• 1. 
    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
  • 2. 
    Which of the following does not change in a transformer ?

  • Current
  • Voltage
  • Frequency
  • All of the above
  • 3. 
    In a transformer the energy is conveyed from primary to secondary

  • through cooling coil
  • through air
  • by the flux
  • none of the above
  • 4. 
    A transformer core is laminated to

  • reduce hysteresis loss
  • reduce eddy current losses
  • reduce copper losses
  • reduce all above losses
  • 5. 
    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
  • 6. 
    The no-load current drawn by transformer is usually what per cent of the full-load current ?

  • 0.2 to 0.5 per cent
  • 2 to 5 per cent
  • 12 to 15 per cent
  • 20 to 30 per cent
  • 7. 
    The path of a magnetic flux in a transformer should have

  • high resistance
  • high reluctance
  • low resistance
  • low reluctance
  • 8. 
    No-load on a transformer is carried out to determine

  • copper loss
  • magnetising current
  • magnetising current and loss
  • efficiency of the transformer
  • 9. 
    The dielectric strength of transformer oil is expected to be

  • lkV
  • 33 kV
  • 100 kV
  • 330 kV
  • 10. 
    Sumpner’s test is conducted on trans-formers to determine

  • temperature
  • stray losses
  • all-day efficiency
  • none of the above
  • 11. 
    The permissible flux density in case of cold rolled grain oriented steel is around

  • 1.7 Wb/m2
  • 2.7 Wb/m2
  • 3.7 Wb/m2
  • 4.7 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
  • 13. 
    No-load current in a transformer

  • lags behind the voltage by about 75°
  • leads the voltage by about 75°
  • lags behind the voltage by about 15°
  • leads the voltage by about 15°
  • 14. 
    The purpose of providing an iron core in a transformer is to

  • provide support to windings
  • reduce hysteresis loss
  • decrease the reluctance of the magnetic path
  • reduce eddy current losses
  • 15. 
    Which of the following is not a part of transformer installation ?

  • Conservator
  • Breather
  • Buchholz relay
  • Exciter
  • 16. 
    While conducting short-circuit test on a transformer the following side is short circuited

  • High voltage side
  • Low voltage side
  • Primary side
  • Secondary side
  • 17. 
    In the transformer following winding has got more cross-sectional area

  • Low voltage winding
  • High voltage winding
  • Primary winding
  • Secondary winding
  • 18. 
    A transformer transforms

  • voltage
  • current
  • power
  • frequency
  • 19. 
    A transformer cannot raise or lower the voltage of a D.C. supply because

  • there is no need to change the D.C. voltage
  • a D.C. circuit has more losses
  • Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero
  • none of the above
  • 20. 
    Primary winding of a transformer

  • 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
  • 21. 
    Which winding in a transformer has more number of turns ?

  • Low voltage winding
  • High voltage winding
  • Primary winding
  • Secondary winding
  • 22. 
    Efficiency of a power transformer is of the order of

  • 100 per cent
  • 98 per cent
  • 50 per cent
  • 25 per cent
  • 23. 
    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
  • 24. 
    A common method of cooling a power transformer is

  • natural air cooling
  • air blast cooling
  • oil cooling
  • any of the above
  • 25. 
    The no load current in a transformer lags behind the applied voltage by an angle of about

  • 180°
  • 120″
  • 90°
  • 75°
  • 26. 
    In a transformer routine efficiency depends upon

  • supply frequency
  • load current
  • power factor of load
  • both (b) and (c)
  • 27. 
    In the transformer the function of a conservator is to

  • 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
  • 28. 
    Natural oil cooling is used for transformers up to a rating of

  • 3000 kVA
  • 1000 kVA
  • 500 kVA
  • 250 kVA
  • 29. 
    Power transformers are designed to have maximum efficiency at

  • nearly full load
  • 70% full load
  • 50% full load
  • no load
  • 30. 
    The maximum efficiency of a distribution transformer is

  • at no load
  • at 50% full load
  • at 80% full load
  • at full load
  • 31. 
    Transformer breaths in when

