Here are 1000 Transformer MCQ (Chapterwise).
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 voltage
View Answer
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. A transformer consists of a soft iron coil with two coils wound around it which are not connected to one another.
2. 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
View Answer
Explanation: A Transformer does not work on DC and operates only on AC, therefore it Step up or Step down the level of AC Voltage or Current, by keeping frequency of the supply unaltered on the secondary side.
3. 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
View Answer
Explanation: A transformer is an electrical device used to vary the input voltage. Transformer works on the principle of mutual induction.
4. Transformer ratings are given in _____________
a) kVA
b) HP
c) kVAR
d) kW
View Answer
Explanation: There are two types of losses in a transformer, Copper Losses and Iron Losses or Core Losses or Insulation Losses. Copper losses (I2R) depends on current passing through transformer winding while Iron losses or Core Losses or Insulation Losses depends on Voltage. That’s why the rating of Transformer is in kVA.
5. What is the current transformer?
a) transformer used with an A.C. voltmeter
b) transformer used with an A.C. ammeter
c) transformer used with an D.C. voltmeter
d) transformer used with an D.C. ammeter
View Answer
Explanation: A transformer used to extend the range of an A.C. ammeter is known as a current transformer. A current transformer is also abbreviated as C.T.
6. 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
View Answer
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.
7. Which of the following is not a part of transformer installation?
a) Breather
b) Conservator
c) Exciter
d) Buchholz relay
View Answer
Explanation: Conservator, breather, Buchholz relay are the parts which are much important in transformer construction in order to maintain temperature of the transformer and to work transformer with good efficiency.
8. Transformer core is generally made of ___________
a) Cannot be determined
b) Can be made with any of the above method
c) By stacking large number of sheets together
d) Single block of core material
View Answer
Explanation: Transformer core experiences eddy current losses when transformer is in the operations. In order to reduce eddy current losses, it is advisable to use large number of sheets laminated from each other are stick together than using one single block.
9. 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
View Answer
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.
10. Transformers are generally designed for ___________
a) one-time use
b) off-site problem solving
c) short-time use
d) on-site problem solving
View Answer
Explanation: Every transformer is designed for use it for multiple years, thus transformers are designed to handle the problems on site itself because it not only saves time but also makes repairing work easy.
11. 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
View Answer
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.
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
View Answer
Explanation: The energy transfer in a transformer, is from one winding to another, entirely through 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 primary side to secondary side. Since induced emf in the winding is due to flux linkage.
13. 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
View Answer
Explanation: Primary winding used in a transformer, can be at higher or lower voltage potential, depending on the number of turns with secondary winding. For step up and step-down transformers primary winding will be at lower and higher potential respectively.
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
View Answer
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. What is the function of a breather in a transformer?
a) To arrest 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 reduced load
View Answer
Explanation: Most of the power generation stations use silica gel breathers fitted to conservator 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.
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
View Answer
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. Which transformer insulation material is best compare to Kraft paper?
a) Asbestos
b) Oil
c) Cotton
d) Low grade pressboard
View Answer
Explanation: Newly developed oil-filled transformers have capabilities much greater than those transformers which used Kraft paper as dielectric material. Also, electrical properties of Kraft paper depend on physical and chemical properties of paper.
18. For a transformer with primary turns 400, secondary turns 100, if 20A current is flowing through primary, we will get ___________
a) 800A at secondary
b) 40A at secondary
c) 80A at secondary
d) 5A at secondary
View Answer
Explanation: Current in the primary of the transformer will get modified in the transformer secondary, according to the number of turns, in inverse proportion. Thus, turns are modified with 1/4 times the primary, we’ll get 4 times higher current at secondary.
19. A 25 KVA transformer is constructed to a turns ratio of N1/N2 = 10. The impedance of primary winding is 3+j5 ohms and of secondary winding is 0.5+j0.8 ohms. What will be the impedance of transformer when referred to primary?
a) 53 + 85j ohms
b) 53j + 85 ohms
c) Can’t be calculated
d) 3.5 + 5.8j ohms
View Answer
Explanation: Given turns ratio is 10. Thus, secondary resistance when referred to the primary is equal to k2*Z2, so net impedance on primary is equal to primary impedance + k^2*Z2 . Substituting all the terms we get net impedance = 53 + 85j ohms.
