Home / Electrical Machine / MCQ / Transformer / 160+ Transformer MCQ Questions and Answers | Electrical Engineering Objective Questions

160+ Transformer MCQ Questions and Answers | Electrical Engineering Objective Questions

November 30, 2021 , ,
160+ Transformer MCQ Questions and Answers | Electrical Engineering Objective Questions

160+ Transformer MCQ Questions and Answers | Electrical Engineering Objective Questions

Search Description: Practice 160+ Transformer MCQ Questions and Answers with explanations for Electrical Engineering, GATE, SSC JE, RRB JE, diploma exams and interviews.

Best for: Electrical Engineering students, diploma students, ITI students, GATE Electrical, SSC JE Electrical, RRB JE, technical interviews, and electrical machines objective exam preparation.

Introduction

Transformers are one of the most important topics in Electrical Machines and Power Systems. A transformer is a static device used to transfer AC electrical power from one circuit to another at the same frequency. It can step up voltage for transmission and step down voltage for safe distribution and utilization.

This post contains 160+ Transformer MCQ Questions and Answers with short explanations. The questions are arranged from easy to advanced level so that beginners can revise basic concepts first and then move toward exam-level questions. These objective questions cover transformer working principle, construction, core, windings, losses, efficiency, voltage regulation, cooling, protection, open-circuit test, short-circuit test, autotransformer, current transformer, potential transformer, and parallel operation.

Use this Transformer MCQ practice set for quick revision before semester exams, competitive exams, interviews, and online tests.

AdSense Ad Slot 1: Place responsive display ad after introduction

Table of Contents

  1. Quick Notes on Transformer
  2. Easy Level Transformer MCQs
  3. Intermediate Level Transformer MCQs
  4. Advanced Level Transformer MCQs
  5. Quick Answer Key
  6. Frequently Asked Questions
  7. SEO Labels and Related Keywords

Quick Notes on Transformer

  • A transformer works on mutual electromagnetic induction.
  • Frequency remains unchanged in a transformer.
  • The transformer core is laminated to reduce eddy current loss.
  • Open-circuit test is used to find core loss and no-load current.
  • Short-circuit test is used to find copper loss and equivalent impedance.
  • Maximum efficiency occurs when copper loss equals iron loss.
  • Transformer rating is given in kVA because power factor depends on load.
  • Buchholz relay protects oil-filled transformers from internal faults.