  • load on it increases
  • load on it decreases
  • load remains constant
  • none of the above
  • 32. 
    No-load current of a transformer has

  • has high magnitude and low power factor
  • has high magnitude and high power factor
  • has small magnitude and high power factor
  • has small magnitude and low power factor
  • 33. 
    Spacers are provided between adjacent coils

  • to provide free passage to the cooling oil
  • to insulate the coils from each other
  • both (a) and (b)
  • none of the above
  • 34. 
    Greater the secondary leakage flux

  • less will be the secondary induced e.m.f.
  • less will be the primary induced e.m.f.
  • less will be the primary terminal voltage
  • none of the above
  • 35. 
    The purpose of providing iron core in a step-up transformer is

  • to provide coupling between primary and secondary
  • to increase the magnitude of mutual flux
  • to decrease the magnitude of mag-netizing current
  • to provide all above features
  • 36. 
    The power transformer is a constant

  • voltage device
  • current device
  • power device
  • main flux device
  • 37. 
    Two transformers operating in parallel will share the load depending upon thei

  • leakage reactance
  • per unit impedance
  • efficiencies
  • ratings
  • 38. 
    If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be

  • R2/VK
  • R2IK2
  • R22!K2
  • R22/K
  • 39. 
    What will happen if the transformers working in parallel are not connected with regard to polarity ?

  • The power factor of the two trans-formers will be different from the power factor of common load
  • Incorrect polarity will result in dead short circuit
  • The transformers will not share load in proportion to their kVA ratings
  • none of the above
  • 40. 
    If the percentage impedances of the two transformers working in parallel are different, then

  • transformers will be overheated
  • power factors of both the transformers will be same
  • parallel operation will be not possible
  • 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
  • 41. 
    In a transformer the tappings are generally provided on

  • primary side
  • secondary side
  • low voltage side
  • high voltage side
  • 42. 
    The chemical used in breather for transformer should have the quality of

  • ionizing air
  • absorbing moisture
  • cleansing the transformer oil
  • cooling the transformer oil.
  • 43. 
    The chemical used in breather is

  • asbestos fiber
  • silica sand
  • sodium chloride
  • silica gel
  • 44. 
    The transformer ratings are usually expressed in terms of

  • volts
  • amperes
  • kW
  • kVA
  • 45. 
    The noise resulting from vibrations of laminations set by magnetic forces, is termed as

  • magnetostrication
  • boo
  • hum
  • zoom
  • 46. 
    Material used for construction of transformer core is usually

  • wood
  • copper
  • aluminium
  • silicon steel
  • 47. 
    The thickness of laminations used in a transformer is usually

  • 0.4 mm to 0.5 mm
  • 4 mm to 5 mm
  • 14 mm to 15 mm
  • 25 mm to 40 mm
  • 48. 
    The function of conservator in a transformer 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 sur-roundings
  • 49. 
    In a transformer the resistance between its primary and secondary is

  • zero
  • 1 ohm
  • 1000 ohms
  • infinite
  • 50. 
    A transformer oil must be free from

  • sludge
  • odour
  • gases
  • moisture
  • 51. 
    A Buchholz relay can be installed on

  • auto-transformers
  • air-cooled transformers
  • welding transformers
  • oil cooled transformers
  • 52. 
    Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds

  • 50°C
  • 80°C
  • 100°C
  • 150°C
  • 53. 
    The main reason for generation of harmonics in a transformer could be

  • fluctuating load
  • poor insulation
  • mechanical vibrations
  • saturation of core
  • 54. 
    Distribution transformers are generally designed for maximum efficiency around

  • 90% load
  • zero load
  • 25% load
  • 50% load
  • 55. 
    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
  • 56. 
    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
  • 57. 
    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
  • 58. 
    The magnetising current of a transformer is usually small because it has

  • small air gap
  • large leakage flux
  • laminated silicon steel core
  • fewer rotating parts
  • 59. 
    Which of the following does not change in an ordinary transformer ?

  • Frequency
  • Voltage
  • Current
  • Any of the above
  • 60. 
    Which of the following properties is not necessarily desirable for the material for transformer core ?

