Transformer MCQsMarch 15, 2021 By WatElectronics This article lists 100 Transformer MCQs for engineering students. All Transformer Questions & Answers given below include a hint and wherever possible link to the relevant topic. This is helpful for users who are preparing for their exams, interviews, or professionals who would like to brush up their fundamentals on Transformers topic which is core in Electronics & Electrical Engineering.A transformer is a static device, which works on the principle of Faraday’s law of electromagnetic induction. The basic functionality of a transformer is to transfer electrical energy from one circuit to another. It mainly consists of two windings namely primary and a secondary winding, based on the number of turns on either side of windings, the transformer is classified into two types step up and step-down transformer. If the number of turns is more on the secondary winding of a transformer it is called a step-up transformer and if the number of turns is more on the primary winding of a transformer it is called a step-down transformer.Transformers are further classified based on their voltage levels used, the type of core used, the number of windings used, etc. The merits and demerits of a transformer are it operates with higher efficiency and occupies more space with high maintenance cost. Some of the applications of a transformer are regulators, power supply appliances, voltage converter. Transformer Multiple Choice Question & Answers 1). Transformer works on ______ principle.a) Gauss’s lawb) Fleming’s right-hand rulec) Faraday’s law of electromagnetic inductiond) Fleming’s left-hand ruleHint- Faraday’s law of electromagnetic induction states that the magnitude of voltage is directly proportional to the rate of change of flux 2). A step-up transformer has _____ number of turns on primary winding and _____ number of turns on secondary winding.Add description here!Less, MoreMore, MoreMore, LessLess, LessHintA step-up transformer has more secondary winding than primary windings, this increases the voltage from the primary to the secondary side of the transformer. 3). A step-down transformer has _____ number of turns on primary winding and _____ number of turns on secondary winding.Less, MoreMore, LessMore, MoreLess, LessHintA step-down transformer has less secondary winding than primary windings, this decreases the voltage from primary to secondary. 4). A transformer is a _____ device.StaticDynamicStatic and DynamicNone of the aboveHintA transformer is a static electrical machine that transfers AC electric power from one circuit to another circuit at a constant frequency. 5). In a current transformer _____ winding is closed.PrimarySecondaryBoth a & bNone of the aboveHintIn a current transformer, the secondary winding is closed, to protect the insulation of a transformer from generating a high voltage across the secondary winding. 6). In a transformer the relation between the input frequency and the output voltage on secondary winding is _____.SameIncreasesDecreasesIncreases and decreases with timeHinthe relation between the input frequency and the output voltage on secondary winding are the same. A transformer is a static device, that has voltage fluctuation in its primary winding and secondary winding at a constant frequency due to the mutual induction property. 7). The efficiency of a power transformer is _____ at full load.SameMinimumMaximumFluctuatesHintPower transformers act as a step-up device that operates with maximum efficiency at full load conditions with negligible load fluctuation. 8). Copper losses in a transformer are measured using _____.Closed circuitOpen circuitBoth a & bNone of the above.HintWhen a transformer is open-circuited the current in load is very less, and so copper losses can be neglected. 9). Transformer core lamination is made up of _____.Silicon steelCast steelCast ironAluminiumHintSilicon steel is used in the cores of electrical devices like transformers due to its properties like low Hysteresis loss, permittivity is high, resistance is high, aging of metal. 10). What is the functionality of a breather in a transformer?It absorbs the moisture of air during breathingPasses cold air to the transformerIt is the transformer oil filterBoth a & bHintBreather helps in absorbing the moisture of air during the breathing process while the transformer is operating. 