Easy Level Transformer MCQs

Q1. Which of the following does not change in a transformer ?
  1. Current
  2. Voltage
  3. Frequency
  4. All of the above
Answer: C. Frequency
Explanation: A transformer changes voltage and current levels, but the supply frequency remains the same.
Q2. In a transformer the energy is conveyed from primary to secondary?
  1. through cooling coil
  2. through air
  3. by the flux
  4. none of the above
Answer: C. by the flux
Explanation: Energy transfer takes place through the mutual magnetic flux linking the primary and secondary windings.
Q3. A transformer core is laminated to?
  1. reduce hysteresis loss
  2. reduce eddy current losses
  3. reduce copper losses
  4. reduce all above losses
Answer: B. reduce eddy current losses
Explanation: Laminations increase the resistance path for circulating currents and reduce eddy current loss.
Q4. The degree of mechanical vibrations produced by the laminations of a transformer depends on?
  1. tightness of clamping
  2. gauge of laminations
  3. size of laminations
  4. all of the above
Answer: D. all of the above
Explanation: Laminations increase the resistance path for circulating currents and reduce eddy current loss.
Q5. The no-load current drawn by transformer is usually what per cent of the full-load current ?
  1. 0.2 to 0.5 per cent
  2. 2 to 5 per cent
  3. 12 to 15 per cent
  4. 20 to 30 per cent
Answer: B. 2 to 5 per cent
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q6. The path of a magnetic flux in a transformer should have?
  1. high resistance
  2. high reluctance
  3. low resistance
  4. low reluctance
Answer: D. low reluctance
Explanation: low reluctance is correct because it matches the standard working principle and construction of transformers.
Q7. No-load on a transformer is carried out to determine?
  1. copper loss
  2. magnetising current
  3. magnetising current and loss
  4. efficiency of the transformer
Answer: C. magnetising current and loss
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q8. The dielectric strength of transformer oil is expected to be?
  1. lkV
  2. 33 kV
  3. 100 kV
  4. 330 kV
Answer: B. 33 kV
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q9. Sumpner's test is conducted on transformers to determine?
  1. temperature
  2. stray losses
  3. all-day efficiency
  4. none of the above
Answer: A. temperature
Explanation: Cooling keeps the winding and insulation temperature within safe limits.
Q10. The permissible flux density in case of cold rolled grain oriented steel is around?
  1. 1.7 Wb/m2
  2. 2.7 Wb/m2
  3. 3.7 Wb/m2
  4. 4.7 Wb/m2
Answer: A. 1.7 Wb/m2
Explanation: 1.7 Wb/m2 is correct because it matches the standard working principle and construction of transformers.
Q11. The efficiency of a transformer will be maximum when?
  1. copper losses = hysteresis losses
  2. hysteresis losses = eddy current losses
  3. eddy current losses = copper losses
  4. copper losses = iron losses
Answer: D. copper losses = iron losses
Explanation: Transformer efficiency is maximum when variable copper loss becomes equal to constant iron loss.
Q12. No-load current in a transformer?
  1. lags behind the voltage by about 75°
  2. leads the voltage by about 75°
  3. lags behind the voltage by about 15°
  4. leads the voltage by about 15°
Answer: A. lags behind the voltage by about 75°
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q13. The purpose of providing an iron core in a transformer is to?
  1. provide support to windings
  2. reduce hysteresis loss
  3. decrease the reluctance of the magnetic path
  4. reduce eddy current losses
Answer: C. decrease the reluctance of the magnetic path
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q14. Which of the following is not a part of transformer installation ?
  1. Conservator
  2. Breather
  3. Buchholz relay
  4. Exciter
Answer: D. Exciter
Explanation: Exciter is correct because it matches the standard working principle and construction of transformers.
Q15. While conducting short-circuit test on a transformer the following side is short circuited?
  1. High voltage side
  2. Low voltage side
  3. Primary side
  4. Secondary side
Answer: B. Low voltage side
Explanation: The short-circuit test is performed at low applied voltage and rated current, so it mainly gives full-load copper loss.
Q16. In the transformer following winding has got more cross-sectional area?
  1. Low voltage winding
  2. High voltage winding
  3. Primary winding
  4. Secondary winding
Answer: A. Low voltage winding
Explanation: Low voltage winding is correct because it matches the standard working principle and construction of transformers.
Q17. A transformer transforms?
  1. voltage
  2. current
  3. power
  4. frequency
Answer: C. power
Explanation: power is correct because it matches the standard working principle and construction of transformers.
Q18. A transformer cannot raise or lower the voltage of a D.C. supply because?
  1. there is no need to change the D.C. voltage
  2. a D.C. circuit has more losses
  3. Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
  4. none of the above
Answer: C. Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
Explanation: Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero is correct because it matches the standard working principle and construction of transformers.
Q19. Primary winding of a transformer?
  1. is always a low voltage winding
  2. is always a high voltage winding
  3. could either be a low voltage or high voltage winding
  4. none of the above
Answer: C. could either be a low voltage or high voltage winding
Explanation: could either be a low voltage or high voltage winding is correct because it matches the standard working principle and construction of transformers.
Q20. Which winding in a transformer has more number of turns ?
  1. Low voltage winding
  2. High voltage winding
  3. Primary winding
  4. Secondary winding
Answer: B. High voltage winding
Explanation: The voltage ratio of a transformer is approximately equal to its turns ratio.
Q21. Efficiency of a power transformer is of the order of?
  1. 100 per cent
  2. 98 per cent
  3. 50 per cent
  4. 25 per cent
Answer: B. 98 per cent
Explanation: 98 per cent is correct because it matches the standard working principle and construction of transformers.
Q22. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are?
  1. friction and windage losses
  2. copper losses
  3. hysteresis and eddy current losses
  4. none of the above
Answer: C. hysteresis and eddy current losses
Explanation: Iron losses are mainly hysteresis and eddy current losses, and for constant voltage and frequency they remain nearly constant.
Q23. A common method of cooling a power transformer is?
  1. natural air cooling
  2. air blast cooling
  3. oil cooling
  4. any of the above
Answer: C. oil cooling
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q24. The no load current in a transformer lags behind the applied voltage by an angle of about?
  1. 180°
  2. 120"
  3. 90°
  4. 75°
Answer: D. 75°
Explanation: 75° is correct because it matches the standard working principle and construction of transformers.
Q25. In a transformer routine efficiency depends upon?
  1. supply frequency
  2. and
  4. both
Answer: D. both
Explanation: both is correct because it matches the standard working principle and construction of transformers.
AdSense Ad Slot: Place responsive ad after Question 25
Q26. In the transformer the function of a conservator is to?
  1. provide fresh air for cooling the transformer
  2. supply cooling oil to transformer in time of need
