50 Important Multiple choice Question Of Transformer – 2021 II Electrical most asked MCQ
(A) 100 KVA
(B) 500 KVA
(C) 5-10 KVA
(D) 10 MVA
Ans: (C) 5-10 KVA
2. Which of the following methods is employed for cooling of power transformers of rating not exceeding 10MVA?
(A) Air Blast cooling
(B) Natural oil cooling
(C) Forced oil cooling
(D) Natural air cooling
Ans: (B) Natural oil cooling
3. Which part of the transformer is subjected to maximum heating?
(A) Frame
(B) Core
(C) Winding
(D) oil
Ans: (C) Winding
4. The distribution transformers are designed with minimum possible iron losses. this is because
(A) The primary of a distribution transformer is energized for all 24 hours.
(B) Iron losses will cause undue heating
(C) The iron losses may cause damage to the insulation
(D) None of the above
Ans: (A) The primary of a distribution transformer is energized for all 24 hours.
5. A distribution transformer is selected on the basis of
(A) Voltage regulation
(B) efficiency
(C) all day efficiency
(D) none of those
Ans: (C) all day efficiency
6. Distribution transformer are designed to have maximum efficiency nearly at ....... of full load.
(A) 100 %
(B) 70 %
(C) 25 %
(D) 10 %
Ans: (B) 70 %
7. Distribution transformer have core losses
(A) > copper loss
(B) < copper losses
(C) = copper loss
(D) = 1/2(copper losses)
Ans: (B) < copper losses
8. 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
Ans: (D) all of these
9. A shell-type transformer is commonly used as it has
(A) Two magnetic paths
(B) Reduced magnetic flux leakage
(C) reduced copper losses
(D) Both (A) and (B)
Ans:(D) Both (A) and (B)
10. With stepping in construction of transformer core
(A) copper losses are reduced
(B) copper is saved
(C) high flux density can be achieved
(D) mechaniacal strength to the core is improved
(E) both (A) and (B)
Ans: (E) both (A) and (B)
11. For core type power transformers, both primary and secondary winding 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) reduce the copper requirement.
Ans: (B) gives the strongest mechanical shape
12. 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 half hv outside on each core limb
Ans: (A) Half lv inside and half hv outside on each core limb
13. For system voltages exceeding 66Kv, condenser bushing are prefered over non-condeser bushing because
(A) 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 a reduction of radial and axial dimensions of the bushings.
(D) None of the above.
Ans: (C) optimum utilization of dielectric because of uniform potential distribution results in a reduction of radial and axial dimensions of the bushings.
14. A Buchholz relay is used for
(A) Protection of transformer against all internal faults.
(B) protection of a transformer against external faults.
(C) Protection of a transformer against both internal and external fault
(D) protection of induction motors.
Ans:(A) Protection of transformer against all internal faults.
15. Which of the following statements associated with Buchholz relay is not TRUE?
(A) it is a voltage-sensitive device
(B) It is used only on oil-cooled transformers.
(C) It is usually not provided on the transformer of ratting below 500KVA.
(D) Its operating time is of the order of 0.1 seconds.
Ans: C) It is usually not provided on the transformer of ratting below 500KVA.
16. Malfunctions of the Bucholz relay may be caused due to
(A) Heavy external short circuit
(B) improper breather action
(C) Dropping of oil level below the relay level during operation
(D) Excessive overheating
Ans: (C) Dropping of oil level below the relay level during operation
17. The chemical used in the 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
Ans: (A) Absorbing moisture
18. 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 increased cooling effect
Ans: (B) Prevent ingress of moisture with air
19. Sludge formation in transformer oil is due to which one of the following?
(A) Ingress of dust particle 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
Ans: (D) Oxidation of transformer oil
20. Conservator( for a 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
Ans: (A) to take up the expansion of oil due to temperature rise
21. Which of the following is minimized by laminating the core of a transformer?
(A) Hysteresis loss
(B) Eddy current loss
(C) Heat loss
(D) All of the above
Ans: (B) Eddy current loss
22. The function of the breather in a transformer is
(A) To provide oxygen to the cooling oil
(B) To provide cooling air
(C) To arrest flow of moisture when outside air enters the transformer
(D) To filter the transformer oil
Ans: (C) To arrest flow of moisture when outside air enters the transformer
23. Iron loss in a transformer occurs in
(A) Core
(B) Winding
(C) Insulating Oil
(D) Main body
Ans: (A) Core
24. Under No-load conditions, which of the following loss is negligible?
(A) Hysteresis loss
(B) Eddy current loss
(C) Copper loss
(D) All losses have same magnitude
Ans: (C) Copper loss
25. Open circuit test of transformer gives
(A) Hysteresis loss
(B) eddy current loss
(C) Sum of hysteresis loss and eddy current loss
(D) copper loss
Ans: (C) Sum of hysteresis loss and eddy current loss
26. Copper loss in transformer occurs in
(A) Core
(B) Winding
(C) main body
(D) Bushings
Ans: B) Winding
27. 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
Ans: (B) Provide protection against mechanical damages and provide additional cooling.
