Core Type Transformer MCQ

1. The colour of fresh dielectric oil used in transformers is

(a) dark brown.
(b) pale-yellow.
(c) pale-pink.
(d) white-grey.

2. The transformer oil should have

(a) low volatility.
(b) high dielectric strength.
(c) good resistance to emulsion with water.
(d) low viscosity to provide good heat transfer.
(e) all of the above.

3. Transformer oil must be free from

(a) moisture.
(b) sludges.
(c) gases.
(d) sulphur.

4. The core and windings of a transformer are put in a steel tank in order to

(a) make it suitable for outdoor operation.
(b) provide protection against mechanical damages and provide additional cooling.
(c) improve its appearance.
(d) all of the above.

5. Conservator (for transformer) is used

(a) to take up the expansion of oil due to temperature rise.
(b) to act as an oil storage.
(c) for better cooling of transformer.
(d) None of the above. [A.M.I.E. Sec. B. Electrical Machines Summer 2004]

6. Consider the following statements relating to the constructional features of a large power transformer:

1. The conservator is used to maintain the level of oil in the transformer tank.
2. The bushing is used to protect transformer insulation against lightning voltages. 3. The Buchholz relay is an overcurrent relay.
3. Silica gel is used to absorb moisture.

Which of these statements are correct?
(a) 1, 2, 3 and 4.
(b) 2 and 3.
(c) 1 and 4.
(d) 1, 2 and 4. [U.P.S.C. I.E.S. 2003]

7. In a large power transformer, a “conservator” drum is provided above the completely oil filled transformer tank and connected to it by a short pipe. The conservator drum is linked to external air through a breather. What is the purpose of providing the conservator?

(a) To store reserve oil to make up oil losses due leakage.
(b) To prevent explosion due to rise in oil pressure inside the tank during a fault. (c) To accommodate change in oil-level during the “load -cycle” of the transformer load.
(d) To exert additional pressure by the conservator-oil on the oil inside the main tank to prevent disintegration of oil at high temperature. [U.P.S.C. I.E.S. E.E.-II, 2007]

8. Consider the following statements regarding transformers:

1. The function of the magnetizing component of no-load current is to sustain the alternating flux in the core.
2. Short-circuit test is performed to find core losses only.
3. The function of the breather in transformer is to arrest flow of moisture when outside air enters the transformer.

Which of the statements given above are correct?
(a) 1 and 2 only.
(b) 1 and 3 only.
(c) 2 and 3 only.
(d) 1, 2 and 3. [U.P.S.C. I.E.S. E.E.-II, 2007]

9. Sludge formation in transformer oil is due to which one of the following ?

(a) Ingress of dust particles and moisture in the oil.
(b) Appearance of small fragments of paper, varnish, cotton and other organic materials in the oil.
(c) Chemical reaction of transformer oil with the insulating materials.
(d) Oxidation of transformer oil. [U.P.S.C. I.E.S. E.E.-II, 2008]

10. In a power transformer, the breather is provided in order to

(a) filter transformer oil.
(b) prevent ingress of moisture with air.
(c) provide oxygen to the cooling oil.
(d) provide fresh air for increasing cooling effect.

11. The chemical used in breather of a transformer should have the quality of

(a) absorbing moisture.
(b) ionizing air.
(c) cleansing the transformer oil.
(d) none of the above.

12. Malfunctioning of the Buchholz relay may be caused due to

(a) heavy external short circuits.
(b) improper breather action.
(c) dropping of oil level below the relay level during operation.
(d) excessive overheating.

13. A Buchholz relay is used for

(a) protection of a transformer against all internal faults.
(b) protection of a transformer against external faults.
(c) protection of a transformer against both, internal and external faults.
(d) protection of induction motors. [U.P.S.C. I.E.S. E.E.-II, 206]

14. For system voltages exceeding 66 kV, condenser bushings are preferred over non-condenser bushings because

(a) the axial stresses can be eliminated.
(b) the radial stresses can be made independent of the radial thickness of the dielectric.
(c) optimum utilization of dielectric because of uniform potential distribution results in reduction of radial and axial dimensions of the bushings.
(d) none of the above.

15. Which is the arrangement of windings in a core type single phase transformer?

(a) Half lv inside and half hv outside on each core limb.
(b) lv on one core limb and hv on the other.
(c) Sandwiched lv and hv discs on each core limb.
(d) Half hv inside and half hv outside on each core limb. [A.M.I.E. Sec B. Winter 1994]

16. For core type power transformers, both primary and secondary windings have circular coil sections, as it

(a) reduces core material requirement and so also reduces the core loss.
(b) gives the strongest mechanical shape.
(c) is easier to wind.
(d) reduces the copper requirement.

17. With stepping in construction of transformer core

(a) copper losses are reduced.
(b) copper is saved.
(c) high flux density can be achieved.
(d) mechanical strength to the core is improved.
(e) both (a) and (b).

18. A shell type transformer is commonly used as it has

(a) two magnetic paths.
(b) reduced magnetic flux leakage.
(c) reduce copper losses.
(d) both (a) and (b).

19. Spiral core transformer, in which core is made up of steel strip has the advantage(s) of

(a) minimum losses.
(b) lighter construction.
(c) lesser weight.
(d) all of these.

20. Distribution transformers have core losses

(a) > copper loss.
(b) < copper losses.
(c) = copper loss.
(d) = copper losses ÷ 2.

21. Distribution transformers are designed to have maximum efficiency nearly at …….. of full load.

(a) 100%
(b) 70%
(c) 25%
(d) 10%

22. A distribution transformer is selected on the basis of

(a) voltage regulation.
(b) efficiency.
(c) all day efficiency.
(d) none of those.

23. The distribution transformers are designed with minimum possible iron losses. This is because

(a) the primary of a distribution transformer is energized for all the 24 hours.
(b) iron losses will cause undue heating.
(c) the iron losses may cause damage to the insulation.
(d) none of the above.

24. Which part of transformer is subjected to maximum heating ?

(a) Frame.
(b) Core.
(c) Winding
(d) Oil.

25. Which of the following methods is employed for cooling of power transformers of rating not exceeding 10 MVA ?

(a) Air blast cooling.
(b) Natural oil cooling.
(c) Forced oil cooling.
(d) Natural air cooling.

26. Natural air cooling is used for transformers of rating up to

(a) 100 kVA.
(b) 500 kVA.
(c) 5 – 10 kVA.
(d) 10 MVA.

27. Addition of tubes to the transformer tank improves heat dissipation capacity because of

(a) additional cooling surface.
(b) additional dissipation by radiation only.
(c) additional dissipation by convection only.
(d) additional dissipation by radiation and convection both. [A.M.I.E. Sec B. Summer 1993]

28. The winding used in a 3-phase shell type transformer is[/expander_maker] type.

(a) circular
(b) cylindrical
(c) sandwich
(d) rectangular

29. The low-voltage winding of a core type transformer is subdivided into two equal halves, each of half the original width of the single winding with the high-voltage winding in between (instead of having the usual construction of low voltage winding adjacent to the core and surrounded by the high-voltage winding). Such an interlacing of coils would make the combined primary and secondary leakage reactance (in terms of the primary) nearly

(a) twice.
(b) equal.
(c) half.
(d) one-fourth. [U.P.S.C. I.E.S. E.E.-II, 1997]

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