11). What is basic functionality of a transformer?Voltage to current converterCurrent to voltage converterFrequency converterNone of the aboveHintThe transformer is a static device that converts current or voltage to a lower or a higher level 12). What are the two types of Instrument transformer?Voltage transformerCurrent transformerPotential transformerBoth b and cHintInstrument transformers are classified into 2 types they are current transformer and potential 13). The core of a transformer is laminated for _____ reasonMinimize hysteresis lossMinimize eddy & hysteresis current lossLowers eddy current lossCopper lossHintThe eddy current loss in a transformer is directly proportional to the square of the diameter of the core. Hence the core of a transformer is laminated so that it minimizes the net effective diameter of the transformer core and eddy current loss. 14). The voltage regulation in a transformer is said to be negative when the load power factor is _____.IdealLagsLeadsInfinityHintThe voltage regulation in a transformer is said to be negative when the load power factor is leading. This condition can be observed when secondary voltage increases with an increase in load current. 15). What is the need of performing a short circuit test in a transformer?To find copper lossTo find core lossTo find insulation resistanceTo find complete lossHintA short circuit test is performed to find copper losses in a transformer. This test is usually done on the higher voltage side of a transformer winding to get an accurate value. 16). Which losses in a transformer is zero at full load?Core lossEddy current lossCopper lossFriction lossHintA transformer is a static device which has zero friction loss at full load condition. 17). A transformer has _____ resistance between its primary and secondary winding.Infinity00.1 ohm100 ohmHint In an ideal transformer, there is no electrical contact between the coils hence the transformer has infinite resistance between primary and secondary windings. 18). The current rating of a transformer is expressed as_____.KilowattsKVARKilo-volt-ampereAmpereHintThe current rating of a transformer is expressed in terms of kilo-volt-ampere. 19). What is the purpose of oil in an oil-filled transformer?InsulateResistanceCoolingBoth a & dHintThe main function of oil in an oil-filled transformer is to provide insulation and cooling to the transformer. Coolant: When a very high current flows through the copper coil of a transformer making the coil hot. At this stage transformer oil act as a coolant in reducing the temperature of the coil. Insulator: The dielectric property of transformer oil makes the transformer to act as an insulator by withstanding high voltage. 20). Which test is used to determine iron losses in a transformer?SC testOC testBoth SC & OCNone of the aboveHintOpen circuit test or no-load test is used to determine iron losses in a transformer. 21). Which of the following component is not related to the transformer?BreatherConservatorBuchholz relayExciterHintAn exciter is a component used in an electric motor, which is used to kick start a motor. 22). Which component of the transformer causes noise?Vibration due to mechanical motionFan that is used for cooling purposeIron core which contains magnetostrictionAll the aboveHintWhen the core transformer is laminated with iron, it may exhibit a change in its shape when a magnetic field is applied, this process is called the magnetostrictive effect 23). The relation between primary and secondary flux in a transformer is ________.Primary is greater than the secondary fluxPrimary flux is less than the secondary fluxPrimary flux and secondary flux are equalNone of the aboveHintThe value of the main flux in a transformer remains constant due to an increase in permeability and greater mutual flux value. The relationship between primary flux and secondary flux can be understood based on the load used, in other words, if load increases, more current is drawn by primary and secondary winding which demagnetize the core. Thereby maintaining equal primary and secondary flux values. In the case where the value of load reduces the value of primary and secondary current reduces. 24). If the direct current is supplied to a transformer, what happens to a transformer.Transformer operates normallyTransformer operates with greater efficiencyTransformer operates with low efficiencyTransformer stops working due to damage that occurredHintThe transformer has primary and secondary winding, where supplying DC supply high current value to the primary winding that has less resistance value would damage the winding. This results in the non-functioning of a transformer. 