Friday, September 11, 2020

Chapter 7: Transformer- Single and Three phase-Page 4

 Chapter 7: Transformer- Single and Three phase

31. Transformer oil used in transformer provides
A. insulation and cooling
B. cooling and lubrication
C. lubrication and insulation
D. insulation, cooling and lubrication


... Answer is (A)

 

 
 

32. The size of transformer core depends on
A. frequency
B. area of the core
C. flux density of core material
D. both (a) and (c) above

... Answer is (D)

 
 
 

33. For large power transformer, best utilization of available core space can be made by using
A. rectangular core section
B. square core section
C. stepped core section
D. none of these

... Answer is (C)

 

 
 

34. Five limb core construction of a transformer has advantage over three limb core construction that
A. eddy current loss is less
B. magnetic reluctance of the three phases can be balanced
C. hysteresis loss is less
D. permeability is higher

  ... Answer is (B)

 

 
 
35. Transformer windings are tapped in the middle because
A. it reduces insulation requirement
B. it eliminates axial forces on the windings
C. it eliminates radial forces on the winding
D. none of these
  ...
Answer is (B)

 
 
 

36. For large power transformers, it is preferred to use
A. tubed tanks
B. corrugated tanks
C. radiator tanks
D. tanks with separate coolers

  ... Answer is (D)

 

 
 

37. Oil natural cooling with tubes is used for transformers of capacity upto
A. 50 kVA
B. 500 kVA
C. 1000 kVA
D. 10,000 kVA

... Answer is (D)

 
 

38. Air blast cooling is provided for transformers of capacity exceeding
A. 500 kVA
B. 1000 kVA
C. 3000 kVA
D. 10,000 kVA

... Answer is (D)

 
 

39. In a transformer with closed magnetic coupling between primary and secondary windings
A. efficiency will be high
B. all day efficiency will be high
C. regulation will be good
D. none of these

 
  ... Answer is (C)

 
 

40.  The power factor in a transformer
A. is always unit
B. is always leading
C. is always lagging
D. depends on the power factor of load

  ... Answer is (D)

 

 

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