# TRANSFORMER PART TWO

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

1. Which of the following statements is/are correct statements?
1. For ideal transformer efficiency is 100%
2. both
3. For ideal transformer voltage regulation is 100%
4. none of these

2. Scott connections are used for
1. single phase to three phase transformation
2. three phase to two phase transformation
3. any of the above
4. three phase to single phase transformation

3. In which transformer, the tertiary winding is used?
1. Star – star
2. Delta – star
3. Delta – delta
4. Star – delta

4. For successful parallel operation of two single phase transformers, the most essential condition is that their
1. polarities are properly connected
2. percentage impedance are equal
3. turn- ratios are exactly equal
4. KVA ratings are equal

5. A delta/star transformer is connected in parallel to a star/delta transformer. The turn ratio former is x times latter, the x is
1. √3
2. 3
3. 1/3
4. 1/√3

6. Two transformers operating in parallel will share the load depending on their
1. per unit impedance
2. ratings
3. efficiency
4. leakage reactance

7. A 100/10, 50 VA double winding transformer is converted to 100/110 V auto transformer. The rating of auto transformer is
1. 550 VA
2. 100 VA
3. 110 VA
4. 500 VA

8. Tappings of a transformer are provided
1. at the middle of hv side
2. at the phase end of hv side
3. at the neutral side end of hv side
4. at the phase end of lv side

9. In an auto-transformer, power is transferred through
1. None of these
2. Both
3. Induction process only
4. Conduction process only

10. It is an advisable to use auto transformer if the transformation ratio is
1. 0.5
2. Greater than 1
3. 0.25
4. near to 1

11. In auto transformer if the turn ratio is K, What is the power transferred inductively
1. (1-K) × input power
2. none of these
3. both
4. K × input power

12. A 10KVA auto transformer, turn ratio is 0.4. Find the power transferred inductively?
1. 4 KVA
2. 10 KVA
3. 6 KVA
4. 0 KVA

13. A 20KVA auto transformer, turn ratio is 0.8. Find the power transferred conductively?
1. 4KVA
2. 16KVA
3. 20KVA
4. 0KVA

14. In an auto transformer, for what value of turn ratio, power transferred by inductively and conductively are same?
1. any of the
2. 0
3. 0.5
4. 1

15. The
total core loss of a 400 V, 50 Hz transformer is 2400W, when it is
supplied by 200 V, 25 Hz loss is 800W. Calculate eddy current loss and
hysteresis loss?

1. 1600W, 800W
2. 800W, 1600W
3. 1400W, 1000W
4. 1000W , 1400W

16. In a transformer which of the following losses are zero ?
1. rotational loss
2. iron loss
3. copper loss
4. all of these

17. When maximum flux density is constant, the eddy current losses are proportional to
1. V
2. f

18. When flux density is constant in a transformer, hysteresis loss varies as
1. f
2. V

19. In a transformer maximum flux density is not constant, the eddy current loss varies as
1. f
2. V

20. The working principle of transformer depends on
1. Coulombs law.
2. Amperes law.
3. Newtons law.
4. Faradays law of electromagnetic induction.

21. Addition of 0.3 % to 4.5 % silicon to iron
1. increases the hysteresis loss.
2. increases the electrical resistivity of iron.
3. reduces the saturation magnetization.
4. none of these

22. A laminated iron core has reduced eddy current losses because
1. more wire can be used with less dc resistance in coil.
2. the magnetic flux is concentrated i
3. the lamination are insulated from each other.
4. the lamination are stacked vertically.

23. The two windings of a transformer have an inductor of 2 H each. If mutual inductor between them is also 2 H, then
1. none of these.
2. transformer is an ideal transformer.
3. it is a perfect transformer.
4. turns ratio of the transformer is also two.

24. Lamination of core are generally made of
1. silicon steel.
2. stainless steel.
3. case iron.
4. carbon.

25. A single-phase transformer has its maximum efficiency at 60 percent of full load. At full load copper loss will be
1. more than core loss.
2. equal to core loss.
3. zero.
4. less than core loss.

26. In a core type transformer
1. LV winding is placed nearer to the core limb.
2. HV and LV windings are placed in different core limbs.
3. HV winding is placed nearer to the core limb.
4. any of the LV or HV can be placed nearer to the core limb.