  3. protect the transformer from damage when oil expends due to heating
  4. none of the above
Answer: C. protect the transformer from damage when oil expends due to heating
Explanation: The conservator allows transformer oil to expand and contract with temperature changes.
Q27. Natural oil cooling is used for transformers upto a rating of?
  1. 3000 kVA
  2. 1000 kVA
  3. 500 kVA
  4. 250 kVA
Answer: A. 3000 kVA
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q28. Power transformers are designed to have maximum efficiency at?
  1. nearly full load
  2. 70% full load
  3. 50% full load
  4. no load
Answer: A. nearly full load
Explanation: Transformer efficiency is maximum when variable copper loss becomes equal to constant iron loss.
Q29. The maximum efficiency of a distribution transformer is?
  1. at no load
  2. at 50% full load
  3. at 80% full load
  4. at full load
Answer: B. at 50% full load
Explanation: Transformer efficiency is maximum when variable copper loss becomes equal to constant iron loss.
Q30. Transformer breaths in when?
  1. load on it increases
  2. load on it decreases
  3. load remains constant
  4. none of the above
Answer: B. load on it decreases
Explanation: load on it decreases is correct because it matches the standard working principle and construction of transformers.
Q31. No-load current of a transformer has?
  1. has high magnitude and low power factor
  2. has high magnitude and high power factor
  3. has small magnitude and high power factor
  4. has small magnitude and low power factor
Answer: D. has small magnitude and low power factor
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q32. Spacers are provided between adjacent coils?
  1. and
  3. both
  4. none of the above
Answer: A. and
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q33. Greater the secondary leakage flux?
  1. less will be the secondary induced e.m.f
  2. less will be the primary induced e.m.f
  3. less will be the primary terminal voltage
  4. none of the above
Answer: A. less will be the secondary induced e.m.f
Explanation: less will be the secondary induced e.m.f is correct because it matches the standard working principle and construction of transformers.
Q34. The purpose of providing iron core in a step-up transformer is?
  1. to provide coupling between primary and secondary
  2. to increase the magnitude of mutual flux
  3. to decrease the magnitude of magnetizing current
  4. to provide all above features
Answer: C. to decrease the magnitude of magnetizing current
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q35. The power transformer is a constant?
  1. voltage device
  2. current device
  3. power device
  4. main flux device
Answer: D. main flux device
Explanation: main flux device is correct because it matches the standard working principle and construction of transformers.
Q36. Two transformers operating in parallel will share the load depending upon their?
  1. leakage reactance
  2. per unit impedance
  3. efficiencies
  4. ratings
Answer: B. per unit impedance
Explanation: For parallel operation, transformers must have proper polarity and suitable impedance so that load sharing is safe.
Q37. 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?
  1. R2/VK
  2. R2IK2
  3. R22!K2
  4. R22/K
Answer: B. R2IK2
Explanation: R2IK2 is correct because it matches the standard working principle and construction of transformers.
Q38. What will happen if the transformers working in parallel are not connected with regard to polarity ?
  1. The power factor of the two transformers will be different from the power factor of common load
  2. Incorrect polarity will result in dead short circuit
  3. The transformers will not share load in proportion to their kVA ratings
  4. none of the above
Answer: B. Incorrect polarity will result in dead short circuit
Explanation: For parallel operation, transformers must have proper polarity and suitable impedance so that load sharing is safe.
Q39. If the percentage impedances of the two transformers working in parallel are different, then?
  1. transformers will be overheated
  2. power factors of both the transformers will be same
  3. parallel operation will be not possible
  4. 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
Answer: D. 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
Explanation: For parallel operation, transformers must have proper polarity and suitable impedance so that load sharing is safe.
Q40. In a transformer the tappings are generally provided on?
  1. primary side
  2. secondary side
  3. low voltage side
  4. high voltage side
Answer: C. low voltage side
Explanation: low voltage side is correct because it matches the standard working principle and construction of transformers.
Q41. The use of higher flux density in the transformer design?
  1. reduces weight per kVA
  2. reduces iron losses
  3. reduces copper losses
  4. increases part load efficiency
Answer: A. reduces weight per kVA
Explanation: Transformer rating is given in kVA because losses depend on voltage and current, not directly on load power factor.
Q42. The chemical used in breather for transformer should have the quality of?
  1. ionizing air
  2. absorbing moisture
  3. cleansing the transformer oil
  4. cooling the transformer oil
Answer: B. absorbing moisture
Explanation: The breather contains silica gel, which absorbs moisture from incoming air.
Q43. The chemical used in breather is?
  1. asbestos fibre
  2. silica sand
  3. sodium chloride
  4. silica gel
Answer: D. silica gel
Explanation: The breather contains silica gel, which absorbs moisture from incoming air.
Q44. An ideal transformer has infinite values of primary and secondary inductances. The statement is?
  1. true
  2. false
Answer: B. false
Explanation: false is correct because it matches the standard working principle and construction of transformers.
Q45. The transformer ratings are usually expressed in terms of?
  1. volts
  2. amperes
  3. kW
  4. kVA
Answer: D. kVA
Explanation: Transformer rating is given in kVA because losses depend on voltage and current, not directly on load power factor.
Q46. The noise resulting from vibrations of laminations set by magnetic forces, is termed as?
  1. magnetostrication
  2. boo
  3. hum
  4. zoom
Answer: C. hum
Explanation: Laminations increase the resistance path for circulating currents and reduce eddy current loss.
Q47. Hysteresis loss in a transformer varies as CBmax = maximum flux density)?
  1. Bmax
  2. Bmax1-6
  3. Bmax1-83
  4. B max
Answer: B. Bmax1-6
Explanation: Iron losses are mainly hysteresis and eddy current losses, and for constant voltage and frequency they remain nearly constant.
Q48. Material used for construction of transformer core is usually?
  1. wood
  2. copper
  3. aluminium
  4. silicon steel
Answer: D. silicon steel
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q49. The thickness of laminations used in a transformer is usually?
  1. 0.4 mm to 0.5 mm
  2. 4 mm to 5 mm
  3. 14 mm to 15 mm
  4. 25 mm to 40 mm
Answer: A. 0.4 mm to 0.5 mm
Explanation: Laminations increase the resistance path for circulating currents and reduce eddy current loss.
Q50. The function of conservator in a transformer is?
  1. to project against'internal fault
  2. to reduce copper as well as core losses
  3. to cool the transformer oil
  4. to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings
Answer: D. to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings
Explanation: The conservator allows transformer oil to expand and contract with temperature changes.

