MCQ Questions on Transformer

1.A voltage transformer of which class of accuracy can be used for precision testing in standard laboratories?

(a) 0.1 class
(b) 10 class
(c) 5.00 class
(d) 1000 class

2. In a transformer the tappings are generally provided on

(a) primary side
(b) secondary side
(c) low voltage side
(d) high voltage side

3. The function of conservator in a transformer is

(a) to protect against internal fault
(b) to reduce copper as well as core losses
(c) cool the transformer oil
(d) take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings.

4.A Buchholz relay call be installed on

(a) auto-transformers
(b) air-cooled transformers
(c) welding transformers
(d) oil cooled transformers

5.Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds…………… degree Celsius.

(a) 50
(b) 80
(c) 100
(d) 150

6.The main reason for generation harmonics in a transformer could be

(a) fluctuating load
(b) poor insulation
(c) mechanicalvibrations
(d) saturation of core

7. Distribution transformers are generally designed for maximum efficiency around

(a) 90% load
(b) zero load
(c) 25% load
(d) 50% load

8.Star/star transformers work satisfactorily when

(a) load is unbalanced only
(b) load is balanced only
(c) on balanced as well as unbalanced loads
(d) none of the above.

9.Delta/star transformer works satisfactorily when

(a) load is balanced only
(b) load is unbalanced only
(c) on balanced as well as unbalanced load
(d) none of the above

10.Buchholz’s relay gives warning and protection against

(a) electrical fault inside the transformer itself
(b) electrical fault outside the transformer in outgoing feeder
(c) none of the above .

11.The magnetizing current of a transformer is usually small because it has

(a) small air gap
(b) large leakage flux
(c) laminated silicon steel core
(d) fewer rotating parts.

12.The path of the magnetic flux in transformer should have

(a) high reluctance
(b) low reactance
(c) high resistance
(d) low resistance

13.Noise level test in a transformer is a

(a) special test
(b) routine test
(c) type test
(d) none of the above.

14.Which of the following is not a routine test on transformers?

(a) Core insulation voltage test
(b) Impedance test
(c) Radio interference test
(d) Polarity test

15.A transformer can have zero voltage regulation at

(a) leading power factor
(b) lagging power factor
(c) unity power factor
(d) zero power factor

16.Helical coils can be used on

(a) low voltage side of high kVA transformers
(b) high frequency transformers
(c) high voltage side of small capacity transformers
(d) high voltage side of high kVA rating transformers.

17.Harmonics in transformer result in

(a) increased core losses
(b) increased I²R loss
(c) magnetic interference with communication circuits
(d) all of the above.

18.The core used in high frequency transformer is usually

(a) copper core
(b) cast-iron core
(c) air core
(d) mild-steel core.

19.The value of flux involved in the E.M.F. equation of a transformer is

(a) average value
(b) R.M.S.value
(c) maximum value
(d) instantaneous value.

20. Silicon steel used in laminations mainly reduces

(a) hysteresis loss
(b) eddy current losses
(c) copper looses
(d) all of the above.

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

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

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

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

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

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

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

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

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.

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

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