25). How much percent of friction loss is present in a transformer?1%3%0%5%HintSince the transformer is a stationary device, which has zero movable parts. Hence it has 0% of frictional loss.Transformer Interview Questions 26). Which transformer has primary and secondary winding coupled electrically and magnetically?Power transformerCurrent transformerPotential transformerAuto transformerHintAn auto transformer has a single winding which is used as both primary and secondary winding, which is electrically and magnetically coupled. 27). What is the purpose of stones in a transformer?To provide InsulationTo safeguard from fire accident if there was an oil leakage in a transformerTo prevent the growth of weeds and plantAll the aboveHintStones are provided, to protect or insulate the transformer from fire accident which usually occurs during oil leakage. The moister that is present due to the growth of weeds or plants in a transformer will not only damage the transmission lines but also leaks the current in the circuit. The growth of plants and weeds can be eliminated by using stones. 28). What is the reason behind the cruciform shape of a transformer?Decrease in core lossDecrease in the reluctance of the coreDecrease in copper windingAll the aboveHintCruciform shape in a transformer not only reduces the core loss but also reduces the reluctance value of the core and the number of windings in copper. 29). Which losses are neglected when a transformer undergoes a short circuit test?Copper lossesCore lossEddy current lossHysteresis lossHint When a low input voltage is applied to the primary windings and increased along with increasing the value of load from 0 to maximum. The current in the ammeter shows the full load current value. Hence core losses can be neglected. 30). The volatility and viscosity values of an oil transformer should be _________.High, LowLow, HighLow, LowHigh, HighHintVolatility in other terms is the vaporization of a substance at a given temperature. where at a given temperature, a substance vaporizes quickly at high pressure. Hence the volatility value should be less, Viscosity is used to measure how much resistance the fluid is flowing, hence lower the value of viscosity greater will be the fluidity which cools down the temperature of a transformer. 31). On which parameter does the core size of a transformer depends?Cores area and frequencyOnly core areaOnly frequencyNone of the aboveHintThe EMF equation of a transformer is given as E = 4.4fNAB; Where E = Voltage F = Frequency A = cores area B = magnetic flux density When the values E, N, B are made constant and the value of frequency is increased then the value of the cores area decreases. This results in a reduction of transformer size. 32). Formula to calculate the number of turns ratio in a transformer is given as_____.Number of turns of secondary / Number of turns of the primaryNumber of turns of primary / Number of turns of secondaryNumber of turns of secondary aloneNumber of turns of primary aloneHintThe number of turns present in a transformer can be calculated using the Number of turns of primary / The number of turns of secondary, this ratio is called turns ratio. The input winding is called primary winding and the output winding is called secondary winding. 33). Formula for primary voltage of a transformer is _________.Primary voltage (Vp)*turns ratio (n)Secondary voltage (Vs)* turns ratio (n)Primary voltage(Vp) * efficiencyPrimary voltage(Vp) * secondary voltage(Vs)HintPrimary voltage of a transformer = secondary voltage * turns ratio If a greater number of turns are present on the primary side than the secondary side of a transformer, the output voltage will be less than the input voltage. It is also called a step-down transformer 34). Formula for secondary voltage of a transformer is _________.Primary voltage (Vp)/turns ratio (n)Secondary voltage (Vs)* turns ratio (n)Primary voltage(Vp) * efficiencyPrimary voltage(Vp) * secondary voltage(Vs)HintThe secondary voltage of a transformer = Primary voltage (Vp)/turns ratio (n) If less number of turns are present on the primary side than the secondary side of a transformer, the output voltage will be greater than the input voltage. It is also called a step-up transformer. 35). The phase angle of an ideal transformer is ________.ΦP ≡ ΦSΦp > φsΦp < φsΦp != φsHintAn ideal transformer has an equal phase given as ΦP ≡ ΦS. 36). What is a dual voltage transformer?A transformer with a single primary and single secondary windingsA transformer with two primaries and two secondary windingsA transformer with single primary and dual secondary windingsNone of the aboveHintA transformer with two primary and two secondary windings is called a dual voltage transformer. It provides two types of voltages based on the pattern they are connected to like if the two windings are connected in series it gives the sum of two supplied coil voltages and if two coils are connected in parallel, there will be a decrease in total output voltage. 