W and eddy current
loss of 100 W. its core loss at 60 HZ operation will be
(A) 432 W
(B) 408 W
(C) 384 W
(D) 360 W
23. Can a 50 HZ transformer be used for 25 HZ, if the input voltage is maintained constant at the
rated value corresponding to 50 HZ?
(A) Yes, since the voltage is constant current level will not change
(B) No, flux will be doubled which will drive the core to excessive saturation
(C) No, owing to decrease resistance of transformer, input current will be doubled at the load.
(D) Yes, at constant voltage, insulation will not be overstressed
24. On no load phasor diagram of transformer, the core loss component of the current remain in
phase with
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(A) No load current
(B) Primary supply voltage
(C) Core flux
(D) Primary induced voltage
25. If a sinusoidal voltage source is connected to a power transformer, its no load current will be
(A) Sinusoidal and lagging the voltage by 90°
(B) Sinusoidal and lagging the voltage by less than 90°
(C) Rich in third harmonic and its fundamental would lag the voltage by 90°
(D) Rich in third harmonic and its fundamental would lag the voltage by less than 90°
26. The transformer exciting current has two components, magnetizing component and core loss
component. Neglecting impedance drop
(A) Both of them are in phase with the supply voltage
(B) The former lags the supply voltage by 90° while the latter is in phase with supply voltage
(C) Both of them lag the supply voltage by 90°
(D) The former is in phase with the supply voltage while the latter lag the supply voltage by 90°
27. A single phase transformer has a turn’s ratio of 1:2 and is connected to a purely resistive load as
shown in the figure. The magnetizing current drown is 1 A, and the secondary currents is 1 A. if core
losses and leakage reactance are neglected, the primary current is
(A) 1.41 A
(B) 2 A
(C) 2.24 A
(D) 3 A
28. At which condition of the transformer the equivalent circuit will be as shown in the figure
(A) Under short circuit
(B) under rated load
(C) under open circuit
(D) under load and no load
29. At which condition of the transformer the equivalent circuit will be as shown in the figure
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(A) Under short circuit
(B) under rated load
(C) under open circuit
(D) under load and no load
30. In a transformer, the exciting current will be in phase quadrature with the impressed voltage
provided
(A) Only the leakage impendence drop
(B) Only the core loss is ignored
(C) Both the leakage impendence drop and the core loss are ignored
(D)Only the no load copper loss is ignored
31. The power factor of a power transformer on no load will be about
(A) Unity
(B) 0.75
(C) 0.5
(D) 0.35
32.The power factor of a transformer on no load is poor due to
(A) Magnetizing reactance of the transformer
(B) Open circuited secondary
(C) Low primary winding resistance
(D) Low no load current
33. If in a transformer core, a material having high reluctance path but having same
hysteresis loop is employed
(A) I e will increase
(B) I m will increase
(C) I m will decrease
(D) both I m and I e will increase
34. Primary winding of a transformer comprise of two identical winding in parallel. If one
winding is removed, magnetizing current will be
(A) Halved
(B) the same
(C) doubled
(D) increased four time
35. The core flux of a practical transformer with a resistance load
(A) Is strictly constant with load change
(B) Increase linearly with load
(C) Increase as the square root of the load
(D) Decrease with increase of load
36. The inductive reactance of a transformer depends on
(A) Electromotive force
(B) magneto motive force
(C) magnetic flux
(D) leakage flux
37. The flux in transformer core
(A) Increase with load
(B) decrease with load
(C) remains constant
irrespective of load
(D) none of the above
38. The mutual flux in a loaded transformer can be varied by varying
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(A) Primary current
(B) load impendence
(C) secondary current
(D) reluctance of the magnetic path
39. The primary ampere turns are counter balanced by
(A) Secondary ampere turns (B) primary flux
(C) increase in mutual flux
(D) increase in secondary current
40. In a transformer _________ decrease with the increase in leakage flux
(A) Primary induced EMF
(B)secondary induced EMF
(C) secondary terminal voltage
(D) none of the above
41. Power transformed from primary to secondary depends upon
(A) Number of primary turns
(B) number of secondary turns
(C) current transformation ratio
(D) magnetic coupling between
