TRANSFORMER

LIST OF OBJECTIVES

 1.  Which of the following doesn't  change in transformer?

  Current                                          Voltage

  Frequency                                        All
Ans: Frequency

2. In a transformer, the energy is conveyed from primary to secondary through

  Cooling oil                                      air

  Flux                                                none
  Ans: Flux

3. A transformer core is laminated to

  Reduce hysteresis loss                   reduce eddy current loss

  Reduce copper loss                        all
  Ans: reduce eddy current loss

4. The degree of mechanical vibrations produced by the lamination of the transformer depends on

 Tightness of clamping                     gauge of lamination

 Size of lamination                          all
 Ans: all

5. The no-load current drawn by transformer is

  0.2 to 5%                                          2 to 5%

  12 to 15%                                         20 to 30%
  Ans: 2 to 5%

6. The path of a magnetic flux in a transformer should have

  High resistance                                High reluctance

  Low resistance                                Low reluctance
  Ans: Low reluctance

7. No load on a transformer is carried out to determine

  Copper loss                                      magnetizing current

  Magnetizing current and loss       efficiency of transformer
  Ans: Magnetizing current and loss 

8. The dielectric strength of transformer is expected to be

  11kV                                                  33kV

  66kV                                                  132kV
  Ans: 33kV

9. Sumpner’s test is conducted on transformer to determine

  Temperature                                   Stray loss

  All day efficiency                            None
  Ans: Temperature

10. The permissible flux density in case of cold rolled grain oriented  steel is around

 1.7Wb/m²                                         2.7Wb/m²      

 3.7Wb/m²                                               4.7Wb/m^{2         
  Ans: 2.7}Wb/m²      

11. The efficiency of the transformer will be maximum when

 Iron loss is greater than copper loss

  Iron loss is less than copper loss

  Iron loss =Copper loss

 None   
Ans: Iron loss =Copper loss             

12. No load current in the transformer

 Lags behind the voltage by about 75%

 Lead the voltage by about 75%

 Lags behind the voltage by about 15%

 Lead the voltage by about 15%
Ans: Lags behind the voltage by about 75%

13. The purpose of providing an iron core in a transformer is to

  Provide support to windings

 Decrease the reluctance of magnetic path

 Reduce hysteresis loss

 Reduce Eddy current loss
Ans: Decrease the reluctance of magnetic path

14. Which of the following isn’t the part of transformer installation?

 Conservator                                     Breather

 Buchholz relay                                 Exciter
Ans: Exciter

15. While conducting short circuit test on a transformer, the following side is short circuited

 HV side                                              LV side

 Primary                                             Secondary
Ans: LV side

16. In a transformer, following winding has got more cross sectional area

 LV winding                                        HV winding

 Primary                                             Secondary
Ans: LV winding

17. A transformer transforms

 Voltage                                              Current

 Power                                               Frequency
Ans: Power

18. Which winding in the transformer has more number of turns

 HV                                                      LV

 Primary                                             Secondary
Ans: HV

19. Efficiency of a power transformer is of the order of

 100%                                                 98%

 50%                                                   40%
Ans: 98%

20. A common method of cooling of power transformer is

 Natural air cooling                                          Oil Cooling

 Air blast cooling                                              any of the above
Ans: Oil Cooling

21. In a power transformer, routine efficiency depends upon

 Supply Frequency                                           Load

 Pf                                                                     both load and pf
Ans: Both load ans pf

22. In the transformer, the function of a conservator is to – protect the transformer from the damage when oil expands due to heating
23. Natural oil cooling is used for transformers upto rating- 3000kVA
24. Power transformers are designed to have maximum efficiency at

 Nearly full load                                50% full load

 70% full load                                    No load
Ans: Nearly full load

25. Transformer breaths in when

 Load on it increases                                       Load remains constant

 Load on it decreases                                      none
Ans: Load on it decreases

26. The maximum efficiency of a distribution transformer is at – 50%

27.  No load current of a transformer has- small magnitude and low pf

28.  Spacers are provided between adjacent coils- to provide free passage to the cooling oil

29.  Greater the secondary leakage flux- less will be the secondary induced emf

30.  The purpose of providing iron core in a step up transformer is- to decrease the magnitude of magnetizing current

31.  The power transformer is a constant

Main flux device                                               voltage device

Current device                                                  Power device
Ans: Main Flux device

32. Two transformers operating in parallel will share the load depending upon their

 Leakage reactance                                         pu impedence

 Efficiencies                                                       ratings
Ans: pu impedence

33. What will happen if the transformers working in parallel are connected with regard to polarity? - Incorrect polarity will result in dead short circuit

34. If the percentage impedance of the two transformers working in parallel are different then, - parallel operation will still be possible but the pf at which the two transformers operating will be different from the pf of the common load

35. In a transformer, the tapping are generally provided on- LV side

36. The use of higher flux density in the transformer design

      reduces weight/kVA                                             reduces Cu losses

      reduces iron loss                                                   increases part load efficiency

     Ans: reduces weight/kVA

37. The chemical used in breather for transformer should have the quality of - absorbing moisture

38. The chemical used in breather is - Silicon gel

39. The noise resulting from vibrations of laminations set by magnetic forces is called - hum

40. The thickness of lamination used in a transformer is usually- 0.4 mm to 5 mm

41. The function of conservator in a transformer is- to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings

42. In transformer, the resistance between its primary and secondary is - Infinite 

43. A transformer oil must be free from- moisture

44. A buchholz relay can be installed on- oil cooled transformer

45. Noise level test in a transformer is a - type test

46. A transformer can have zero voltage regulation at - leading pf

47. Harmonics in transformer result in 

      increased iron loss                    magnetic interference

      increased I²R loss                     all

        Ans: all

48. The core used in high frequency transformer is usually

       air core                                     cast iron core

       copper core                               mild steel core

       Ans: air core

49. Silicon steel used in lamination mainly reduces

       hysteresis loss                           copper loss

       eddy current loss                        all

        Ans: Hysteresis loss

50. Negative voltage regulation in indicative that the load is 

      Capacitive only                           inductive only

      inductive and capacitive              none

      Ans: Capacitive only

51. Iron loss of a transformer can be measured by 

      Low pf wattmeter                        unity pf wattmeter

      frequency metter                         any type of wattmeter

      Ans: Low pf wattmeter

52. Open circuit test is conducted to determine- Core losses

53. Short circuit test is conducted to determine- Copper losses

54. During open circuit test of a transformer, 

       Primary is supplied rated voltage                             Primary is supplied full load current

       Primary is supplied current at rated voltage             Primary is supplied rated kVA

       Ans: Primary is supplied rated voltage

55. The secondary winding of which of the following transformer is always kept constant

       Step up transformer                                   PT

        Step down transformer                              CT

         Ans: CT