Intermediate Level Transformer MCQs

AdSense Ad Slot 2: Place in-article ad before intermediate questions
Q51. The highest voltage for transmitting electrical power in India is?
  1. 33 kV
  2. 66 kV
  3. 132 kV
  4. 400 kV
Answer: D. 400 kV
Explanation: 400 kV is correct because it matches the standard working principle and construction of transformers.
Q52. In a transformer the resistance between its primary and secondary is?
  1. zero
  2. 1 ohm
  3. 1000 ohms
  4. infinite
Answer: D. infinite
Explanation: infinite is correct because it matches the standard working principle and construction of transformers.
Q53. A transformer oil must be free from?
  1. sludge
  2. odour
  3. gases
  4. moisture
Answer: D. moisture
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q54. A Buchholz relay can be installed on?
  1. auto-transformers
  2. air-cooled transformers
  3. welding transformers
  4. oil cooled transformers
Answer: D. oil cooled transformers
Explanation: Buchholz relay protects oil-filled transformers against internal faults by detecting gas formation.
Q55. Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds?
  1. 50°C
  2. 80°C
  3. 100°C
  4. 150°C
Answer: D. 150°C
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q56. The main reason for generation of harmonics in a transformer could be?
  1. fluctuating load
  2. poor insulation
  3. mechanical vibrations
  4. saturation of core
Answer: D. saturation of core
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q57. Distribution transformers are generally designed for maximum efficiency around?
  1. 90% load
  2. zero load
  3. 25% load
  4. 50% load
Answer: D. 50% load
Explanation: Transformer efficiency is maximum when variable copper loss becomes equal to constant iron loss.
Q58. Which of the following property is not necessarily desirable in the material for transformer core ?
  1. Mechanical strength
  2. Low hysteresis loss
  3. High thermal conductivity
  4. High permeability
Answer: C. High thermal conductivity
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q59. Star/star transformers work satisfactorily when?
  1. load is unbalanced only
  2. load is balanced only
  3. on balanced as well as unbalanced loads
  4. none of the above
Answer: B. load is balanced only
Explanation: load is balanced only is correct because it matches the standard working principle and construction of transformers.
Q60. Delta/star transformer works satisfactorily when?
  1. load is balanced only
  2. load is unbalanced only
  3. on balanced as well as unbalanced loads
  4. none of the above
Answer: C. on balanced as well as unbalanced loads
Explanation: on balanced as well as unbalanced loads is correct because it matches the standard working principle and construction of transformers.
Q61. Buchholz's relay gives warning and protection against?
  1. electrical fault inside the transformer itself
  2. electrical fault outside the transformer in outgoing feeder
  3. for both outside and inside faults
  4. none of the above
Answer: A. electrical fault inside the transformer itself
Explanation: Buchholz relay protects oil-filled transformers against internal faults by detecting gas formation.
Q62. The magnetising current of a transformer is usually small because it has?
  1. small air gap
  2. large leakage flux
  3. laminated silicon steel core
  4. fewer rotating parts
Answer: A. small air gap
Explanation: small air gap is correct because it matches the standard working principle and construction of transformers.
Q63. Which of the following does not change in an ordinary transformer ?
  1. Frequency
  2. Voltage
  3. Current
  4. Any of the above
Answer: A. Frequency
Explanation: A transformer changes voltage and current levels, but the supply frequency remains the same.
Q64. Which of the following properties is not necessarily desirable for the material for transformer core ?
  1. Low hysteresis loss
  2. High permeability
  3. High thermal conductivity
  4. Adequate mechanical strength
Answer: C. High thermal conductivity
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q65. The leakage flux in a transformer depends upon?
  1. load current
  2. load current and voltage
  3. load current, voltage and frequency
  4. load current, voltage, frequency and power factor
Answer: A. load current
Explanation: load current is correct because it matches the standard working principle and construction of transformers.
Q66. The path of the magnetic flux in transformer should have?
  1. high reluctance
  2. low reactance
  3. high resistance
  4. low resistance
Answer: B. low reactance
Explanation: low reactance is correct because it matches the standard working principle and construction of transformers.
Q67. Noise level test in a transformer is a?
  1. special test
  2. routine test
  3. type test
  4. none of the above
Answer: C. type test
Explanation: Transformer hum is mainly produced by magnetostriction and vibration of the core laminations.
Q68. Which of the following is not a routine test on transformers ?
  1. Core insulation voltage test
  2. Impedance test
  3. Radio interference test
  4. Polarity test
Answer: C. Radio interference test
Explanation: Radio interference test is correct because it matches the standard working principle and construction of transformers.
Q69. A transformer can have zero voltage regulation at?
  1. leading power factor
  2. lagging power factor
  3. unity power factor
  4. zero power factor
Answer: A. leading power factor
Explanation: Voltage regulation shows how much secondary voltage changes from no-load to full-load.
Q70. Helical coils can be used on?
  1. low voltage side of high kVA trans¬formers
  2. high frequency transformers
  3. high voltage side of small capacity transformers
  4. high voltage side of high kVA rating transformers
Answer: A. low voltage side of high kVA trans¬formers
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q71. Harmonics in transformer result in?
  1. increased core losses
  2. increased I2R losses
  3. magnetic interference with communication circuits
  4. all of the above
Answer: D. all of the above
Explanation: Harmonics are mainly caused by nonlinear magnetisation and core saturation.
Q72. The core used in high frequency transformer is usually?
  1. copper core
  2. cost iron core
  3. air core
  4. mild steel core
Answer: C. air core
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q73. The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be?
  1. 6400 W
  2. 1600 W
  3. 800 W
  4. 400 W
Answer: D. 400 W
Explanation: Copper loss varies with the square of load current and becomes important at heavy load.
Q74. ?
Answer: .
Explanation: is correct because it matches the standard working principle and construction of transformers.
Q75. The value of flux involved in the e.m.f. equation of a transformer is?
  1. average value
  2. r.m.s. value
  3. maximum value
  4. instantaneous value
Answer: C. maximum value
Explanation: maximum value is correct because it matches the standard working principle and construction of transformers.
AdSense Ad Slot: Place responsive ad after Question 75
Q76. Silicon steel used in laminations mainly reduces?
  1. hysteresis loss
  2. eddy current losses
  3. copper losses
  4. all of the above
Answer: A. hysteresis loss
Explanation: Laminations increase the resistance path for circulating currents and reduce eddy current loss.
Q77. Which winding of the transformer has less cross-sectional area ?
  1. Primary winding
  2. Secondary winding
  3. Low voltage winding
  4. High voltage winding
Answer: D. High voltage winding
Explanation: High voltage winding is correct because it matches the standard working principle and construction of transformers.
Q78. Power transformers are generally designed to have maximum efficiency around?
  1. no-load
  2. half-load
  3. near full-load
  4. 10% overload
Answer: C. near full-load
Explanation: Transformer efficiency is maximum when variable copper loss becomes equal to constant iron loss.
Q79. Which of the following is the main advantage of an auto-transformer over a two winding transformer ?
  1. Hysteresis losses are reduced
  2. Saving in winding material
  3. Copper losses are negligible
  4. Eddy losses are totally eliminated
Answer: B. Saving in winding material
Explanation: An autotransformer saves copper because part of the winding is common to both primary and secondary.
Q80. During short circuit test iron losses are negligible because?
  1. the current on secondary side is negligible
  2. the voltage on secondary side does not vary
  3. the voltage applied on primary side is low
  4. full-load current is not supplied to the transformer
Answer: C. the voltage applied on primary side is low
Explanation: The short-circuit test is performed at low applied voltage and rated current, so it mainly gives full-load copper loss.
Q81. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in?
  1. short-circuiting of the secondaries
  2. power factor of one of the trans¬formers is leading while that of the other lagging
  3. transformers having higher copper losses will have negligible core losses
  4. loading of the transformers not in proportion to their kVA ratings
Answer: D. loading of the transformers not in proportion to their kVA ratings
Explanation: For parallel operation, transformers must have proper polarity and suitable impedance so that load sharing is safe.
Q82. 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?
  1. Conservator
  2. Breather