27. The primary and secondary windings of a transformer are

28. At what power factor, the voltage regulation of a transformer can be zero ?
1. Lagging power factor
2. Zero power factor.
3. Unity power factor.
4. Leading power factor.

29. In a three phase star – delta transformer, what is the angle difference between primary and secondary phase voltages?
1. Delta side lags by -30°.
2. Delta side leads by 30°.
3. Star side leads by 30°.
4. Star side lags by -30°.

30. What will be the eddy current loss if the supply frequency of a transformer becomes double?
1. Remains same.
2. Doubled.
3. Four times.
4. Eight times.

31. The efficiency of a transformer is mainly dependent on
1. dielectric losses.
2. stray losses.
3. copper losses.
4. core losses.

32. Transformers operating in parallel will share the load depending upon their
1. efficiency.
2. leakage reactance.
3. rating.
4. percentage impedance

33. No load primary current in a transformer
1. lags behind applied voltage somewhat less than 90Ã
2. lags behind applied voltage by exactly 90Ã
3. leads the applied voltage somewhat less than 90Ã
4. leads the applied voltage by exactly 90Ã

34. Which of the following is minimized by laminating the core of a transformer?
1. Eddy current loss.
2. Hysteresis loss.
3. Copper loss.
4. Stray loss.

35. Breather is provided in a transformer to
1. absorb moisture of air during breathing.
2. filter the transformer oil.
3. absorb moisture from air entering in transformer.
4. provide cold air in transformer.

36. ron loss in a transformer mainly occurs in
1. transformer insulating oil.
2. steel core in transformer.
3. winding of transformer.
4. iron made tank of transformer.

37. Short
circuit test is performed on a transformer with a certain impressed
voltage at rated frequency. If the short circuit test is now performed
with the same magnitude of impressed voltage, but at frequency higher
than the rated frequency then

1. The magnetude of current will increase, but power factor will decrease.
2. The magnitude of current will decrease but the power factor will increase.
3. The magnitude will both increase.
4. The magnitude of circuit as well as the power factor will decrease.

38. In a transformer the magnetic coupling between the primary and secondary winding can be increased by
1. increasing the number of turns.
2. using soft material for winding.
3. using the magnetic core of low reluctance.
4. using transformer oil of better quality.

39. The short circuit test on a transformer is conducted to obtain
1. hysteresis loss.
2. eddy current loss.
3. copper losses.
4. core loses only.

40. An
auto transformer having a transformation ratio of 0.8 supplies a load
pf 10 KW. The power transfered inductively from the primary to secondary
is

1. 8 KW.
2. 10 KW.
3. 2 KW.
4. 0 KW

41. In one 132 / 33 kV transformer the LV resistance is 0.02 per unit. The resistance referred to HV side is
1. 0.02 pu.
2. 0.01 pu.
3. 0.08 pu.
4. 0.16 pu.

42. Air core transformer as compared to iron core transformer, has
1. less magnetic core loss.
2. more magnetic core loss.
3. no magnetic core loss.
4. more copper loss.

43. CRGO steel is used in the core of transformer to reduce
1. both eddy current and hysteresis loss.
2. hysteresis loss.
3. eddy current loss.
4. ohmic loss.

44. If input of a transformer is square wave the output will be
1. pulsed wave.
2. square wave.
3. triangular wave.
4. sine wave.

45. Two
transformers with identical rating, are designed with flux densities of
1.2 and 1.4 Wb / m sqr respectively. The weight of first transformer
per kVA is

1. none of these.
2. more than that of second transformer.
3. equal to that of second transformer.
4. less than that of second transformer.

46. The flux involved in the emf equation of a transformer has
1. rms value.
2. average value.
3. total value.
4. maximum value.

47. The no load current in a transformer lags the applied voltage by
3. 90°.
4. 0°.

48. The leakage flux in a transformer depends upon
1. the mutual flux.
2. the frequency.
3. the load current.
4. the applied voltage.

49. Which of the following transformer insulating oil generally used in India?
1. Aromatics based insulating oil.
2. Naphtha based insulating oil.
3. Paraffin based insulating oil.
4. Olefin based insulating oil.

50. Winding conductors of an electrical power transformer are mainly insulated by
1. paper insulation.
2. wooden insulation.
3. rubber insulation.
4. cotton insulation.