37). Which of the following is the advantage of a transformer?It is a stationary deviceIt provides high efficiencyNo starting time is requiredAll the aboveHintThe transformer provides the following advantages it is a stationary device that has no moving parts, it provides a high-efficiency output and it does not need any starting time. 38). Which of the following is the disadvantage of a transformer?It is a stationary deviceIt is a bulky deviceSize and voltageBoth b and cHintThe disadvantage of a transformer is, it is a bulky device that occupies a large area and requires high input voltage. 39). What are the types of cores in a transformer?Core TypeShell typeIdeal typeBoth a and bHintA transformer can have any one type of cores that is either core type or shell type. These shells can be distinguished based on the position of the coil around the steel core. In a core-type transformer, the windings are wounded outside and surrounded the core winding.Whereas in a shell type transformer, the windings pass inside the core which forms a shell around the windings. 40). Which test is performed to find the temperature of a transformer?Open load testClose load testSumpner’s testNone of the aboveHintA Sumpner test is performed to known the temperature value of a transformer. It is also called as back to back test or regenerative test. 41). The maximum efficiency of a transformer can be observed at _____ condition.Maximum Iron lossMinimum core lossCopper loss and iron loss are equalHysteresis lossHintThe maximum efficiency of a transformer can be observed when copper loss and iron loss are equal. 42). What is the maximum range the natural oil cooling can be used in a transformer?50kVA3000kVA500 kVA250kVAHintThe maximum range the natural oil cooling can be used in a transformer is 3000kVA. 43). What is the equivalence resistance relationship between the primary and secondary winding of a transformer?R2/VIR2/K2R2R1HintThe equivalence resistance relationship between the primary and secondary winding of a transformer is given as R2/K2 where R2 is the secondary winding resistance and K is the turns ratio. 44). On which side of transformer tapings are provided in general?Secondary sideRight sideLow voltage sidePrimary sideHintTapings are provided on the low voltage side of the transformer. These are provided to adjust the turn ratio to compensate power supply. 45). Which substance is used in the transformer breather component?Silica gelSodiumSilica sandPotassiumHintSilica gel is a substance that is used in transformer breather component, which prevents the growth of unnecessary plants or weeds on a transformer. 46). What is the value of inductance in an ideal transformer?0Infinity100%50%HintThe value of inductance in an ideal transformer is infinity. 47). Give the equation of hysteresis loss in a transformerCBmax= BmaxCBmax=Bmax 1-6CBmax=0None of the aboveHintThe equation of hysteresis loss in a transformer is CBmax=Bmax 1-6 48). The core of a transformer is constructed using ________.WoodZincSteelSilicon steelHintThe core of a transformer is constructed using silicon steel which has high permeability property. 49). What is the purpose of a conservator in a transformer?Protects against short circuitPrevents moisture entryControls the transformer oil which expands and contracts based on environmental temperatureNone of the aboveHintThe purpose of a conservator in a transformer is to control the transformer oil which expands and contracts based on environmental temperature. 50). The lamination thickness of a transformer is______.0.4 mm to 0.5 mm0.1mm to 0.2 mm2.5 mm to 5 mm6 mm to 8 mmHintThe lamination thickness of a transformer is 0.4 mm to 0.5 mm.Transformer Questions and Answers 51). The oil used in a transformer must be free from______.SandOdourMoisterSludgeHintThe oil used in a transformer must be free from moisture. 52). On which transformer can we install the Buchholz relay?Power transformerMechanical transformerOil cooled transformerWelding transformerHintBuchholz relay is installed on the oil-cooled transformer, this relay protects the transformer from short circuits and other faults from happening. 53). Why do harmonics occur in a transformer?Short circuitBreak downLess insulationcore getting saturatedHintHarmonics occur in a transformer due to saturation of the core. 54). What is the efficiency of the distribution transformer?100%50%10 %99%HintThe efficiency of the distribution transformer is 50%. 55). A transformer connected in star fashion works at ______ condition.No loadFull loadBalanced load and unbalanced loadBalanced loadHintA transformer connected in star fashion works at balanced load and unbalanced load conditions. 