  3. Bushings
  4. Buchholz relay
Answer: A. Conservator
Explanation: The conservator allows transformer oil to expand and contract with temperature changes.
Q83. An ideal transformer is one which has?
  1. no losses and magnetic leakage
  2. interleaved primary and secondary windings
  3. a common core for its primary and secondary windings
  4. core of stainless steel and winding of pure copper metal
  5. none of the above
Answer: A. no losses and magnetic leakage
Explanation: no losses and magnetic leakage is correct because it matches the standard working principle and construction of transformers.
Q84. When a given transformer is run at its rated voltage but reduced frequency, its?
  1. flux density remains unaffected
  2. iron losses are reduced
  3. core flux density is reduced
  4. core flux density is increased
Answer: D. core flux density is increased
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q85. In an actual transformer the iron loss remains practically constant from no-load to full-load because?
  1. value of transformation ratio remains constant
  2. permeability of transformer core remains constant
  3. secondary voltage remains constant
  4. primary voltage remains constant
Answer: C. secondary voltage remains constant
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q86. An ideal transformer will have maximum efficiency at a load such that?
  1. copper loss = iron loss
  2. copper loss iron loss
  3. none of the above
Answer: A. copper loss = iron loss
Explanation: Transformer efficiency is maximum when variable copper loss becomes equal to constant iron loss.
Q87. If the supply frequency to the transformer is increased,"the iron loss will?
  1. not change
  2. decrease
  3. increase
  4. any of the above
Answer: C. increase
Explanation: Iron losses are mainly hysteresis and eddy current losses, and for constant voltage and frequency they remain nearly constant.
Q88. Negative voltage regulation is indicative that the load is?
  1. capacitive only
  2. inductive only
  3. inductive or resistive
  4. none of the above
Answer: A. capacitive only
Explanation: Voltage regulation shows how much secondary voltage changes from no-load to full-load.
Q89. Iron loss of a transformer can be measured by?
  1. low power factor wattmeter
  2. unity power factor wattmeter
  3. frequency meter
  4. any type of wattmeter
Answer: A. low power factor wattmeter
Explanation: Iron losses are mainly hysteresis and eddy current losses, and for constant voltage and frequency they remain nearly constant.
Q90. When secondary of a current transformer is open-circuited its iron core will be?
  1. hot because of heavy iron losses taking place in it due to high flux density
  2. hot because primary will carry heavy current
  3. cool as there is no secondary current
  4. none of above will happen
Answer: A. hot because of heavy iron losses taking place in it due to high flux density
Explanation: The secondary of a CT should not be open-circuited because dangerous high voltage and core saturation may occur.
Q91. The transformer laminations are insulated from each other by?
  1. mica strip
  2. thin coat of varnish
  3. paper
  4. any of the above
Answer: B. thin coat of varnish
Explanation: Laminations increase the resistance path for circulating currents and reduce eddy current loss.
Q92. Which type of winding is used in 3phase shell-type transformer ?
  1. Circular type
  2. Sandwich type
  3. Cylindrical type
  4. Rectangular type
Answer: B. Sandwich type
Explanation: Sandwich type is correct because it matches the standard working principle and construction of transformers.
Q93. During open circuit test of a transformer?
  1. primary is supplied rated voltage
  2. primary is supplied full-load current
  3. primary is supplied current at reduced voltage
  4. primary is supplied rated kVA
Answer: A. primary is supplied rated voltage
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q94. Open circuit test on transformers is conducted to determine?
  1. hysteresis losses
  2. copper losses
  3. core losses
  4. eddy current losses
Answer: C. core losses
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q95. Short circuit test on transformers is conducted to determine?
  1. hysteresis losses
  2. copper losses
  3. core losses
  4. eddy current losses
Answer: B. copper losses
Explanation: The short-circuit test is performed at low applied voltage and rated current, so it mainly gives full-load copper loss.
Q96. For the parallel operation of single phase transformers it is necessary that they should have?
  1. same efficiency
  2. same polarity
  3. same kVA rating
  4. same number of turns on the secondary side
Answer: B. same polarity
Explanation: For parallel operation, transformers must have proper polarity and suitable impedance so that load sharing is safe.
Q97. The transformer oil should have _____ volatility and _____ viscosity.
  1. low,low
  2. high,high
  3. low,high
  4. high,low
Answer: A. low,low
Explanation: Transformer oil provides insulation and cooling, so it should have high dielectric strength and low moisture content.
Q98. The function of breather in a transformer is?
  1. to provide oxygen inside the tank
  2. to cool the coils during reduced load
  3. to cool the transformer oil
  4. to arrest flow of moisture when outside air enters the transformer
Answer: D. to arrest flow of moisture when outside air enters the transformer
Explanation: The breather contains silica gel, which absorbs moisture from incoming air.
Q99. The secondary winding of which of the following transformers is always kept closed ?
  1. Step-up transformer
  2. Step-down transformer
  3. Potential transformer
  4. Current transformer
Answer: D. Current transformer
Explanation: The secondary of a CT should not be open-circuited because dangerous high voltage and core saturation may occur.
Q100. The size of a transformer core will depend on?
  1. and
  2. both
  3. flux density of the core material
Answer: D.
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q101. Natural air coo ling is generally restricted for transformers up to?
  1. 1.5 MVA
  2. 5 MVA
  3. 15 MVA
  4. 50 MVA
Answer: A. 1.5 MVA
Explanation: 1.5 MVA is correct because it matches the standard working principle and construction of transformers.
Q102. A shell-type transformer has?
  1. high eddy current losses
  2. reduced magnetic leakage
  3. negligibly hysteresis losses
  4. none of the above
Answer: B. reduced magnetic leakage
Explanation: reduced magnetic leakage is correct because it matches the standard working principle and construction of transformers.
Q103. A transformer can have regulation closer to zero?
  1. on full-load
  2. on overload
  3. on leading power factor
  4. on zero power factor
Answer: C. on leading power factor
Explanation: Voltage regulation shows how much secondary voltage changes from no-load to full-load.
Q104. A transformer transforms?
  1. voltage
  2. current
  3. current and voltage
  4. power
Answer: D. power
Explanation: power is correct because it matches the standard working principle and construction of transformers.
Q105. Which of the following is not the standard voltage for power supply in India ?
  1. 11 kV
  2. 33kV
  3. 66 kV
  4. 122 kV
Answer: D. 122 kV
Explanation: 122 kV is correct because it matches the standard working principle and construction of transformers.
Q106. Reduction in core losses and increase in permeability are obtained with transformer employing?
  1. core built-up of laminations of cold rolled grain oriented steel
  2. core built-up of laminations of hot rolled sheet
  3. either of the above
  4. none of the above
Answer: A. core built-up of laminations of cold rolled grain oriented steel
Explanation: Laminations increase the resistance path for circulating currents and reduce eddy current loss.
Q107. In a power or distribution transformer about 10 per cent end turns are heavily insulated?
  1. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
  2. to absorb the line surge voltage and save the winding of transformer from damage
  3. to reflect the line surge and save the winding of a transformer from damage
  4. none of the above
Answer: A. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
Explanation: The voltage ratio of a transformer is approximately equal to its turns ratio.
Q108. For given applied voltage, with the increase in frequency of the applied voltage?
  1. eddy current loss will decrease
  2. eddy current loss will increase
  3. eddy current loss will remain unchanged
  4. none of the above
Answer: C. eddy current loss will remain unchanged
Explanation: Iron losses are mainly hysteresis and eddy current losses, and for constant voltage and frequency they remain nearly constant.
Q109. Losses which occur in rotating electric machines and do not occur in trans formers are?
  1. friction and windage losses
  2. magnetic losses
  3. hysteresis and eddy current losses
  4. copper losses
Answer: A. friction and windage losses
Explanation: friction and windage losses is correct because it matches the standard working principle and construction of transformers.
Q110. In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are?
  1. hysteresis and eddy current losses
  2. friction and windage losses
  3. copper losses
  4. none of the above
Answer: A. hysteresis and eddy current losses
Explanation: Iron losses are mainly hysteresis and eddy current losses, and for constant voltage and frequency they remain nearly constant.