primary and secondary windings
42. A transformer is supplying pure resistive (unity pf) load. The power factor on primary
side will be
(A) About 0.95 (lead)
(B) About 0.95 (lag)
(C) zero
(D) unity
43. In a transformer supplying inductive load
(A) The secondary current result in equivalent primary current in phase opposition
(B) The secondary terminal voltage is less than the secondary induced EMF
(C) The power factor on primary side will be lower than that of load
(D) All of the above
44. The phasor diagram of a transformer on load can be drawn only if we know
(A) Equivalent circuit parameters of the transformer
(B) Load current
(C) load p f
(D) all of the above
45. When a transformer is operating on no load , the primary applied voltage is
approximately balanced by
(A) Primary induced EMF
(B) Secondary induced EMF
(C) Terminal voltage across the secondary
(D) Voltage drop across the resistance and reactance
46. Consider the circuit shown in given figure. For maximum power transfer to the load, the
primary to secondary turn ratio must be
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(A) 9:1
(B) 3:1
(C) 1:3
(D) 1:9
47. In the transformer circuit mode, the core loss is represented as a
(A) Series resistance
(B) series inductance
(C) shunt resistance
(D) shunt inductance
48. Full load voltage regulation of a power transformer is zero when power factor of the
load is near
(A) Unity and leading
(B) zero and leading
(C) zero and lagging
(D) unity and lagging
49. In a transformer, zero voltage regulation at full load is
(A) Not possible
(B) Possible at leading power factor load
(C) Possible at lagging power factor load
(D) Possible at unity power factor load
50. Positive voltage regulation is an indication of ___________ load
(A) Inductive
capacitive
(B) capacitive
(D) pure resistive
(C) either inductive or
51. The looses in a transformer are
(i)
(ii)
(iii)
Copper losses
Eddy current loss
Hysteresis loss
The constant power loss of a transformer is given by
(A) (i) only
(B) (i) and (ii) only
(C) (ii) and (iii) only
(D) (i) , (ii) and (iii)
52. In a power transformer iron losses remain practically constant from no load to full load.
This is because
(A) Core flux remains constant
(B) Leakage flux remains constant
(C) Both (A) and (B)
(D) neither (A) nor (B)
53. In a power transformer, if in place of sinusoidal wave, a peaked wave voltage is fed to
the primary
(A) Copper looses will be less
(B) Noise level will be reduced
(C) Iron looses will be more
(D) Iron looses will be less
54. On which of the following factors does hysteresis loss dependent?
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(i)
Flux density
(ii) frequency
(iii) thickness or
laminations
(iv) time
Select the correct answer using the code given below
(A) (ii) and (iii)
(B) (i) and (ii)
(C) (iii) and (iv)
(D) (i) and (iv)
55. The full load copper loss and iron loss of a transformer are 6,400 W and 5,000 W
respectively. The copper loss and iron loss at half load will be , respectively
(A) 3,200 W and 2,500 W
(B) 3,200 W and 5,200 W
(C) 1,600 W and 1,250 W
(D) 1,600 W and 5,000 W
56. If the frequency of input voltage of a transformer is increased keeping the magnitude of
voltage unchanged, then
(A) Both hysteresis loss and eddy current loss in the core increase
(B) hysteresis loss will increase but eddy current loss will decrease
(C) hysteresis loss will decrease but eddy current loss will increase
(D) hysteresis loss will decrease but eddy current loss will remain unchanged
57. The total iron loss in a transformer core at normal flux density was measured at 25 HZ
and 50 HZ and was found to be 250 W and 800 W respectively. The hysteresis loss at 50 HZ
would be
(A) 100 W
(B) 150 W
(C) 200 W
(D) 600 W
58. The main purpose of performing open circuit on a transformer is to measured is
(A) Copper loss
(B) core loss
(C) total loss
(D) insulation
resistance
59. Open circuit test in a transformer is performed with
(A) Rated transformer voltage
(B) Rated transformer current
(C) Direct current
(D) High frequency supply
60. The open circuit test in a transformer is usually performed by exciting the low voltage
winding. This is because
(A) It draws sufficiently large no load current which can be conversely measured
(B) The required power input is low
(C) It is not advisable to work on high voltage side
(D) The voltage required is low
61. The Open circuit test in a transformer gives
(A) Equivalent resistance and leakage resistance
(B) Magnetizing current and core loss at rated voltage
(C) Copper looses
(D) both (B) and (C)