28. Transformer Oil must be free from
(A) Moisture
(B) Sludges
(C) gases
(D) Sulfur
Ans: (A) Moisture
29. The transformer oil should have
(A) low volatility
(B) high dielectric strength
(C) good resistance to the emulsion with water
(D) low viscosity to provide good heat transfer
(E) all of above
Ans: (E) all of above
30. The color of fresh dielectric oil used in transformers is
(A) Dark brown
(B) Pale yellow
(C) pale pink
(D) white grey
Ans: (B) Pale yellow
31. The function of oil in a transformer is
(A) to provide insulation and cooling
(B) To provide protection against lightning
(C) To provide protection against short circuits.
(D) To provide lubrication.
Ans:(A) to provide insulation and cooling
32. In a transformer, insulating materials may be fail due to
(A) moisture
(B) Dust
(C) Voids in the winding
(D) anyone or more of the above
Ans: (D) any one or more of the above
33. Minor insulation in a transformer is the insulation between the
(A) LV winding and core
(B) LV and HV windings
(C) turns of the winding
(D) layers of the winding
(E) both (C) and (D)
Ans: (E) both (C) and (D)
34. Major insulation in a transformer is the insulation between the
(A) LV winding and core
(B) LV winding and Hv winding
(C) turns of the winding
(D) Both (A) and (B)
Ans: (D) Both (A) and (B)
35. When the transformer winding suffers a short circuit, the adjoining turns of the same winding experience
(A) an attractive force
(B) A repulsive force
(C) no force
Ans: (A) an attractive force
36. In transformers, primary and secondary are interlaced so that
(A) there may be maximum flux leakage between the two windings
(B) copper is saved
(C) both (A) and (B)
(D) statement is false
Ans: (A) there may be maximum flux leakage between the two windings
37. In power transformer
(A) the primary winding is always wound with many turns of the thin wire
(B) the secondary winding is always wound with a lesser number of turns of thin wire
(C) low voltage winding is always wound with lesser number of turns of thicker wire
(D) high voltage winding is always wound with larger number of turns of thicker wire.
Ans: (C) low voltage winding is always wound with lesser number of turns of thicker wire
38. Low voltage windings are always placed next to the core in the case of concentric windings as in this case ........is/are reduced.
(A) hysteresis loss
(B) leakage flux
(C) eddy current loss
(D) copper loss
(E) insulation requirement
Ans: (E) insulation requirement
39. The concentric windings are used in core type transformers with .......winding placed next to the core.
(A) LV
(B) HV
(C) primary
(D) secondary
Ans: (A) LV
40. The leakage flux of primary and secondary winding can be reduced to the minimum by
(A) winding primary and secondary coils on the separate limbs.
(B) Winding primary and secondary coils one upon the other coaxially
(C) increasing the number of turns
(D) employing low permeability magnetic material core
Ans: (B) Winding primary and secondary coils one upon the other coaxially
41. The primary and secondary windings are interlaced for
(A) easiness of coil making
(B) reduced leakage reactance
(C) reduced cost
(D) uniform heating
Ans: (B) reduced leakage reactance
42. The noise in the transformer, caused by vibrations of laminations set by magnetic force, is termed as
(A) zoom
(B) hum
(C) buzz
(D) none of these
Ans: (B) hum
43. The degree of mechanical vibrations caused by core laminations in a transformer depends on
(A) size of laminations
(B) gauge of laminations
(C) tightness of clamping
(D) all of the above
Ans: (D) all of the above
44. For CRGOS mitred overlap is prefered for the core yoke joints as it
(A) reduce the magnetising current and also the core losses
(B) improve the mechanical strength
(C) reduce the magnetostriction
(D) make better use of core space.
Ans: (A) reduce the magnetising current and also the core losses
45. The joints in the transformer core laminations are staggered so as to
(A) avoid continuous gap causing the increase in magnetising current
(B) Increase the mechanical strength of the assembled core
(C) avoid undue humming noise
(D) facilitate assembly of core after putting preformed coils on the core
(E) all of the above
Ans: (D) facilitate assembly of core after putting preformed coils on the core
46. Cores of large power transformers are made from which one of the following
(A) hot rolled steel
(B) cold rolled non gain oriented steel
(C) cold rolled grain oriented steel
(D) ferrite
Ans: (C) cold rolled grain oriented steel
47. The size of the transformer core depends upon
(A) frequency
(B) permissible flux density in the core material
(C) are of the core
(D) both (A) and (B)
Ans: (D) both (A) and (B)
48. ferrite cores are employed in high-frequency transformers due to their
(A) Low resistance
(B) High resistance
(C) low permeability
(D) high hysteresis loss
Ans:(B) High resistance
49. The inductive reactance in the transformer depends on
(A) electromotive force
(B) magnetomotive force
(C) magnetic flux
(D) leakage flux
Ans: (D) leakage flux
50. The flux in the transformer core
(A) increase with load
(B) decrease with load
(C) remain constant irrespective of load
(D) none of the above
Ans: (C) remain constant irrespective of load
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