Advanced Level Transformer MCQs

AdSense Ad Slot 3: Place in-article ad before advanced questions
Q111. Which of the following statements regarding an ideal 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 ?
  1. Its secondary current is 5 A
  2. Its secondary voltage is 400 V
  3. Its rating is 2 kVA
  4. Its secondary current is 20 A
  5. It is a step-up transformer
Answer: D. Its secondary current is 20 A
Explanation: Its secondary current is 20 A is correct because it matches the standard working principle and construction of transformers.
Q112. In a transformer the resistance between its primary and secondary should be?
  1. zero
  2. 10 Q
  3. 1000 Q
  4. infinity
Answer: D. infinity
Explanation: infinity is correct because it matches the standard working principle and construction of transformers.
Q113. A good voltage regulation of a transformer means?
  1. output voltage fluctuation from no load to full load is least
  2. output voltage fluctuation with power factor is least
  3. difference between primary and secondary voltage is least
  4. difference between primary and secondary voltage is maximum
Answer: A. output voltage fluctuation from no load to full load is least
Explanation: Voltage regulation shows how much secondary voltage changes from no-load to full-load.
Q114. For a transformer, operating at constant load current, maximum efficiency will occur at?
  1. 0.8 leading power factor
  2. 0.8 lagging power factor
  3. zero power factor
  4. unity power factor
Answer: D. unity power factor
Explanation: Transformer efficiency is maximum when variable copper loss becomes equal to constant iron loss.
Q115. Which of the following protection is normally not provided on small distribution transformers ?
  1. Overfluxing protection
  2. Buchholz relay
  3. Overcurrent protection
  4. All of the above
Answer: B. Buchholz relay
Explanation: Buchholz relay protects oil-filled transformers against internal faults by detecting gas formation.
Q116. Which of the following acts as a protection against high voltage surges due to lightning and switching ?
  1. Horn gaps
  2. Thermal overload relays
  3. Breather
  4. Conservator
Answer: A. Horn gaps
Explanation: Horn gaps is correct because it matches the standard working principle and construction of transformers.
Q117. The efficiency of two identical transformers under load conditions can be determined by?
  1. short-circuit test
  2. back-to-back test
  3. open circuit test
  4. any of the above
Answer: B. back-to-back test
Explanation: back-to-back test is correct because it matches the standard working principle and construction of transformers.
Q118. Which of the following insulating materials can withstand the highest temperature safely ?
  1. Cellulose
  2. Asbestos
  3. Mica
  4. Glass fibre
Answer: C. Mica
Explanation: Cooling keeps the winding and insulation temperature within safe limits.
Q119. Which of the following parts of a transformer is visible from outside ?
  1. Bushings
  2. Core
  3. Primary winding
  4. Secondary winding
Answer: A. Bushings
Explanation: Bushings is correct because it matches the standard working principle and construction of transformers.
Q120. The noise produced by a transformer is termed as?
  1. zoom
  2. hum
  3. ringing
  4. buzz
Answer: B. hum
Explanation: Transformer hum is mainly produced by magnetostriction and vibration of the core laminations.
Q121. Which of the following loss in a transformer is zero even at full load ?
  1. Core loss
  2. Friction loss
  3. Eddy current loss
  4. Hysteresis loss
Answer: B. Friction loss
Explanation: Friction loss is correct because it matches the standard working principle and construction of transformers.
Q122. Which of the following is the most likely source of harmonics in a transformer ?
  1. poor insulation
  2. Overload
  3. loose connections
  4. Core saturation
Answer: D. Core saturation
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q123. If a transformer is continuously operated the maximum temperature rise will occur in?
  1. core
  2. windings
  3. tank
  4. any of the above
Answer: B. windings
Explanation: Cooling keeps the winding and insulation temperature within safe limits.
Q124. The hum in a transformer is mainly attributed to?
  1. load changes
  2. oil in the transformer
  3. magnetostriction
  4. mechanical vibrations
Answer: C. magnetostriction
Explanation: Transformer hum is mainly produced by magnetostriction and vibration of the core laminations.
Q125. The maximum load that a power transformer can carry is limited by its?
  1. temperature rise
  2. dielectric strength of oil
  3. voltage ratio
  4. copper loss
Answer: C. voltage ratio
Explanation: voltage ratio is correct because it matches the standard working principle and construction of transformers.
AdSense Ad Slot: Place responsive ad after Question 125
Q126. The efficiency of a transformer, under heavy loads, is comparatively low because?
  1. copper loss becomes high in proportion to the output
  2. iron loss is increased considerably
  3. voltage drop both in primary and secondary becomes large
  4. secondary output is much less as compared to primary input
Answer: A. copper loss becomes high in proportion to the output
Explanation: Copper loss varies with the square of load current and becomes important at heavy load.
Q127. An open-circuit test on a transformer is conducted primarily to measure?
  1. insulation resistance
  2. copper loss
  3. core loss
  4. total loss
  5. efficiency (f) none of the above
Answer: C. core loss
Explanation: The transformer core provides a low-reluctance path for the alternating magnetic flux.
Q128. A no-load test is performed on a transformer to determine?
  1. core loss
  2. copper loss
  3. efficiency
  4. magnetising current
  5. magnetising current and loss
Answer: E. magnetising current and loss
Explanation: The no-load or open-circuit test mainly gives core loss and magnetising current because secondary current is almost zero.
Q129. The voltage transformation ratio of a transformer is equal to the ratio of?
  1. primary turns to secondary turns
  2. secondary current to primary current
  3. secondary induced e.m.f. to primary induced e.m.f
  4. secondary terminal voltage to primary applied voltage
Answer: C. secondary induced e.m.f. to primary induced e.m.f
Explanation: secondary induced e.m.f. to primary induced e.m.f is correct because it matches the standard working principle and construction of transformers.
Q130. Part of the transformer which is most subject to damage from overheating is?
  1. iron core
  2. copper winding
  3. winding insulation
  4. frame or case
  5. transformer tank
Answer: C. winding insulation
Explanation: winding insulation is correct because it matches the standard working principle and construction of transformers.
Q131. If a transformer is switched on to a voltage more than the rated voltage?
  1. its power factor will deteriorate
  2. its power factor will increase
  3. its power factor will remain unaffected
  4. its power factor will be zero
Answer: A. its power factor will deteriorate
Explanation: its power factor will deteriorate is correct because it matches the standard working principle and construction of transformers.
Q132. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is?
  1. approximately equal to one
  2. less than one
  3. greater than one
  4. none of the above
Answer: A. approximately equal to one
Explanation: Copper loss varies with the square of load current and becomes important at heavy load.
Q133. Minimum voltage regulation occurs when the power factor of the load is?
  1. unity
  2. lagging
  3. leading
  4. zero
Answer: C. leading
Explanation: Voltage regulation shows how much secondary voltage changes from no-load to full-load.