20. The full-load copper loss of a transformer is 1600 W. At half-load, the copper loss will be _______
a) 1600 W
b) 6400 W
c) 400 W
d) 800 W
View Answer
Explanation: Copper losses are defined as I2*R losses many times, as they are directly proportional to the square of current flowing through them. Thus, copper losses will reduce if load is reduced that too in square proportion.
21. 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
View Answer
Explanation: Similar to normal transformers power transformers are also designed to get maximum efficiency at load which is near to the full load of a transformer specified. Only in the case distribution transformer maximum efficiency is achieved at 60% of full load.
22. For a power transformer operating at full load it draws voltage and current equal to 200 V and 100 A respectively at 0.8 pf. Iron and copper losses are equal to 120 kW and 300kW. What is efficiency?
a) 97.44%
b) 99.12%
c) 86.44%
d) 96.44%
View Answer
Explanation: Power output= VI cosθ= 200*100*0.8 = 16000 W (Independent of lag and lead). While total losses are equal to iron loss+ k2*copper losses =120+ 300= 420 W. Efficiency is equal to 1- 420/(16000+420)= 97.44%.
23. Voltage regulation of transformer is given by _____________
a) V2-E2/E2
b) V2-E2/V2
c) E2-V2/V2
d) E2-V2/E2
View Answer
Explanation: Voltage regulation is defined as change in the voltage or rise in voltage when transformer is load is thrown off. Thus, it is the difference of the no load voltage with the full load voltage divide by full load voltage to get % increase.
24. No-load current in the transformer is _______
a) Sinusoidal distorted
b) Sinusoidal
c) Steps
d) Straight DC
View Answer
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.
25. Which of the following is the main advantage of an auto-transformer over a two-winding transformer?
a) Eddy losses are totally eliminated
b) Copper losses are negligible
c) Saving in winding material
d) Hysteresis losses are reduced
View Answer
Explanation: Auto transformer is a special type of transformer which has primary and secondary winding both located on same winding. Thus, winding material required for a transformer is very less in the case of autotransformer.
26. For a 20kVA transformer with a turn ratio of 0.4 what amount of total power is transferred inductively?
a) 10kVA
b) 8kVA
c) 50kVA
d) 12kVA
View Answer
Explanation: For an auto transformer power is transferred partially inductively and partially conductively. Thus, out of total power, power transferred inductively is given by (1-k)*total power= 0.6*20= 12kVA.
27. Which of the following is the major requirement for the transformers used for electronic purposes?
a) Constant amplitude voltage gain
b) Perfect DC isolation, maximum efficiency and constant voltage gain
c) Perfect DC isolation
d) Maximum efficiency
View Answer
Explanation: An important requirement of these transformers is that the amplitude voltage gain (ratio of output/input voltage amplitude) should remain almost constant over the range of frequencies (bandwidth) of the signal.
28. Which type of winding is used in 3-phase shell-type transformer?
a) Cylindrical type
b) Circular type
c) Rectangular type
d) Sandwich type
View Answer
Explanation: In core type of the transformer, winding is done by normal method, while in the shell type transformer, winding is sandwiched between corresponding shells of core material. Hence, it is sandwich type.
29. Why shell type 3-phase transformer is used in large power transforming applications?
a) Due to other reasons
b) More height and less height flexibility
c) Can be made with less height
d) Can be made with more height
View Answer
Explanation: The shell-type five-limb type three-phase transformer construction is heavier and more expensive to build than the core-type. Five-limb cores are generally used for very large power transformers as they can be made with reduced height.
30. Which of the following is not a routine test for transformers?
a) Polarity test
b) Radio interference test
c) Core insulation voltage test
d) Impedance test
View Answer
Explanation: Impedance test is done on a transformer in order to check net impedance offered by a transformer circuit at rated supply. Polarity test is also done before SC and OC test on transformer. Core insulation is also checked before installations in such tests.
31. What will happen if the secondary of a current transformer is open-circuited?
a) depends on other parameters
b) cool as there is no secondary current
c) hot because primary will carry heavy current
d) hot because of heavy iron losses
View Answer
Explanation: If secondary of current transformer is made open-circuited the transformer temperature will rise to higher value because of heavy iron losses taking place in the circuit due to high flux density.
