Hi Learners, in this article we have listed 60+ important MCQs on Transformer which will be useful for your competitive exams, various interviews, viva, and other exams. The questions and answers are all collected from different exams and interviews of previous years.
These listed MCQs will be helpful for your conceptual clarity and preparation about Transformer.
1. What is Transformer?
a) Transformer is a device used to convert low alternating voltage to a high alternating voltage
b) Transformer is a device used to convert alternating current to direct current
c) Transformer is a device used to convert low alternating current to a high alternating current
d) Transformers are used only for low alternating
Answer: a
Explanation: A Transformer is a device used to convert low alternating voltage to a high alternating voltage and vice versa. Transformers are based on the phenomena of mutual induction.
2. What is the working principle of a Transformer?
a) Transformer works on the principle of self-induction
b) Transformer works on the principle of mutual induction
c) Transformer works on the principle of ampere law
d) Transformer works on the principle of coulomb law
Answer: b
Explanation: A transformer is an electrical device used to vary the input voltage. Transformer works on the principle of mutual induction.
3. What is the function of a transformer?
a) Transformer is used to step down or up the AC voltages and currents
b) Transformer is used to step down or up the DC voltages and currents
c) Transformer converts DC to AC voltages
d) Transformer converts AC to DC voltages
Answer: a
Explanation: A Transformer does not work on DC and operates only on AC, therefore it Steps up or Steps down the level of AC Voltage or Current, by keeping the frequency of the supply unaltered on the secondary side.
4. Which of the following is not a part of transformer installation?
a) Breather
b) Conservator
c) Exciter
d) Buchholz relay
Answer: c
Explanation: The conservator, breather, and Buchholz relay are the parts that are much important in transformer construction in order to maintain the temperature of the transformer and to work the transformer with good efficiency.
5. Transformer core is generally made of ___________
a) Cannot be determined
b) Can be made with any of the above methods
c) By stacking a large number of sheets together
d) Single block of core material
Answer: c
Explanation: The transformer core experiences eddy current losses when the transformer is in the operation. In order to reduce eddy current losses, it is advisable to use a large number of sheets laminated from each other that are stuck together than using one single block.
6. Transformer ratings are given in ____________
a) kVA
b) HP
c) kVAR
d) kW
Answer: a
Explanation: There are two types of losses in a transformer, Copper Losses, and Iron Losses or Core Losses or Insulation Losses. Copper losses (I2R) depend on the current passing through transformer winding while Iron losses or Core Losses or Insulation Losses depend on Voltage. That’s why the rating of Transformer is in kVA.
7. Current transformers are __________________
a)parallel connected type of instrument transformers
b)series connected type of instrument transformers
c) parallel-connected normal transformers
d) series-parallel connected type of instrument transformers
Answer: b
Explanation: Current transformer (CT) is a series-connected type of instrument transformer. They are designed to present negligible load to the supply which is being measured and also have an accurate current ratio and phase relationship to enable accurate secondary connected metering.
8. The purpose of the transformer core is to provide ____________
a) Low reluctance path
b) High inductive path
c) High capacitive path
d) High reluctance path
Answer: a
Explanation: The purpose of a transformer core is to provide a low-reluctance path for the magnetic flux linking primary and secondary windings. In doing so, the core experiences iron losses due to hysteresis and eddy currents flowing within it which, in turn, show themselves as heating of the core material.
9. What is the thickness of laminations used in a transformer?
a) 14 mm to 15 mm
b) 25 mm to 40 mm
c) 0.1 mm to 0.5 mm
d) 4 mm to 5 mm
Answer: c
Explanation: Laminations are made to reduce the eddy currents and is made of thin strips. Generally, the steel transformer lamination range for 50 Hz varies from 0.25mm to 0.5mm, if it is a 60 Hz transformer then it ranges from 0.17–0.27mm.
10. Transformers are generally designed for ___________
a) one-time use
b) off-site problem solving
c) short-time use
d) on-site problem solving
Answer: d
Explanation: Every transformer is designed for use for multiple years, thus transformers are designed to handle the problems on-site because it not only saves time but also makes repairing work easy.
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11. Primary winding of a transformer ______________
a) Could either be a low voltage or high voltage winding
b) Is always a high-voltage winding
c) Cannot be determined
d) Is always a low-voltage winding
Answer: a
Explanation: Primary winding used in a transformer, can be at higher or lower voltage potential, depending on the number of turns with the secondary winding. For step-up and step-down transformers, the primary winding will be at lower and higher potential respectively.
12. Which type of flux does transformer action need?
a) Alternating electric flux
b) Alternating magnetic flux
c) Increasing magnetic flux
d) Constant magnetic flux
Answer: b
Explanation: The energy transfer in a transformer, is from one winding to another, entirely through a magnetic medium it is known as transformer action. Therefore, transformer action requires an alternating or time-varying magnetic flux in order to transfer power from the primary side to the secondary side. Since induced emf in the winding is due to flux linkage.
13. What is the function of a breather in a transformer?
a) To arrest the flow of moisture when outside air enters the transformer
b) To cool the transformer oil
c) To provide oxygen inside the tank
d) To cool the coils during a reduced load
Answer: a
Explanation: Most of the power generation stations use silica gel breathers fitted to conservators of oil-filled transformers. The most used purpose of these silica gel breathers is to arrest the moisture when the outside air is sucked in by the transformer during the breathing process.
14. Which of the following transformer, Buchholz’s relay can be fixed on?
a) Welding transformers
b) Oil-cooled transformers
c) Auto-transformers
d) Air-cooled transformers
Answer: b
Explanation: Buchholz relay is used in transformers for protection against all kinds of faults. Buchholz relay is a famous and mostly used gas-actuated relay, which is installed to serve its best in oil-immersed transformers. It gives an alarm, via its electrical circuitry, if any fault occurs in the transformer.