Q134. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of?
  1. less than 15 A
  2. more than 15 A
  3. 15 A
  4. none of the above
Answer: A. less than 15 A
Explanation: The voltage ratio of a transformer is approximately equal to its turns ratio.
Q135. The efficiencies of transformers compared with that of electric motors of the same power are?
  1. about the same
  2. much smaller
  3. much higher
  4. somewhat smaller
  5. none of the above
Answer: C. much higher
Explanation: much higher is correct because it matches the standard working principle and construction of transformers.
Q136. What is the basic working principle of a transformer?
  1. Electrostatic induction
  2. Mutual electromagnetic induction
  3. Chemical reaction
  4. Thermionic emission
Answer: B. Mutual electromagnetic induction
Explanation: A transformer works because changing current in the primary creates changing flux that induces voltage in the secondary.
Q137. Which transformer is used to increase voltage level?
  1. Step-down transformer
  2. Isolation transformer
  3. Step-up transformer
  4. Current transformer
Answer: C. Step-up transformer
Explanation: A step-up transformer has more secondary turns than primary turns, so secondary voltage increases.
Q138. Which transformer is used to decrease voltage level?
  1. Step-up transformer
  2. Step-down transformer
  3. Auto-transformer only
  4. Potential transformer only
Answer: B. Step-down transformer
Explanation: A step-down transformer has fewer secondary turns than primary turns, so secondary voltage decreases.
Q139. In an ideal transformer, input power is equal to:
  1. Output power
  2. Copper loss
  3. Iron loss
  4. Zero
Answer: A. Output power
Explanation: An ideal transformer has no losses, so input power and output power are equal.
Q140. The transformer core is generally made of:
  1. Copper sheets
  2. Silicon steel laminations
  3. Aluminium bars
  4. Wood
Answer: B. Silicon steel laminations
Explanation: Silicon steel laminations give high permeability and reduced core losses.
Q141. Which loss is reduced by using thin laminated core sheets?
  1. Friction loss
  2. Windage loss
  3. Eddy current loss
  4. Bearing loss
Answer: C. Eddy current loss
Explanation: Thin laminations reduce circulating eddy currents inside the core.
Q142. Which transformer test is mainly used to find core loss?
  1. Open-circuit test
  2. Short-circuit test
  3. Polarity test
  4. Impulse test
Answer: A. Open-circuit test
Explanation: In open-circuit test, current is very small, so wattmeter reading mainly represents core loss.
Q143. Which transformer test is mainly used to find full-load copper loss?
  1. Open-circuit test
  2. Short-circuit test
  3. No-load test only
  4. Insulation resistance test
Answer: B. Short-circuit test
Explanation: In short-circuit test, rated current flows at low voltage, so wattmeter reading gives copper loss.
Q144. Why are transformer ratings expressed in kVA?
  1. Because power factor is fixed
  2. Because losses depend on voltage and current
  3. Because transformers produce active power
  4. Because frequency changes
Answer: B. Because losses depend on voltage and current
Explanation: Transformer heating depends mainly on voltage and current, while load power factor may vary.
Q145. Which part connects transformer windings to external circuits?
  1. Bushings
  2. Breather
  3. Conservator
  4. Radiator
Answer: A. Bushings
Explanation: Bushings provide insulated terminals for bringing leads out of the transformer tank.
Q146. Which device protects an oil-filled transformer from internal faults?
  1. Buchholz relay
  2. Silica gel
  3. Radiator fan
  4. Tap changer knob
Answer: A. Buchholz relay
Explanation: Buchholz relay detects gas caused by internal faults in oil-filled transformers.
Q147. Silica gel in transformer breather changes colour when it:
  1. Absorbs moisture
  2. Absorbs oxygen
  3. Cools oil
  4. Increases voltage
Answer: A. Absorbs moisture
Explanation: Silica gel absorbs moisture from air entering the conservator system.
Q148. In a transformer, leakage flux causes:
  1. Voltage drop
  2. Zero impedance
  3. Frequency change
  4. Mechanical output
Answer: A. Voltage drop
Explanation: Leakage flux produces leakage reactance and contributes to voltage drop under load.
Q149. The turns ratio of a transformer is 1:4. It is generally a:
  1. Step-down transformer
  2. Step-up transformer
  3. Current transformer only
  4. Isolation transformer
Answer: B. Step-up transformer
Explanation: If secondary turns are four times primary turns, secondary voltage is increased.
Q150. A 1:1 transformer is mainly used for:
  1. Isolation
  2. Frequency conversion
  3. Changing DC to AC
  4. Increasing current only
Answer: A. Isolation
Explanation: A 1:1 transformer gives electrical isolation without changing voltage level significantly.
Q151. Which loss is almost absent in a transformer compared with a motor?
  1. Friction and windage loss
  2. Copper loss
  3. Core loss
  4. Eddy current loss
Answer: A. Friction and windage loss
Explanation: A transformer has no rotating part, so friction and windage losses are absent.
Q152. If load current increases, transformer copper loss:
  1. Decreases
  2. Increases
  3. Becomes zero
  4. Does not change
Answer: B. Increases
Explanation: Copper loss is proportional to the square of current, so it increases with load current.
Q153. If supply frequency is reduced at rated voltage, core flux density:
  1. Increases
  2. Decreases
  3. Becomes zero
  4. Remains exactly same
Answer: A. Increases
Explanation: Flux is inversely proportional to frequency for a fixed voltage, so reducing frequency increases flux density.
Q154. Which transformer has common winding for primary and secondary?
  1. Auto-transformer
  2. Two-winding transformer
  3. Current transformer
  4. Shell transformer only
Answer: A. Auto-transformer
Explanation: An autotransformer uses a common part of winding for both input and output.
Q155. Which transformer is used with measuring instruments to step down high voltage?
  1. Potential transformer
  2. Current transformer
  3. Welding transformer
  4. Distribution transformer
Answer: A. Potential transformer
Explanation: Potential transformers reduce high voltage to safe measurable values.
Q156. Which transformer is used to measure high current safely?
  1. Potential transformer
  2. Current transformer
  3. Isolation transformer
  4. Pulse transformer
Answer: B. Current transformer
Explanation: Current transformers reduce large current to a small standard current for metering and protection.
Q157. The secondary of a current transformer should never be:
  1. Short-circuited
  2. Open-circuited
  3. Connected to ammeter
  4. Loaded with burden
Answer: B. Open-circuited
Explanation: Open secondary of a CT can produce dangerous high voltage and overheating.
Q158. Oil in transformer performs which two main functions?
  1. Cooling and insulation
  2. Speed control and braking
  3. Frequency control and filtering
  4. Mechanical support only
Answer: A. Cooling and insulation
Explanation: Transformer oil removes heat and provides electrical insulation.
Q159. Which load power factor may give negative voltage regulation?
  1. Leading power factor
  2. Lagging power factor
  3. Unity power factor only
  4. Zero lagging only
Answer: A. Leading power factor
Explanation: A leading power factor load may cause a voltage rise, resulting in negative regulation.
Q160. Which factor mainly limits the continuous loading of a transformer?
  1. Temperature rise
  2. Shaft speed
  3. Mechanical torque
  4. Rotor balance
Answer: A. Temperature rise
Explanation: Transformer loading is limited by heating of windings and insulation.