62. In transformers, which of the following statements is valid?
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(A) In an open circuit test, copper looses and obtained while in short circuit test, core looses
are obtained
(B) In an open circuit test, current is drawn at high power factor
(C) In a short circuit, current is drawn at zero power factor
(D) In an open circuit test, current is drawn at low power factor
63. A 10 KVA, 400 V/200 V single phase transformer with 10% impendence draws a steady
short circuit line current of
(A) 50 A
(B) 150 A
(C) 250 A
(D) 350 A
64. While performing the open circuit and short circuit test on a transformer to determine
parameters the status of the low voltage (LV) and high voltage (HV) winding will be such that
(A) In OC,LV is open and in SC HV is shorted
(B) In OC, HV is open and in SC LV is shorted
(C) In OC,LV is open and in SC LV is shorted
(D) In OC,LV is open and in SC HV is shorted
65. For a transformer to be tested at full load condition but consuming only looses from the
mains, we do
(A) Load test
(B) Open circuit and short circuit tests
(C) Back to back test
(D) None of the above
66. The efficiency of two identical transformer under load condition can be determined by
(A) Back to back test
(B) open circuit test
(C) short circuit test
(D) any of the above
67. Two transformers, each having iron loss of P I watts and full load copper loss of P c , are
put to back to back test and full load current is allowed to flow through the secondary’s, the
total input will be
(A) 2Pi
(B) 2Pc
(C) Pi + Pc
(D) 2(Pi + Pc)
68. The efficiency of a power transformer can be determined indirectly by
(A) Open circuit test alone
(B) Short circuit test alone
(C) Open circuit and short circuit test
(D) Back to back test
69. The transformer efficiency at relatively light loads is quite low this is due to
(A) Small copper looses
(B) Small secondary output
(C) High fixed loss in comparison to the output
(D) Poor power factor
70. The transformer efficiency, under heavy loads, is comparatively low due to
(A) Large increase in copper losses in comparison to the output
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(B) Large increase in iron losses
(C) Drop in power factor
(D) None of the above
71. The full load copper loss and iron loss of a transformer are 6400 W and 500 W,
respectively. The above copper loss and iron loss at half load will be
(A) 3200 W and 250 W respectively
(B) 3200 W and 500 W respectively
(C) 1600 W and 125 W respectively
(D) 1600 W and 500 W respectively
72. The efficiency of a 100 KVA transformer is 0.98 at full as well as half load. For this
transformer at full load the copper loss
(A) Is less then core loss
(B) Is equal to core loss
(C) Is more than core loss
(D) None of the above
73. Transformer will operate at maximum efficiency when
(A) Hysteresis loss = eddy current loss
(B) Eddy current loss = copper loss
(C) Copper loss = iron loss
(D) Hysteresis loss = copper loss
74. Power transformer designed to have maximum efficiency around _______ full load
(A) Nearly
(B) 70% of
(C) 50% of
(D) 25% of
75.The transformer efficiency will be maximum of a power factor of
(A) 0.8 lead
(B) unity
(C) 0.8 lag
(D) 0.5 lag or lead
76. If P c and P sc represent core and full load ohmic losses respectively. The maximum KVA
delivered to load corresponding to maximum efficiency is equal to rated KVA multiplied by
(A) P c / P sc
(B) √ P c / P sc
(C) (P c / P sc)2
(D)( P sc / P c)2
77. If P1 and P2 be the iron and copper losses of a transformer at full load and the maximum
efficiency is at 75% of the full load, than what is the ratio of P1 and P2
(A) 9/16
(B) 10/16
(C) ¾
(D) 3/16
78. What is load at which maximum efficiency occurs in case of a 100 KVA transformer with
iron loss of 1 KW and full load copper loss of 2 KW?