15. Which transformer insulation material is best compared to Kraft paper?
a) Asbestos
b) Oil
c) Cotton
d) Low-grade pressboard
Answer: b
Explanation: Newly developed oil-filled transformers have capabilities much greater than those transformers which used Kraft paper as the dielectric material. Also, the electrical properties of Kraft paper depend on the physical and chemical properties of the paper.
16. An ideal transformer will have maximum efficiency at a load such that _____________
a) copper loss > iron loss
b) cannot be determined
c) copper loss = iron loss
d) copper loss < iron loss
Answer: c
Explanation: Maximum efficiency of a transformer is defined at that value when copper losses become completely equal to the iron losses. In all other cases, the efficiency will be lower than the maximum value.
17. Power transformers other than distribution transformers are generally designed to have maximum efficiency around ______
a) 10% overload
b) Near full-load
c) Half-load
d) No-load
Answer: b
Explanation: Similar to normal transformers power transformers are also designed to get maximum efficiency at a load that is near to the full load of a transformer specified. Only in the case distribution transformer, maximum efficiency is achieved at 60% of the full load.
18. Voltage regulation of transformer is given by _____________
a) V2-E2/E2
b) V2-E2/V2
c) E2-V2/V2
d) E2-V2/E2
Answer: d
Explanation: Voltage regulation is defined as the change in the voltage or rise in voltage when a transformer load is thrown off. Thus, it is the difference of the no-load voltage with the full load voltage divided by the full load voltage to get a % increase.
19. Which of the following is the main advantage of an auto-transformer over a two-winding transformer?
a) Eddy’s losses are totally eliminated
b) Copper losses are negligible
c) Saving in winding material
d) Hysteresis losses are reduced
Answer: c
Explanation: Auto-transformer is a special type of transformer that has primary and secondary winding both located on the same winding. Thus, the winding material required for a transformer is very less in the case of an autotransformer.
20. No-load current in the transformer is ______
a)low noise levels
b) TTL compatibility
c) lower input impedance
d) faster operation
Answer: a
Explanation: The no-load current in a transformer is non-sinusoidal. The basic cause for this phenomenon, which lies in hysteresis and saturation non-linearities of the core material, will now be investigated; this can only be accomplished graphically.
21. When the secondary of a current transformer is open-circuited its iron core will be
a) Hot because of heavy iron losses taking place in it due to high flux density
b) Hot because primary will carry the heavy current
c) Cool as there is no secondary current
d) None of the above will happen
Answer: a
22. The hum in a transformer is mainly attributed to
a) Load changes
b) Oil in the transformer
c) Magnetostriction
d) Mechanical vibrations
Answer: c
23. Transformer breaths in when
a) Load on it increases
b) Load on it decreases
c) Load remains constant
d) None of the above
Answer: b
24. The dielectric strength of transformer oil is expected to be
a) 1 kV
b) 33 kV
c) 100 kV
d) 330 kV
Answer: b
25. In a transformer, the tapings are generally provided on
a) Primary side
b) Secondary side
c) Low voltage side
d) High voltage side
Answer: c
26. Gas is usually not liberated due to the dissociation of transformer oil unless the oil temperature exceeds
a) 50°C
b) 80°C
c) 100°C
d) 150°C
Answer: d
27. The material used for the construction of the transformer core is usually
a) Wood
b) Copper
c) Aluminium
d) Silicon steel
Answer: d
28. The mutual inductance when k= 0.65, L1= 2 μH, and L2 = 5 μH is
a) 2 mH
b) 2 μH
c) 4 μH
d) 8 μH
Answer: b
29. What kVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV?
a) 4 kVA
b) 25 kV
c) 16 kVA
d) 8 kVA
Answer: c
30. A transformer consists of two or more cores that are electrically coupled on a common core.
a) True
b) False
Answer: b
31. If the voltage is stepped up, the current is stepped down, and vice versa.
a) True
b) False
Answer: a
32. A transformer oil must be free from
a) Sludge
b) Odour
c) Gases
d) Moisture
Answer: d
33. Helical coils can be used on
a)Low voltage side of high kVA transformers
b) High-frequency transformer
c)High voltage side of small capacity transformers
d) High voltage side of high kVA rating transformers
Answer: a
34. A transformer with a 110 V primary has a 15:1 turns ratio. The load resistance, RL, is 120 Ω. What is the approximate voltage across the load?
a) 3 V
b) 73 V
c) 88 V
d) 880 V
Answer: a
35. When a 200 Ω load resistor is connected across the secondary winding of a transformer with a turns ratio of 4, the source “sees” a reflective load of
a) 50 Ω
b) 5 Ω
c) 800 Ω
d) 0 Ω
Answer: b
36. If the supply frequency to the transformer is increased, the iron loss will
a) No change
b) Decrease
c) Increase
d) Any of the above
Answer: c
37. Natural air cooling is generally restricted for transformers up to
a) 5 MVA
b) 5 MVA
c) 15 MVA
d) 50 MVA
Answer: a
38. The turns ratio required to match an 80 Ω source to a 320 Ω load is
a) 80
b) 20
c) 4
d) 2
Answer: d
39. Good voltage regulation of a transformer means
a) Output voltage fluctuation from no load to full load is least
b) Output voltage fluctuation with power factor is least
c) Difference between primary and secondary voltage is least
d) Difference between primary and secondary voltage is maximum
Answer: a
40. In a certainly loaded transformer, the secondary voltage is one-fourth the primary voltage. The secondary current is
a) One-fourth of the primary current
b) Four times the primary current
c) Equal to the primary current
d) One-fourth of the primary current and equal to the primary current
Answer: b
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