Objective Type Questions on Transformer

1. Reduction in core losses and increase in permeability are obtained with transformer employing

(a) core built-up of laminations of cold rolled grain oriented steel
(b) core built-up of laminations of hot rolled sheet
(c) either of the above
(d) none of the above


Answer: (a) core built-up of laminations of cold rolled grain oriented steel
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2.In a power or distribution transformer about 10 pm cent end turns are heavily insulated

(a) to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
(b) to absorb the line surge voltage and save the winding of transformer from damage
(c) to reflect the line surge and save the winding of a transformer from damage
(d) 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
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3.Which of the following transformers is smallest ?

(a) 2 kVA 500 Hz
(b) 2 kVA 400 Hz
(c) 2 kVA 200 Hz
(d) 2kVA 50 Hz


Answer: (a) 2 kVA 500 Hz
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4.The purpose of a breather in a transformer is to provide cooling to the winding

(a) take insulting oil from the conservator
(b) provide insulation to the winding
(c) extract moisture from the air


Answer:(c) extract moisture from the air
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5.Cross-over windings are used for

(a) high voltage winding of large rating transformers
(b) high voltage winding of small rating transformers
(c) low voltage winding of small rating transformers
(d) none of these.


Answer: (b) high voltage winding of small rating transformers
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6.In core type transformers, the concentric windings are used with

(a) low voltage winding placed next to core
(b) low voltage winding on the outer-side
(c) high voltage winding placed next to core
(d) high voltage winding on the outer-side


Answer: (a) low voltage winding placed next to core
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7.The yoke sections of transformers using hot-rolled laminations is made 15 percentage greater than that of the core to

(a) to increase the size of the transformer
(b) to reduce the copper loss
(c) to reduce the iron loss in yoke and magnetizing current
(d) to provide better cooling.


Answer: (c) to reduce the iron loss in yoke and magnetizing current
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8.When two single phase transformers are running in parallel and if the impedance triangles of the transformers are not identical in shape and size then

(a) power factor of one transformer and power factor of common load will be same.
(b) power factors at which the transformers operate will be different from one another and again these will be different from power factor of common load.
(c) power factors at which the transformers operate will be same but different from power factor of common load.
(d) power factors at which the transformers operate and power factor of common load all will be same.


Answer: (b) power factors at which the transformers operate will be different from one another and again these will be different from power factor of common load.
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9.What is the typical use of an auto-transformer ?

(a) Control transformer
(b) Isolating transformer
(c) Variable transformer
(d) Toy transformer


Answer: (c) Variable transformer
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10. In a transformer the magnitude of mutual flux

(a) varies at low loads and constant at high loads
(b) is low at low loads and high at high loads
(c) is high at low loads and low at high loads
(d) same at all loads


Answer: (d) same at all loads
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11.The principle of working of a transformer is

(a) mutual induction
(b) static induction
(c) self induction
(d) dynamic induction.


Answer: (a) mutual induction
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12.In a transformer an insulating material may fail due to

(a) moisture
(b) dust
(c) voids in the winding
(d) any of the above


Answer: (d) any of the above
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13.The reactance of a transformer depends on

(a) leakage flux
(b) size of the core
(c) size of the tank
(d) all of the above.


Answer: (a) leakage flux
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14.In a transformer on no load, the input voltage

(a) is always at 60 degrees to the magnetizing current
(b) is in phase with magnetizing current
(c) leads the magnetizing current by 90 degrees
(d) lags the magnetizing by 90 degrees.


Answer: (c) leads the magnetizing current by 90 degrees
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15.The value of useful flux least depends on

(a) load
(b) magneto-motive force
(c) voltage
(d) all of the above


Answer: (a) load
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16.The type of load for which the voltage regulation of a transformer is negative is

(a) capacitive
(b) inductive
(c) resistive


Answer: (a) capacitive
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17.The magnetizing current for sinusoidal voltage applied, will be

(a) always sinusoidal
(b) always non-sinusoidal
(c) sinusoidal or non-sinusoidal depending upon the saturation point
(d) none of the above


Answer: (c) sinusoidal or non-sinusoidal depending upon the saturation point.
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18.The transformation ratio of a transformer, for a given application

(a) depends on secondary load
(b) is constant but not fixed
(c) is fixed but not constant
(d) none of the above


Answer: (c) is fixed but not constant
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19.The output current corresponding to the maximum efficiency for a transformer having core loss of 200 W and equivalent resistance referred secondary of 0.5 ohms is

(a) 5 A
(b) 10 A
(c) 15A
(d) 20 A


Answer: (d) 20 A
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20. The saving in copper achieved by converting two winding transformer into an auto-transformer is determined by

(a) load on the secondary
(b) voltage transformation ratio
(c) size of the transformer core
(d) magnetic quality of core material


Answer: (b) voltage transformation ratio
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21.While performing a short-circuit test on a transformer, usually low-voltage side is short-circuited because it has

(a) low insulation
(b) easy access
(c) lower terminal voltage and higher current rating
(d) more number of turns


Answer: (c) lower terminal voltage and higher current rating
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22. The secondary winding of a current transformer whose primary Is carrying current should

(a) not be open-circuited
(b) not be short-circuited
(c) either of the above
(d) none of the above


Answer: (a) not be open-circuited
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23.In large transformers, oil is invariably used in order to

(a) lubricate the core
(b) insulate the core
(c) insulate the coils
(d) none of the above


Answer: (c) insulate the coils
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24.Dust should never be allowed to accumulate on the windings and core of a dry type transformer because it

(a) reduces dissipation of heat
(b) may short-circuit the windings
(c) absorbs oil and grease
(d) tends to corrode the metal surface


Answer: (a) reduces dissipation of heat
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25.Increase in secondary current of a transformer brings about increase in primary current. This is possible because

(a) primary and secondary windings are capacitively coupled
(b) primary and secondary windings are inductively coupled
(c) primary and secondary windings are conductively coupled
(d) none of the above


Answer: (b) primary and secondary windings are inductively coupled
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26.An auto-transformer is preferred to a conventional 2-winding transformer

(a) where ratio of transformation is low
(b) where it is required to isolate the two windings electrically
(c) because it is much safer to use en auto-transformer
(d) where large number of secondary taps are needed


Answer: (a) where ratio of transformation is low
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27.Transformer for constant voltage applications is considered good if its voltage regulation is

(a) low
(b) high
(c) zero
(d) none of the above


Answer: (a) low
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28. Transformer supplying load having negative resistance characteristics such as arc load, is considered if its voltage regulation is

(a) low
(b) high
(c) either of the above
(d) none of the above


Answer: (b) high
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29.For given effective applied voltage of constant frequency eddy current losses

(a) become less with peaked wave shape of applied voltage
(b) independent of the wave shape of the applied voltage
(c) either of the above
(d) none of the above.


Answer: (b) independent of the wave shape of the applied voltage
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30.While rising and while falling, if a wave is symmetrical, it contains

(a) even harmonica in addition to fundamental
(b) odd harmonics in addition to fundamental
(c) both odd and even harmonics in addition to fundamental
(d) none of the above


Answer: (b) odd harmonics in addition to fundamental
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Objective Type Questions on Transformer

 

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