32. Welding transformers work on principle that weld is actually __________________
a) open circuit
b) short circuit
c) circuit with finite resistance
d) circuit with finite reactance
View Answer
Explanation: The increase in primary or secondary current of welding transformer increases the reactance voltage drop across the respective windings, which is essential to limit the welding current as the weld is practically a short circuit.
33. Insulation of HVDC transformers should be ___________
a) no need of insulation
b) can be dry or wet
c) wet always
d) dry always
View Answer
Explanation: Because of the effect of moisture on the resistivity of insulation material, it is necessary to obtain and maintain a high level of dryness in the insulation of HVDC transformers. This is equally important in service as it is in the factory at the time of testing.
34. Core flux in the transformer is _______________
a) square wave
b) triangular
c) sinusoidal
d) flat-topped
View Answer
Explanation: The supply voltage provides the input current to the transformer primary, here primary current is only sinusoidal magnetizing current. Thus, this sinusoidal magnetic current will produce core flux, flat-topped.
35. For a transformer with primary turns 100, secondary turns 400, if 200 V is applied at primary we will get ___________
a) 3200 V at secondary
b) 1600 V at secondary
c) 800 V at secondary
d) 80 V at secondary
View Answer
Explanation: Voltage in the primary of the transformer will get modified in the transformer secondary, according to the number of turns. Thus, turns are modified with 4 times the primary, we’ll get 4 times higher voltage at secondary.
36. For a transformer given of 100 kVA, 220/6000-V transformer, short circuit test is performed. What current rating is needed?
a) 445A
b) 40A
c) 60A
d) 30A
View Answer
Explanation: For a given transformer here, test is performed on low voltage side, thus we need the value of current on the low voltage side, by dividing the reactive power by the rated voltage value, i.e. 200*1000/100 = 445A.
Chapterwise Multiple Choice Questions on Transformer
- Basic Materials & Transformer Construction
- Transformers
- Real Transformer and Equivalent Circuit
- Transformer Losses & Testing
- Efficiency and Voltage Regulation
- Excitation Phenomenon & Variable Frequency Transformers
- Three Phase Transformers
- Parallel Operation of Transformers
- Three Winding Transformers
- Phase Conversion & Tap Changing Transformers
- Voltage, Audio Frequency & Grounding Transformers
- Transformer Operation and Maintenance
- Special Features of Transformer for Special Purposes
1. MCQ on Basic Materials & Transformer Construction
The section contains Transformer multiple choice questions and answers on transformer basic materials and construction.
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2. Multiple Choice Questions on Transformers
The section contains questions and answers on transformers load operations, transformer cooling techniques and ideal transformer.
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3. MCQ on Real Transformer and Equivalent Circuit
The section contains MCQs on real transformer and equivalent circuit, approximate circuit and models.
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4. Multiple Choice Questions on Transformer Losses & Testing
The section contains multiple choice questions and answers on transformer losses, sumpner’s test, transformer oc and sc tests.
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5. Transformer MCQ on Efficiency and Voltage Regulation
The section contains Transformer questions and answers on efficiency and voltage regulation.
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6. Multiple Choice Questions on Excitation Phenomenon & Variable Frequency Transformers
The section contains MCQs on excitation phenomenon, autotransformer and variable frequency transformer.
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7. MCQ on Three Phase Transformers
The section contains multiple choice questions and answers on three phase transformer construction and connections, three phase bank of single phase transformer and three phase transformer tests.
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8. Multiple Choice Questions on Parallel Operation of Transformers
The section contains questions and answers on transformers additional testing, transformer installations and parallel operations.
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9. MCQ on Three Winding Transformers
The section contains MCQs on three winding transformers.
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10. Multiple Choice Questions on Phase Conversion & Tap Changing Transformers
The section contains multiple choice questions and answers on phase conversion and tap changing transformers.
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11. MCQ on Voltage, Audio Frequency & Grounding Transformers
The section contains questions and answers on voltage and current transformers, transformers as magnetically coupled circuits, audio frequency transformer, grounding and welding transformers.
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12. Multiple Choice Questions on Transformer Operation and Maintenance
The section contains Transformer MCQs on neutral earthing and noise, abnormal conditions, transformer protection and maintenance.
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13. MCQ on Special Features of Transformer for Special Purposes
The section contains Transformer multiple choice questions and answers on generator and power station transformers, hvdc conversion and distribution transformers.
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Wish you the best in your endeavor to learn and master Transformer!
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