Quick Answer Key

Use this short answer key for fast revision after solving the MCQs.

Question No.Answer
1C. Frequency
2C. by the flux
3B. reduce eddy current losses
4D. all of the above
5B. 2 to 5 per cent
6D. low reluctance
7C. magnetising current and loss
8B. 33 kV
9A. temperature
10A. 1.7 Wb/m2
11D. copper losses = iron losses
12A. lags behind the voltage by about 75°
13C. decrease the reluctance of the magnetic path
14D. Exciter
15B. Low voltage side
16A. Low voltage winding
17C. power
18C. Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
19C. could either be a low voltage or high voltage winding
20B. High voltage winding
21B. 98 per cent
22C. hysteresis and eddy current losses
23C. oil cooling
24D. 75°
25D. both
26C. protect the transformer from damage when oil expends due to heating
27A. 3000 kVA
28A. nearly full load
29B. at 50% full load
30B. load on it decreases
31D. has small magnitude and low power factor
32A. and
33A. less will be the secondary induced e.m.f
34C. to decrease the magnitude of magnetizing current
35D. main flux device
36B. per unit impedance
37B. R2IK2
38B. Incorrect polarity will result in dead short circuit
39D. 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
40C. low voltage side
41A. reduces weight per kVA
42B. absorbing moisture
43D. silica gel
44B. false
45D. kVA
46C. hum
47B. Bmax1-6
48D. silicon steel
49A. 0.4 mm to 0.5 mm
50D. to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings
51D. 400 kV
52D. infinite
53D. moisture
54D. oil cooled transformers
55D. 150°C
56D. saturation of core
57D. 50% load
58C. High thermal conductivity
59B. load is balanced only
60C. on balanced as well as unbalanced loads
61A. electrical fault inside the transformer itself
62A. small air gap
63A. Frequency
64C. High thermal conductivity
65A. load current
66B. low reactance
67C. type test
68C. Radio interference test
69A. leading power factor
70A. low voltage side of high kVA trans¬formers
71D. all of the above
72C. air core
73D. 400 W
74.
75C. maximum value
76A. hysteresis loss
77D. High voltage winding
78C. near full-load
79B. Saving in winding material
80C. the voltage applied on primary side is low
81D. loading of the transformers not in proportion to their kVA ratings
82A. Conservator
83A. no losses and magnetic leakage
84D. core flux density is increased
85C. secondary voltage remains constant
86A. copper loss = iron loss
87C. increase
88A. capacitive only
89A. low power factor wattmeter
90A. hot because of heavy iron losses taking place in it due to high flux density
91B. thin coat of varnish
92B. Sandwich type
93A. primary is supplied rated voltage
94C. core losses
95B. copper losses
96B. same polarity
97A. low,low
98D. to arrest flow of moisture when outside air enters the transformer
99D. Current transformer
100D.
101A. 1.5 MVA
102B. reduced magnetic leakage
103C. on leading power factor
104D. power
105D. 122 kV
106A. core built-up of laminations of cold rolled grain oriented steel
107A. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
108C. eddy current loss will remain unchanged
109A. friction and windage losses
110A. hysteresis and eddy current losses
111D. Its secondary current is 20 A
112D. infinity
113A. output voltage fluctuation from no load to full load is least
114D. unity power factor
115B. Buchholz relay
116A. Horn gaps
117B. back-to-back test
118C. Mica
119A. Bushings
120B. hum
121B. Friction loss
122D. Core saturation
123B. windings
124C. magnetostriction
125C. voltage ratio
126A. copper loss becomes high in proportion to the output
127C. core loss
128E. magnetising current and loss
129C. secondary induced e.m.f. to primary induced e.m.f
130C. winding insulation
131A. its power factor will deteriorate
132A. approximately equal to one
133C. leading
134A. less than 15 A
135C. much higher
136B. Mutual electromagnetic induction
137C. Step-up transformer
138B. Step-down transformer
139A. Output power
140B. Silicon steel laminations
141C. Eddy current loss
142A. Open-circuit test
143B. Short-circuit test
144B. Because losses depend on voltage and current
145A. Bushings
146A. Buchholz relay
147A. Absorbs moisture
148A. Voltage drop
149B. Step-up transformer
150A. Isolation
151A. Friction and windage loss
152B. Increases
153A. Increases
154A. Auto-transformer
155A. Potential transformer
156B. Current transformer
157B. Open-circuited
158A. Cooling and insulation
159A. Leading power factor
160A. Temperature rise

Important Transformer Interview Questions

  • Why does a transformer work only on AC supply?
  • Why is transformer core laminated?
  • Why is transformer rating given in kVA?
  • What is the difference between power transformer and distribution transformer?
  • What is the function of Buchholz relay?
  • Why is the secondary of a current transformer never kept open?
  • What is voltage regulation of a transformer?
  • What are open-circuit and short-circuit tests?

Frequently Asked Questions on Transformer MCQ

What is a transformer?

A transformer is a static electrical machine that transfers AC power from one circuit to another by mutual electromagnetic induction.

Which quantity does not change in a transformer?

Frequency does not change in an ordinary transformer. Voltage and current may change according to the turns ratio.

Why is the transformer core laminated?

The transformer core is laminated to reduce eddy current loss and improve efficiency.

Which test gives transformer core loss?

The open-circuit test gives core or iron loss because no-load current is very small.

Which test gives transformer copper loss?

The short-circuit test gives full-load copper loss because rated current flows at low applied voltage.

Why are transformers rated in kVA?

Transformers are rated in kVA because their losses depend mainly on voltage and current, while load power factor is not fixed.

Conclusion

These Transformer MCQ Questions and Answers are useful for building strong fundamentals in electrical machines. First revise the basic working principle, construction, losses, tests, and protection parts. After that, solve the intermediate and advanced questions for better exam preparation.

For better results, try to solve the questions without seeing the answer first. Then read the short explanation to understand the concept clearly.

AdSense Ad Slot 4: Place responsive ad after conclusion

SEO Labels and Related Keywords

Suggested Blogger Labels: Transformer, Electrical Machines, Electrical Engineering MCQ, GATE Electrical, SSC JE Electrical, RRB JE, Interview Questions, Objective Questions

Related Keywords: Transformer MCQ Questions, Transformer Objective Questions and Answers, Electrical Machines MCQ, Transformer Interview Questions, GATE Electrical MCQ, SSC JE Electrical Questions, RRB JE Electrical MCQ, Power Transformer MCQ, Distribution Transformer MCQ, Transformer Online Test.

Internal Linking Suggestions

  • DC Generator MCQ Questions and Answers
  • DC Motor MCQ Questions and Answers
  • Electrical Machines MCQ Question Series
  • Power System MCQ Questions and Answers
Explore more on ElectricalTech Power System Electrical Machines Electronics Projects MCQs

No comments

Subscribe to: Post Comments ( Atom )