  • Low hysteresis loss
  • High permeability
  • High thermal conductivity
  • Adequate mechanical strength
  • 61. 
    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
  • 62. 
    The path of the magnetic flux in transformer should have

  • high reluctance
  • low reactance
  • high resistance
  • low resistance
  • 63. 
    Noise level test in a transformer is a

  • special test
  • routine test
  • type test
  • none of the above
  • 64. 
    Which of the following is not a routine test on transformers ?

  • Core insulation voltage test
  • Impedance test
  • Radio interference test
  • Polarity test
  • 65. 
    A transformer can have zero voltage regulation at

  • leading power factor
  • lagging power factor
  • unity power factor
  • zero power factor
  • 66. 
    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
  • 67. 
    Harmonics in transformer result in

  • increased core losses
  • increased I2R losses
  • magnetic interference with communication circuits
  • all of the above
  • 68. 
    The core used in high frequency transformer is usually

  • copper core
  • cost iron core
  • air core
  • mild steel core
  • 69. 
    The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be

  • 6400 W
  • 1600 W
  • 800 W
  • 400 W
  • 70. 
    4. 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
  • 71. 
    5. Silicon steel used in laminations mainly reduces

  • hysteresis loss
  • eddy current losses
  • copper losses
  • all of the above
  • 72. 
    Which winding of the transformer has less cross-sectional area ?

  • Primary winding
  • Secondary winding
  • Low voltage winding
  • High voltage winding
  • 73. 
    Power transformers are generally designed to have maximum efficiency around

  • no-load
  • half-load
  • near full-load
  • 10% overload
  • 74. 
    . Which of the following is the main advantage of an auto-transformer over a two winding transformer ?

  • Hysteresis losses are reduced
  • Saving in winding material
  • Copper losses are negligible
  • Eddy losses are totally eliminated
  • 75. 
    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
  • 76. 
    Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in

  • short-circuiting of the secondaries
  • 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
  • 77. 
    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
  • 78. 
    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
  • 79. 
    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
  • 80. 
    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
  • secondary voltage remains constant
  • 81. 
    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
  • 82. 
    If the supply frequency to the transformer is increased,”the iron loss will

  • not change
  • decrease
  • increase
  • any of the above
  • 83. 
    Negative voltage regulation is indicative that the load is

  • capacitive only
  • inductive only
  • inductive or resistive
  • none of the above
  • 84. 
    Iron loss of a transformer can be measured by

  • low power factor wattmeter
  • unity power factor wattmeter
  • frequency meter
  • any type of wattmeter
  • 85. 
    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
  • 86. 
    Which type of winding is used in 3phase shell-type transformer ?

  • Circular type
  • Sandwich type
  • Cylindrical type
  • Rectangular type
  • 87. 
    Open circuit test on transformers is conducted to determine

  • hysteresis losses
  • copper losses
  • core losses
  • eddy current losses
  • 88. 
    Short circuit test on transformers is conducted to determine

  • hysteresis losses
  • copper losses
  • core losses
  • eddy current losses
  • 89. 
    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.
  • 90. 
    The transformer oil should have _____ volatility and _____ viscosity.

  • low,low
  • high,high
  • low,high
  • high,low
  • 91. 
    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
  • 92. 
    The secondary winding of which of the following transformers is always kept closed ?

  • Step-up transformer
  • Step-down transformer
  • Potential transformer
  • Current transformer
  • 93. 
    The size of a transformer core will depend on

  • frequency
  • area of the core
  • flux density of the core material
  • (a) and (b) both
  • 94. 
    . N atural air coo ling is generally restricted for transformers up to

  • 1.5 MVA
  • 5 MVA
  • 15 MVA
  • 50 MVA
  • 95. 
    . A shell-type transformer has

  • high eddy current losses
  • reduced magnetic leakage
  • negligibly hysteresis losses
  • none of the above
  • 96. 
    . A transformer can have regulation closer to zero

  • on full-load
  • on overload
  • on leading power factor
  • on zero power factor
  • 97. 
    . A transformer transforms

  • voltage
  • current
  • current and voltage
  • power
  • 98. 
    . Which of the following is not the standard voltage for power supply in India ?

