ONLINE MCQ EE-TRANSFORMER PART THREE

TRANSFORMER PART THREE

Instructions: Click the answer button to see the correct answer.

  1. A step up transformer increases
    1. current.
    2. voltage.
    3. power.
    4. frequency.

    Answerb

  2. In a step down transformer which one of the following statements is true?
    1. Secondary current is less than primary current.
    2. Secondary power is less than primary power.
    3. Number of secondary turns is less than primary turns.
    4. Number of secondary turns is more than that of primary.

    Answerc

  3. When a transformer is loaded, the secondary terminal voltage drops. That means power factor is
    1. lagging.
    2. unity.
    3. leading.
    4. zero.

    Answera

  4. If
    Ke is eddy current constant, Kf is form factor, f is supply frequency,
    Bm maximum flux density in core of transformer, the expression of eddy
    current loss in transformer, is given by
    1. Kef²Kf²Bm.
    2. Kef²Kf²Bm²
    3. Kef²KfBm².
    4. KefKf²Bm².

    Answerb

  5. Stray losses in transformer occurs in
    1. paper insulation in transformers.
    2. winding conductors and steel structures of transformer.
    3. transformer insulating oil.
    4. steel core.

    Answerb

  6. If
    iron loss and full load copper loss of any transformer are denoted by
    Pi and Pc, then the load corresponding to maximum efficiency is given by
    1. (Pi / Pc)³. full Load
    2. (Pi / Pc)².full Load.
    3. √(Pi / Pc).Full Load.
    4. (Pi / Pc).full Load.

    Answerc

  7. Secondary winding of an auto transformer is also called
    1. compensating winding.
    2. damping winding.
    3. common winding.
    4. tertiary winding.

    Answerc

  8. Tertiary winding in a transformer is mostly
    1. zig – zag star connected.
    2. zig – zag delta connected.
    3. delta connected.
    4. star connected.

    Answerc

  9. The main purpose of providing tertiary winding in a three phase transformer is
    1. to suppress harmonic and unbalance in voltage.
    2. to carry extra load.
    3. to interconnect three voltage systems.
    4. none of these

    Answera

  10. When operating, two or more transformers in parallel, % impedance of these transformers should be
    1. inversely proportional to MVA rating of transformers.
    2. proportionate to MVA rating of transformers.
    3. such that actual impedance of all transformers would be same.
    4. same.

    Answerd

  11. Tap changer is generally provided in
    1. power transformer.
    2. earthing transformer.
    3. current transformer.
    4. voltage transformer.

    Answera

  12. The heat generated in the transformer is dissipated mainly by
    1. all of these
    2. conduction.
    3. convection.
    4. radiation.

    Answerc

  13. Transformer cooling and insulating oil must be of
    1. low viscosity.
    2. low BDV.
    3. low resistivity.
    4. high viscosity.

    Answera

  14. Normally for the design of transformer the ambient temperature is taken as
    1. 32°C.
    2. 35°C.
    3. 27°C.
    4. 45°C.

    Answerd

  15. Which of the following machine will have maximum efficiency?
    1. Induction motor.
    2. Electrical power generator.
    3. DC motor.
    4. Electrical power transformer.

    Answerd

  16. The heat transfer by convection in a transformer least depends on
    1. surface area.
    2. temperature difference.
    3. color of the paint.
    4. air velocity.

    Answerc

  17. Which of the following is not a part of transformer?
    1. Tap changer.
    2. Radiator.
    3. Commutator.
    4. Conservator tank.

    Answerc

  18. Maximum allowable acidity level of power transformer insulating oil is generally taken as
    1. 1 mg of KOH / gm.
    2. 2 mg of KOH / gm.
    3. 0.3 mg of KOH / gm.
    4. 0.5 mg of KOH / gm.

    Answerc

  19. Maximum allowable tan – delta (tanδ) of dielectric dispassion factor of power transformer insulating oil is generally taken as
    1. 3 at 90°C.
    2. 1 at 90°C.
    3. 0.5 at 90°C.
    4. 2 at 90°C.

    Answerb

  20. Minimum allowable resistivity of power transformer insulating oil is generally taken as
    1. 3 X 10^12 Ω – cm at 27°C and 0.3 X 10^12
    2. 2 X 10^12 Ω – cm at 27°C and 0.2 X 10^12
    3. 4 X 10^12 Ω – cm at 27°C and 0.4 X 10^12
    4. 1 X 10^12 Ω – cm at 27°C and 0.1 X 10^12

    Answerd

  21. Maximum allowable moisture content of power transformer insulating oil is generally taken as
    1. 25 ppm.
    2. 20 ppm.
    3. 35 ppm.
    4. 45 ppm.

    Answerc

  22. What does the use the of height flux density value in transformer design lead to?
    1. Reduced copper loss.
    2. Reduced iron loss.
    3. Increase in weight/KVA.
    4. Decrease in weight/KVA.

    Answerd

  23. Dissolve gas analysis of transformer oil is carried out to determine
    1. condition of bushing stud.
    2. condition of bushings.
    3. condition of transformer.
    4. condition of transformer oil.

    Answerc

  24. Fufuraldehyde analysis is done to determine the
    1. condition of lamination on CRGO steel sheet.
    2. condition of oil in transformer.
    3. condition of cork gaskets used in transformer
    4. condition of paper insulation in transformer.

    Answerd

  25. A
    10 Ω load is connected to the secondary of a single phase 3300/110 V
    power transformer. The effective load on the 3.3kV bus bar is nearly
    1. 300 kΩ
    2. 10 kΩ
    3. 9 kΩ
    4. 0.9 kΩ

    Answerc

  26. Cross-section of the iron core of a power transformer is approximately circular. This is done because`
    1. it is easy to prepare circular coils
    2. it is easy to assemble circular iron core
    3. all of these
    4. electromagnetic forces tend to make the coil circular

    Answerc

  27. If copper loss of a transformer at 1/4 th of full load is 100 W, then its full load copper loss would be
    1. 800 W
    2. 400 W
    3. 1600 W
    4. 100 W

    Answerc

  28. Sumpner’s test is carried out
    1. Due to none of the above reasons
    2. mainly to find out regulation of the transformer.
    3. mainly to find out the temperature rise on full load economically.
    4. mainly to find efficiency of the transformer.

    Answerc

  29. A
    2000/200 V, 50 Hz single-phase transformer has an exciting current of
    0.5A and a core loss of 600W. When H.V. side is energized by the rated
    voltage and frequency, the magnetizing current is
    1. 0.2 A
    2. 0.4 A
    3. 0.3 A
    4. 0.1 A

    Answerc

  30. A 250 kVA, 11000/400 V and 50 Hz single-phase transformer has 80 turns on the secondary, what is the maximum value of flux?
    1. 0.2 mWb
    2. 2475 mWb
    3. 55.2 mWb
    4. 22.5 mWb

    Answerd

  31. In
    a normal operation of 400V, 50 Hz transformer, the total iron loss is
    2500W. When the supply voltage and frequency are reduced to 200V and 25
    Hz respectively, the corresponding loss is 850W. The eddy-current loss
    at normal voltage and frequency is
    1. 200
    2. 800 W
    3. 400 W
    4. 1600 W

    Answerd

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ONLINE MCQ EE AND ECE-POWER ELECTRONICS PART ONE
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