(A) 100 KVA
(B) 70.7 KVA
(C) 50.5 KVA
(D) 25.2 KVA
79. A 500 KVA transformer has constant loss of 500 W and cooper looses at full load are
2000 W. then at what load, is the efficiency maximum
(A) 250 KVA
(B) 500 KVA
(C) 1000 KVA
(D) 125 KVA
80. A 2 KVA transformer has iron loss of 150 W and full load copper loss of 250 W. the
maximum efficiency of the transformer would occur when the total loss is
(A) 500 W
(B) 400 W
(C) 300 W
(D) 275 W
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81. If Pi be the iron loss and Pc be the copper loss on full load, then which of the following
condition had to be satisfied to obtained maximum efficiency at ¾ full load
(A) Pc = 3 Pi /4
(B) Pc = 4Pi /3
(C) Pc = 16 Pi /9
(D) Pc = 9Pi /16
82. A single phase transformer has a maximum efficiency of 90% at full load and unity power
factor. Efficiency at half load at the same power factor is
(A) 86.7%
(B) 88.26%
(C) 88.9%
(D) 87.8%
83. The all day efficiency of a distribution transformer will be high with low
(A) Copper losses
(B) Iron losses
(C) Operating temperature
(D) Copper as well as iron losses
84. The all day efficiency of a transformer depends primarily on
(A) Its copper loss
(B) The amount of load
(C) The duration of load
(D) Both (B) and (C)
85. The desirable properties of transformer core material are
(A) Low permeability and low hysteresis loss
(B) High permeability and high hysteresis loss
(C) High permeability and low hysteresis loss
(D) Low permeability and high hysteresis loss
86. The use of higher flux density in the transformer design
(A) Reduces the weight per KVA
(B) Increase the weight per KVA
(C) Has no relation with the weight of transformer
(D) Increase the weight per KW
87. What does the use of higher flux density value in a transformer design lead to
(A) Increase in weight per KVA
(B) Decrease in weight per KVA
(C) Reduced iron looses
(D) Reduced copper looses
88. The size of the transformer core depends upon
(A) Frequency
(B) permissible flux density in the core material.
(C) area of the core
(D) both (A) and (B)
89. Ferrite cores are employed in high frequency transformer due to their
(A) Low resistance
(B) high resistance
(C) low permeability
(D) high hysteresis loss
90. Cores of large power transformers are made from which one of the following
(A) Hot-rolled steel
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(B) Cold-rolled non grain oriented steel
(C) Cold-rolled grain oriented steel
(D) Ferrite
91. Grain oriented laminated sheet steel in transformer reduces
(A) Copper loss
(B) eddy current loss
(C) hysteresis loss
(D) none of the above
92. Which of the following will improve the mutual coupling between primary and secondary
circuits?
(A) Transformer oil of high breakdown voltage
(B) High reluctance magnetic core
(C) Winding material of high resistivity
(D) Low reluctance magnetic core
93. In order the reduce the hysteresis loss
(A) Core may be laminated
(B) Silicon steel may be used as the core material
(C) Core may be constructed with any permanent magnet material such as Alnico
(D) Core may be impregnated with varnish
94. Why is the core of the transformer built up of laminations?
(A) To reduce eddy current loss
(B) For convenience of fabrication
(C) No specific advantage
(D) For increase the permeability
95. When are eddy current losses in a transformer reduced?
(A) If lamination are thick
(B) If the number of turns in primary winding is reduced
(C) If the number of turns in secondary winding is reduced
(D) If lamination are thin
96. The yoke section of transformers are coated with an enamel layer in order to
(A) Reduce hum
(B) Attain adhesion between lamination
(C) Insulate laminations from each other
(D) Prevent corrosion of the laminations
97. The joint in the transformer core laminations are staggered so as to
(A) Avoid continues gap causing increase in magnetizing current
(B) Increase the mechanical strength of the assembled core
(C) Avoid under humming noise
(D) Facilitate assembly of core after putting performed coils on the core
(E) All of the above
98. For CRGOS mitred overlap is preferred for the core yoke joints as it
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(A) Reduces the magnetizing current and also the core losses.
(B) Improves the mechanical strength
(C) Reduce magnetostriction.