  • llkV
  • 33kV
  • 66 kV
  • 122 kV
  • 99. 
    . 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
  • 100. 
    . In a power or distribution transformer about 10 per cent 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
  • 101. 
    . 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
  • 102. 
    . Losses which occur in rotating electric machines and do not occur in trans formers are

  • friction and windage losses
  • magnetic losses
  • hysteresis and eddy current losses
  • copper losses
  • 103. 
    . 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
  • 104. 
    . Which of the following statements regarding an idel single-phase transformer having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ?

  • Its secondary current is 5 A
  • Its secondary voltage is 400 V
  • Its rating is 2 kVA
  • Its secondary current is 20 A
  • It is a step-up transformer
  • 105. 
    . 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
  • 106. 
    . In a transformer the resistance between its primary and secondary should be

  • zero
  • 10 Q
  • 1000 Q
  • infinity
  • 107. 
    . 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
  • 108. 
    . 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
  • 109. 
    . Which of the following protection is normally not provided on small distribution transformers ?

  • Overfluxing protection
  • Buchholz relay
  • Overcurrent protection
  • All of the above
  • 110. 
    . Which of the following acts as a protection against high voltage surges due to lightning and switching ?

  • Horn gaps
  • Thermal overload relays
  • Breather
  • Conservator
  • 111. 
    . 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
  • 112. 
    . Which of the following insulating materials can withstand the highest temperature safely ?

  • Cellulose
  • Asbestos
  • Mica
  • Glass fibre
  • 113. 
    . Which of the following parts of a transformer is visible from outside ?

  • Bushings
  • Core
  • Primary winding
  • Secondary winding
  • 114. 
    . The noise produced by a transformer is termed as

  • zoom
  • hum
  • ringing
  • buzz
  • 115. 
    . Which of the following loss in a transformer is zero even at full load ?

  • Core loss
  • Friction loss
  • Eddy current loss
  • Hysteresis loss
  • 116. 
    . Which of the following is the most likely source of harmonics in a transformer ?

  • poor insulation
  • Overload
  • loose connections
  • Core saturation
  • 117. 
    . If a transformer is continuously operated the maximum temperature rise will occur in

  • core
  • windings
  • tank
  • any of the above
  • 118. 
    . The hum in a transformer is mainly attributed to

  • load changes
  • oil in the transformer
  • magnetostriction
  • mechanical vibrations
  • 119. 
    . The maximum load that a power transformer can carry is limited by its

  • temperature rise
  • dielectric strength of oil
  • voltage ratio
  • copper loss
  • 120. 
    . The efficiency of a transformer, under heavy loads, is comparatively low because

  • copper loss becomes high in proportion to the output
  • iron loss is increased considerably
  • voltage drop both in primary and secondary becomes large
  • secondary output is much less as compared to primary input
  • 121. 
    . An open-circuit test on a transformer is conducted primarily to measure (f) none of the above

  • insulation resistance
  • copper loss
  • core loss
  • total loss
  • efficiency
  • 122. 
    . A no-load test is performed on a transformer to determine

  • core loss
  • copper loss
  • efficiency
  • magnetising current
  • magnetising current and loss
  • 123. 
    . The voltage transformation ratio of a transformer is equal to the ratio of

  • primary turns to secondary turns
  • secondary current to primary current
  • secondary induced e.m.f. to primary induced e.m.f.
  • secondary terminal voltage to primary applied voltage
  • 124. 
    . Part of the transformer which is most subject to damage from overheating is

  • iron core
  • copper winding
  • winding insulation
  • frame or case
  • transformer tank
  • 125. 
    . 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
  • 126. 
    . Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is

  • approximately equal to one
  • less than one
  • great than one
  • none of the above
  • 127. 
    . Minimum voltage regulation occurs when the power factor of the load is

  • unity
  • lagging
  • leading
  • zero
  • 128. 
    . In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of

  • less than 15 A
  • more than 15 A
  • 15 A
  • none of the above
  • 129. 
    . The efficiencies of transformers compared with that of electric motors of the same power are (6) much smaller

  • about the same
  • much higher
  • somewhat smaller
  • none of the above
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