56). Buchholz relays warns about______.Electrical faults that occur within the transformerElectrical faults that occur in the surroundings of a transformerBoth a and bNone of the aboveHintBuchholz relays warn about the electrical faults that occur within the transformer. 57). Why transformers magnetized current is small?Due to little air gapDue to flux leakageDue to laminationNone of the aboveHintTransformer magnetized current is small due to little air gap. 58). Which parameter in a transformer remains the same?VoltageFrequencyResistanceAll the aboveHintThe frequency of a transformer is maintained constant at all conditions. 59). On which side helical coil in a transformer is placed?On less voltage side of a HkVA transformerPower transformerVoltage transformerIdeal transformerHintA helical coil in a transformer is placed on the less voltage side of a HkVA transformer. These coils are used to reduce eddy current loss. 60). Which test is least done on a transformer?Radio interface testOC testSC testNone of the aboveHintThe radio interface test is the least done on a transformer since it is done only on an RF transformer. 61). What happens if harmonics occur in a transformer?Core losses increasesI2R losses increasesBoth a and bNone of the aboveHintWhen harmonics occur in a transformer it increases Core losses and I2R losses increase. 62). Which type of core is used in a transformer with high frequency?CU coreCast Fe coreAir coreHintAir type core is used in a high-frequency transformer, whose function is to transfer radio frequency current. 63). The emf equation of a transformer has _____ value of flux.MaximumMinimumEqualZeroHintThe emf equation of a transformer has a maximum value of flux. 64). The purpose of Silicon steel in a transformer is to __________.Increase eddy current lossReduce hysteresis lossMaintain eddy current lossesNone of the aboveHintThe purpose of Silicon steel in a transformer is to reduce hysteresis loss. 65). Less cross-sectional area in a transformer can be observed on ________.Primary sideHigh voltage sideSecondary sideNone of the aboveHintThe less cross-sectional area in a transformer can be observed on the high voltage side. 66). At what conditions does power transformer has max efficiencyFull loadNo loadHalf loadNone of the aboveHint-At full load conditions, the power transformer has max efficiency of 98.5%. 67). What is the advantage of autotransformer over dual transformer?Low powerLess winding materialsHalf loadNone of the aboveHintThe advantage of autotransformer over dual transformer is that it uses less winding materials. 68). SI units of EMFVoltsAmperesHertzCentimetresHintSI units of EMF are Volts, which is equal to joule / Coulomb. 69). SI unit of powerWattHzCentimetresJouleHintSI unit of power is Watt (W). 70). Units of electric fieldVoltsAmperesVolts / MeterCentimetresHintThe electric field is measured in terms of volts per meter. 71). What is Np in a transformer?Number of turns on the primary windingNumber of turns on the secondary windingNumber of turns on both primary and secondary windingNone of the aboveHintNp in a transformer is a number of turns on the primary winding. 72). What is Ns in a transformer?Number of turns on the primary windingNumber of turns on the secondary windingNumber of turns on both primary and secondary windingNone of the aboveHintNs in a transformer is a number of turns on the secondary winding. 73). SI unit of magnetic field strengthVoltsAmperesAmp / MeterCentimetresHintSI unit of magnetic field strength is Amp / Meter 74). SI unit of Electrical FluxVolt MeterAmperesAmp / MeterCentimetresHintSI unit of Electrical Flux Volt Meter. 75). Faradays Law equationE = N dφ / dtE = N dφE = N dtN dφ = dtHintFaradays Law equation is given as E = N dφ / dt Where E = emf induced N= number of turns dφ / dt = change in flux with respect to time.Transformer Online Test 76). Transformers are classified based on __________.Core usedVoltage levelNumber of windingsAll the aboveHintTransformers are classified based on type core used - steel, iron, silicon, and other alloys Input voltage level - 240V , 330V the number of windings used on the primary side and on the secondary side. 77). Which of the following is the property of an ideal transformer?Absence of lossesAbsence of magnetic leakage10-ohm resistanceBoth a and bHintAn ideal transformer has zero losses and zero magnetic leakage. 