(D) Makes better use of core space
99. The degree of mechanical vibrations caused by core laminations in a transformer
depends on
(A) Size of laminations
(B) Gauge of laminations
(C) Tightness of laminations
(D) All of the above
100. The noise, in a transformer caused by vibration of laminations set by magnetic forces, is
termed as
(A) Zoom
(B) hum
(C) buzz
(D) none of these
101. The primary and secondary winding are interlaced for
(A) Easiness of coil making
(B) reduced leaking reactance
(C) reduced cost
(D) uniform heating
102. The leakage flux of primary and secondary winding can be reduced to the maximum by
(A) Winding primary and secondary coils on separate limbs
(B) Winding primary and secondary coils one upon the other coaxially
(C) Increasing the number of turns
(D) Employing low permeability magnetic material core
103. The concentric winding are used in core type transformers with ___________winding
placed next to the core
(A) Lv
(B) primary
(C) hv
(D) secondary
104. Low voltage winding are placed next to the core in the case of concentric windings as in
this case_________ is/are reduced
(A) Hysteresis loss
(B) leakage fluxes
(C) eddy current loss
(D) copper loss
(E) insulation requirement
105. In a power transformer
(A) Primary winding is always wound with many turns of thin wire
(B) Secondary winding is always wound with lesser number of turns of thin wire
(C) Low voltage winding is always wound with lesser number of turns of thicker wire
(D) High voltage winding is always wound with larger number of turns of thicker wire
106. In transformer, the primary and secondary are interlaced so that
(A) There may be maximum flux linkage between the two windings
(B) Copper is saved
(C) both (A) and (B)
(D) statement is false
107. In a large capacity transformer, 5% of the turns at the end of hv winding are provided
with extra insulation so as to provide protection
(A) Against corona
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(B) against lighting
(C) due to surges occurring during switching operations
(D) all of the above
108. When a transformer winding suffers a short circuit, the adjoining turn of the same
winding experienced
(A) An attractive force
(B) a repulsive force
(C) no force
109. Under short circuit condition, the winding of a transformer having 5% impendence will
experience a redial force
(A) 5 time of full load value
(B) 20 time of full load value
(C) 25 time of full load value
(D) 400 time of full load value
110. Major insulation in a transformer is the insulation between the
(A) 1 v winding and core
(B) 1 v and hv windings
(C) Turns of the winding turns
(D) Both (A) and (B)
111. Minor insulation in a transformer is the insulation between the
(A) 1 v winding and core
(B) 1 v and hv windings
(C) Turns of the winding
(D) Layers of the winding
(E) Both (C) and (D)
112. In a transformer, an insulating material may fail due to
(A) Moisture
(B) dust
(C) voids in the winding
(D) any one or more of the above
113. The function of oil in a transformer is
(A) To provide insulation and cooling
(B) To provide protection against lightning
(C) To provide protection against short circuit
(D) To provide lubrication
114. The color of fresh dielectric oil used in transformer is
(A) Dark brown
(B) pale yellow
(C) pale pink
(D) white grey
115. The transformer oil should have
(A) Low volatility
(B) high dielectric strength
(C) good resistance to emulsion with water
(D) low viscosity to provide good heat transformer
(E) all of the above
116. Transformer oil must be free from
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(A) Moisture
(B) sludge
(C) gases
(D) sulphur
117. The core and winding of a transformer are put in a steel tank in order to
(A) Make it suitable for outdoor operation
(B) Provide protection against mechanical damages and provide additional cooling
(C) Improve its appearance
(D) All of the above
118. Conservator (for transformer ) is used
(A) To take up the expansion of oil due to temperature rise
(B) To act as an oil storage
(C) For better cooling of transformer
(D) None of the above
119. Sludge formation in transformer oil is due to which one of the following?
(A) Ingress of dust particles and moisture in the oil
(B) Appearance of small fragment of paper, varnish cotton and other organic materials in
the oil.
(C) Chemical reaction of transformer oil with the insulating materials
(D) Oxidation of transformer oil.
120. In a power transformer, the breather is provided in order to
(A) Filter transformer oil
(B) Prevent ingress of moisture with air
(C) Provide oxygen to the cooling oil
(D) Provide fresh air increasing cooling effect.
121. The chemical used in breather of transformer should have the quality of
(A) Absorbing moisture
(B) Ionizing air
(C) Cleansing the transformer oil
(D) None of the above
122. Malfunctioning of the Buchholz relay may be caused due to
(A) Heavy external short circuit
(B) Improper breather action
(C) Dropping of oil level below the relay level during operation
(D) Excessive overheating
123. A Buchholz relay is used for
(A) Protection of a transformer against all internal faults
(B) Protection of a transformer against external faults
(C) Protection of a transformer against both internal and external faults
(D) Protection of induction motor
124. Which is the arrangement of winding in a core type single phase transformer?
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(A) Half lv inside and half hv outside on each core limb
(B) Lv on one core limb and hv on the other
(C) Sandwiched lv and hv discs on each core limb
(D) Half hv inside and hv outside on each core limb
125. For core type power transformer, both primary and secondary winding have circular
coil sections, as it
(A) Reduced core material requirement and so also reduces the core loss
(B) Gives the strongest mechanical shape
(C) Is easier to wind
(D) Reduced the copper requirement.
