Transformers

31. If a transformer is switched on to a voltage more than the rated voltage

  1. its power factor will deteriorate
  2. its power factor will increase
  3. its power factor will remain unaffected
  4. its power factor will be zero

Correct answer: (A)
its power factor will deteriorate

32. If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be

  1. R2/VK
  2. R2IK2
  3. R22!K2
  4. R22/K

Correct answer: (B)
R2IK2

33. If the percentage impedances of the two transformers working in parallel are different, then

  1. transformers will be overheated
  2. power factors of both the transformers will be same
  3. parallel operation will be not possible
  4. parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load

Correct answer: (D)
parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load

34. If the supply frequency to the transformer is increased,”the iron loss will

  1. not change
  2. decrease
  3. increase
  4. any of the above

Correct answer: (C)
increase

35. In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are

  1. hysteresis and eddy current losses
  2. friction and windage losses
  3. copper losses
  4. none of the above

Correct answer: (A)
hysteresis and eddy current losses

36. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are

  1. friction and windage losses
  2. copper losses
  3. hysteresis and eddy current losses
  4. none of the above

Correct answer: (C)
hysteresis and eddy current losses

37. In a power or distribution transformer about 10 per cent end turns are heavily insulated

  1. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
  2. to absorb the line surge voltage and save the winding of transformer from damage
  3. to reflect the line surge and save the winding of a transformer from damage
  4. none of the above

Correct answer: (A)
to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

38. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of

  1. less than 15 A
  2. more than 15 A
  3. 15 A
  4. none of the above

Correct answer: (A)
less than 15 A

39. In a transformer routine efficiency depends upon

  1. supply frequency
  2. load current
  3. power factor of load
  4. both (b) and (c)

Correct answer: (D)
both (b) and (c)

40. In a transformer the energy is conveyed from primary to secondary

  1. through cooling coil
  2. through air
  3. by the flux
  4. none of the above

Correct answer: (C)
by the flux

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