78). When a transformer is operated at rated voltage and low frequency what happens?There will be an increase in core fluxIncrease in resistance valueIncrease in current valueNone of the aboveHintWhen a transformer is operated at rated voltage and low frequency, there will be an increase in core flux. 79). At what condition does an ideal transformer gives maximum efficiency?Copper loss = 0Copper loss = infinityCopper loss = iron lossCopper loss = 99%Hintan ideal transformer gives maximum efficiency when Copper loss = iron loss. 80). What happens to iron loss in a transformer, if there is an increase in input frequency?Add description here!0InfinityIncreasesDecreasesHintIn a transformer, if input frequency increases, the iron losses also increase. 81). If the negative voltage obtained from a load of a transformer, what does it mean?81) If the negative voltage obtained from a load of a transformer, what does it mean?Capacitive type loadInductive type loadResistive type loadNone of the aboveHintthe negative voltage obtained from a load of a transformer means the load is of capacitive type. 82). Transformer with a low power factor is used to measure _____ losses.Iron lossesSteel lossesEddy current lossesNone of the aboveHintA transformer with a low power factor is used to measure iron losses. 83). Which material is used between the transformer’s laminations?Mica stripVarnishOilHintThe material is used between the transformer’s laminations is thinly coated varnish, which prevents the moister from entering into transformers' windings. 84). A sandwich-type winding is used in which phase shell type transformer?Single phaseThree-phaseTwo-phaseZero phaseHintA sandwich-type winding is used in a three-phase shell type transformer, to balance magnetomotive force. 85). Why is the OC test is performed on the transformer?To find hysteresis lossTo find efficiencyTo find resistanceTo find core lossHintOC or no-load test is performed on the transformer to find the core loss. 86). Why is the SC test is performed on the transformer?To find copper lossTo find efficiencyTo find resistanceTo find core lossHintSC or full load test is performed on the transformer to find copper losses. 87). A single-phase transformer operating parallelly should maintain _________.Equal polarityOpposite polarityEqual efficiencyNone of the aboveHintA single-phase transformer operating parallelly should maintain equal polarity. 88). A transformer should have _____ volatility.LowEqualHighzeroHintA transformer should have low volatility. 89). A transformer should have _____ viscosity.LowEqualHighzeroHintA transformer should have low viscosity. 90). Which winding of the current transformer is short-circuited?primarysecondaryboth a and bnone of the aboveHintThe secondary winding of the current transformer is short-circuited because of the high fidelity property. 91). Natural air cooling property in a transformer is restricted _____ limit.0 MVA1 MVAUpto 1.5 MVA5 MVAHintNatural air cooling property in a transformer is restricted up to 1.5 MVA. 92). Which type of transformer has less magnetic leakage?Core typeShell typeBoth a and bNone of the aboveHintShell type transformer has less magnetic leakage. 93). A transformer operating at what condition it gives maximum efficiency at a unity power factor?Constant load currentConstant load voltageConstant frequencyZeroHintA transformer operating at constant load current gives maximum efficiency at a unity power factor. 94). Which material is used to withstand high temperatures in a transformer?SiliconSteelMicaGlassHintMica being a dielectric material is used to withstand high temperatures in a transformer. 95). Which component is visible from outside a transformer?WindingsCoreWiresBrushesHintBrushes are visible from outside a transformer. 96). What is the noise produced by a transformer called?HumZoomBuzzHuzzHintThe noise produced by a transformer called hum. 97). Why does hum occurs in the transformer?Due to full loadDue to no loadDue to magnetostrictionDue to the vibrationsHintHum occurs in the transformer due to the magnetostriction property, which changes the size of the core. 98). What happens to transformer windings if operated continuously?Temperature increasesTemperature decreasesResistance increasesNone of the aboveHintIf a transformer is operated continuously its winding temperature increases. 99). Which part of the transformer is damaged by overheating?CoreFrameWinding insulationBrushesHintWhen a transformer is overheated its winding insulation gets damaged. 100). What is the relationship between minimum voltage regulation and the power factor of the load?LagsLeadsZeroInfinityHintThe relationship between minimum voltage regulation and the power factor of the the load is that minimum voltage regulation leads the power factor of the load. Time is Up!