Sunday, September 13, 2020

Chapter 7: Transformer- Single and Three phase-Page 6

 Chapter 7: Transformer- Single and Three phase

51. When the secondary of the transformer is loaded, the primary current will
A. not be effected
B. increase
C. be less than the secondary current
D. be the vector sum of no load current and additional current drawn due to the secondary current

... Answer is (D)



52. A single phase transformer has turn ratio of 10. The primary winding has resistance of 2.2 ohms and the secondary winding has resistance of 0.030. The total resistance as referred to the primary is
A. 2.5 Ω
B. 5.2 Ω
C. 2.23 Ω
D. 2.203 Ω

... Answer is (B)


53. At full load, the copper loss in a transformer is 600 watts. At half load, the copper load will be
A. 300 watts
B. 150 watts
C. 75 watts
D. 600 watts

... Answer is (B)



54. Power transformers are usually designed to have maximum efficiency at
A. a little more than full load
B. near full load
C. half load
D. quarter load

  ... Answer is (C)


55. The all-day efficiency of a transformer depends primarily on
A. its copper loss
B. the amount of load
C. the duration of load
D. both (b) and (c) above
Answer is (D)


56. Which of the following test on a transformer provides information about regulation, efficiency and heating under load condition?
A. open circuit test 
back-to-back test
C. Hopkinson Test

D. short circuit test

  ... Answer is (B)



57. Zero regulation in a transformer results when power factor of the load is
A. zero
B. unity
C. Xeq/Zeq leading

Xeq/Zeq lagging

... Answer is (C)


58. Regulation of a good transformer should be near

... Answer is (A)


59. Buchholz relay is usually not provided on transformers of rating below
A. 5 kVA
B. 50 kVA
C. 100 kVA
D. 500 kVA

  ... Answer is (D)


60.  Scott connections are used for
A. single-phase to three-phase transformation
B. three-phase to single-phase transformation
C. three-phase to three-phase & two-phase transformations
D. any of the above

  ... Answer is (C)



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