Transformer MCQ Online Test

1. In a 50 kVA transformer the number of turns in the primary and secondary windings are 834 and 58 respectively. If the primary is connected to 3300 V supply the secondary current will be

(a) 15 A
(b) 30 A
(c) 218 A
(d) 238 A


Answer: (c) 218 A
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2. If full load copper loss of a transformer is 800 W, its copper loss at 75% load will be

(a) 800 W
(b) 450 W
(c) 400 W
(d) 200 W


Answer: (b) 450 W
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3. The secondary of a current transformer is always short circuited under operating conditions because

(a) it avoids core saturation and high voltage induction
(b) it avoids high voltage surges
(c) it protects the primary circuit
(d) it is same for operation.


Answer: (a) it avoids core saturation and high voltage induction
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4. The main advantage of an autotransformer over a two winding transformer is that

(a) no cooling is required
(b) hysteresis losses are minimized
(c) eddy current losses are minimized
(d) only one winding is used as a result there is substantial saving in material


Answer: (d) only one winding is used as a result there is substantial saving in material
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5. If a break occurs in a 200 : 100 volt autotransformer in the winding which is common to high voltage as well as low voltage side, then the output voltage on the low voltage side will be

(a) 200 V
(b) 100 V
(c) 100√2
(d) zero


Answer: (a) 200 V
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6. In an autotransformer, effective saving on copper and copper loss will occur when the transformation ratio is

(a) more than 1
(b) nearly equal to 1
(c) less than 1
(d) 0.707


Answer: (b) nearly equal to 1
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7. Which of the following conditions should be full filled for the parallel operation of two transformers?

(a) percentage impedance should be the same
(b) polarities of both secondaries should be the same
(c) voltage ratings should be the same
(d) all of the above.


Answer: (d) all of the above.
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8. If the transformer core is made of copper

(a) copper losses will be less
(b) eddy current losses will be more
(c) hysteresis losses will be more.


Answer: (b) eddy current losses will be more
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9. If the secondary of a 5:1 step-down transformer is connected to the primary of 10:1 step-down transformer, the total step-down ratio of transformation will be

(a) 5 : 1
(b) 10 : 1
(c) 50 : 1
(d) 2500 : 1


Answer: (c) 50 : 1
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10. An engineer uses an ohmmeter to measure the DC resistance of a transformer winding. The engineer notices that, when one of the ohmmeter leads is disconnected from the transformer, a spark results. What accounts for this phenomenon?

(a) Ohm’s law
(b) Faraday’s law
(c) The Thomson effect
(d) The Seeback effect.


Answer: (b) Faraday’s law
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11. The efficiency of two identical transformers under load conditions can be determined by

(a) back to back test
(b) open circuit test
(c) short circuit test
(d) any of the above.


Answer: (a) back to back test
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12. Oil impregnated paper condenser bushing generally used on transformers operating at

(a) 11 kV
(b) 132 kV
(c) 33 kV
(c) 66 kV


Answer: (b) 132 kV
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13. If a transformer core is made of copper and coils are made up of steel wires, then

(a) magnetizing current will be reduced
(b) copper losses in the winding will be more
(c) eddy current loss will be less
(d) all of the above.


Answer: (b) copper losses in the winding will be more
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14. As a general rule, the kVA rating ratio of transformers operating in parallel should be within

(a) 2:1
(b) 3:1
(c) 4:1
(d) 5:1


Answer: (b) 3:1
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14. If the two transformers not having the same percentage impedances are connected in parallel for sharing a load then

(a) one of the transformer will be always fully loaded
(b) one of the transformer is likely to get burnt
(c) load sharing of the transformers will not be proportional to kVA ratings
(d) power factor of both the transformers will be lagging.


Answer: (c) load sharing of the transformers will not be proportional to kVA ratings
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16. Harmonic currents in a transformer cause

(a) increased I2R losses
(b) increased core losses
(c) all of the above.


Answer: (c) all of the above.
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17. Which of the following is the most likely source of harmonics in a transformer?

(a) over load
(b) core saturation
(c) poor insulation
(d) loose connections.


Answer: (b) core saturation
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18. A 100 W, 220 V incandescent bulb is connected in series with the primary of a 220 V, 20 kVA transformer. When the secondary of the transformer is open circuited, the bulb will

(a) not glow
(b) glow with less than normal brightness
(c) glow with normal brightness
(d) glow with more than normal brightness


Answer: (b) glow with less than normal brightness
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19. A tap changer is used on transformer for

(a) adjustments in primary voltage
(b) adjustments in secondary voltage
(c) adjustments in both primary and secondary voltage
(d) adjustments in power factor.


Answer: (b) adjustments in secondary voltage
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20. A 30/10 P 15 current transformer will have output of

(a) 30 VA
(b) 10 VA
(c) 15 VA
(d) 45 VA


Answer: (a) 30 VA
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21. In measuring voltage or current by means of instrument transformer …..

(a) only ratio errors need to be considered
(b) both ratio we well as phase angle error need to be considered
(c) either of the above
(d) none of the above


Answer: (a) only ratio errors need to be considered
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22.In order to find the full-load efficiency of a transformer the losses which must be known

(a) may be found by performing open-circuit and short-circuit tests
(b) may be found by measuring winding resistances and calculating the I2R losses
(c) may be found by measuring the input to the primary with secondary open
(d) cannot be found except by actually loading the transformer fully.


Answer: (a) may be found by performing open-circuit and short-circuit tests
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23. Which of the following statement concerning parallel operation of transformers is incorrect?

(a) Transformers must be operated at the same frequency
(b) Transformers must have same transformation ratio
(c) Transformers must have equal kVA
(d) Transformers must have equal voltage ratings


Answer: (c) Transformers must have equal kVA
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24. Current transformers for meters and relays usually have

(a) 1 : 2 ratio
(b) 5 : 1 ratio `
(c) 5-Asecondaries
(d) 15-A secondaries


Answer: (c) 5-Asecondaries
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25.All day efficiency is the ratio of output to input in

(a) kVA at a particular instant
(b) kW at particular instant
(c) kVARhat particular instant
(d) kWh during 24 hours


Answer: (d) kWh during 24 hours
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26. While performing back-to-back test, the amount of power consumed is equal to

(a) iron and copper losses of two transformers at full load
(b) full load rated output of the two transformers
(c) rated output of two transformers and iron and copper losses of transformers at full load
(d) none of the above


Answer: (a) iron and copper losses of two transformers at full load
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27. The purpose of performing Surnpner’s test is mainly to find out

(a) regulation of the transformer
(b) efficiency of the transformer
(c) the temperature rise on full load economically
(d) none of the above


Answer: (c) the temperature rise on full load economically
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28. When 240 V D.C. supply is given to an unloaded 220 V, 50Hz transformer

(a) secondary will, carry heavy current
(b) primary will carry heavy current and may possibly burn
(c) we will get A.C. voltage on secondary side according to turn ratio
(d) we will get high voltage on secondary side


Answer: (b) primary will carry heavy current and may possibly burn
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29. In a transformer, if the magnitude of magnetizing current is more

(a) its power factor will become low on leading side
(b) its power factor will become low on lagging side
(c) it has no effect on the power factor of the transformer
(d) none of the above


Answer: (b) its power factor will become low on lagging side
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