Sunday, September 13, 2020

Chapter 7: Transformer- Single and Three phase-Page 5

 Chapter 7: Transformer- Single and Three phase

41. Which of the following transformers will be largest is size?
A. 1 kVA, 50 Hz
B. 1 kVA, 60 Hz
C. 1 kVA, 100 Hz
D. 1 kVA, 500 Hz

... Answer is (A)



42. In a three-phase transformer, the phasedifference between the primary voltage and the induced secondary winding voltage is
A. 90°
B. 120°
C. 180°
D. 270°

... Answer is (C)


43. When the secondary of a transformer is loaded, the current in the primary side will
A. not be effected
B. increase
C. decrease
D. be the sum of no-load current and excess current drawn due to the secondary current

... Answer is (D)



44. In an ideal transformer on no-load, the primary applied voltage is balanced by
A. the secondary voltage
B. drop across resistances and reactances
C. secondary induced emf
D. primary induced emf

  ... Answer is (C)


45. Use of higher flux density in transformer design
A. increases the weight per kVA decreases the weight per kVA
B. increases the weight per kW
C. decreases the weight per kW
D. none of these
Answer is (B)


46. The leakage flux of a transformer is defined as
A. the flux which is linked with both the primary and the secondary windings
B. the flux which is linked either only with the primary or only with the secondary
C. the flux whose path is exclusively through the air
D. none of these

  ... Answer is (B)



47. If a 1000 kVA, 200 Hz transformer is operated at 50 Hz, its kVA rating is
A. 100 kVA
B. 250 kVA
C. 4000 kVA
D. 500 kVA

... Answer is (B)


48. In a three-phase transformer, the turns ratio k is given by
A. k = line voltage ratio
B. k =x line voltage ratio
C. k = phase voltage ratio
D. k = √3 phase voltage ratio

... Answer is (C)


49. For getting minimum weight of a transformer, the weight of iron should be
A. less than the weight of copper
B. greater than the weight of copper
C. equal to the weight of copper
D. none of these

  ... Answer is (C)


50.  A constant current transformer should not have
A. high value of reactance
B. i movable secondary winding
C. a high value of resistance
D. primary and secondary windings surrounding the core

  ... Answer is (C)



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