126. With stepping in construction of transformer core
(A) Copper losses are reduced
(B) Copper is saved
(C) High flux density can be achieved
(D) Mechanical strength to the core is improved
(E) Both (A) and (B)
127. A shall type transformer is commonly used at it has
(A) Two magnetic path
(B) Reduced magnetic flux leakage
(C) Reduced copper losses
(D) Both (A) and (B)
128. Spiral core transformer, in which core is made up of steel strip has the advantage(s) of
(A) Minimum looses
(B) lighter construction
(C) lesser weight
(D) all of these
129. Distribution transformer have core losses
(A) > copper losses
(B) < copper losses
(C) = copper loss
(D) = ½ (copper losses)
130. Distribution transformer are designed to have maximum efficiency nearly at _________
of full load
(A) 100%
(B) 70%
(C) 25%
(D) 10%
131. A distribution transformer is selected on the basis of
(A) Voltage regulation
(B) efficiency (C) all day efficiency
(D) none of these
132. The distribution transformers are designed with minimum possible iron losses. This is
because
(A) The primary of a distribution transformer is energized for all the 24 hours
(B) Iron losses will cause undue heating
(C) The iron losses may cause damage to the insulation
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(D) None of the above
133. Which part of transformer is subjected to maximum heating
(A) Frame
(B) core
(C) winding
(D) oil
134. Which of the following method is employed for cooling of power transformers of rating
not exceeding 10 MVA?
(A) Air blast cooling
(B) natural oil cooling
(C) forced oil cooling
(D) natural air cooling
135. Transformer are rated in KVA instead of KW because
(A) Load PF is often not known.
(B) KVA is fixed where KW depends on load PF.
(C) Total transformer load depends on volt-ampere
(D) It has become customary
136. Two 3-limb phase delta-star connected transformers are supplied from the same
source. One of the transformers is Dy1 and the other is Dy11 connection. The phase
difference between the corresponding phase voltage of the secondary’s would be
(A) 0°
(B) 30°
(C) 60°
(D) 120°
137. Which there phase connection can be used in a transformer to introduce a phase
difference of 30° between its output and corresponding input line voltage?
(A) Star-star
(B) star-delta
(C) delta-delta
(D) delta-zigzag
138. Three single phase transformers are connected to form 3-phase transformer bank. The
transformer are connected in the following manner
The transformer connection will be represented by
(A)
Yd0
(B) Yd1
(C) Yd6
(D) Yd11
139. Which of the following connection of transformer will give the highest secondary
voltage?
(A) Delta primary, delta secondary
(B) Delta primary , star secondary
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(C) Star primary, star secondary
(D) Star primary, delta secondary
140. Transformer core lamination are coated with an enamel layer in order to
(A) Reduce hum
(B) attain adhesion between laminations
(C) insulate laminations from each other
(D) prevent corrosion of the laminations
ANSWER KEY:1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
(A)
(C)
(D)
(B)
(B)
(C)
(D)
(A)
(A)
(B)
(C)
(D)
(B)
(B)
(B)
(D)
(B)
(C)
(D)
(B)
(D)
(C)
(B)
45. (A)
46. (B)
47. (C)
48. (A)
49. (B)
50. (C)
51. (C)
52. (A)
53. (D)
54. (B)
55. (D)
56. (D)
57. (C)
58. (B)
59. (A)
60. (A)
61. (B)
62. (D)
63. (C)
64. (B)
65. (C)
66. (A)
67. (D)
89. (B)
90. (C)
91. (C)
92. (D)
93. (B)
94. (A)
95. (D)
96. (B)
97. (E)
98. (A)
99. (D)
100. (B)
101. (B)
102. (B)
103. (A)
104. (E)
105. (C)
106. (A)
107. (C)
108. (A)
109. (D)
110. (D)
111. (E)
133. (C)
134. (B)
135. (C)
136. (C)
137. (B)
138. (B)
139. (B)
140. (C)
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24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
(B)
(D)
(B)
(C)
(C)
(A)
(C)
(D)
(A)
(B)
(C)
(A)
(D)
(C)
(D)
(A)
(C)
(D)
(B)
(D)
(D)
68. (C)
69. (C)
70. (A)
71. (D)
72. (C)
73. (C)
74. (A)
75. (B)
76. (B)
77. (A)
78. (B)
79. (A)
80. (C)
81. (C)
82. (D)
83. (D)
84. (D)
85. (C)
86. (A)
87. (B)
88. (D)
112. (D)
113. (A)
114. (B)
115. (E)
116. (A)
117. (B)
118. (A)
119. (D)
120. (B)
121. (A)
122. (C)
123. (A)
124. (A)
125. (B)
126. (E)
127. (D)
128. (D)
129. (B)
130. (B)
131. (C)
132. (A)
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ENGINEERING ACADEMY DEHRADUN
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