Friday, September 11, 2020

Chapter 7: Transformer- Single and Three phase-Page 3

 Chapter 7: Transformer- Single and Three phase

21. Before disconnecting an ammeter from an energised current transformer circuit, the current transformer
A. primary should be opened
B. secondary should be opened
C. primary should be shorted
D. secondary should be shorted

... Answer is (D)



22. In a transformer, the resistance between its primary and secondary should be
A. infinity
B. zero
C. 500 Ω
D. nearly 1 KΩ

... Answer is (A)


23. Transformer works on the principle of
A. mutual induction
B. self induction
C. Faraday's law of electromagnetic induction
D. self and mutual induction both

... Answer is (D)



24. Shell type tranformer is popularly used because it has
A. more magnetic leakage flux
B. less magnetic leakage flux
C. two magnetic paths
D. both (b) and (c) above

  ... Answer is (D)


25. Steel for the construction of transformer core should have
A. high permeability and low hysteresis loss
B. low permeability and low hysteresis loss
C. low permeability and high hysteresis loss
D. high permeability and high hysteresis loss
Answer is (A)


26. Transformer oil must be free from
A. odour
B. gases
C. sulphur
D. moisture

  ... Answer is (D)



27. Which of the following parts of a transformer is likely to suffer maximum damage due to excessive temperature rise?
A. copper windings
B. core laminations
C. dielectric strength of oil
D. winding insulation

... Answer is (D)


28. The magnetising current of a trans former is usually small because it has
A. laminated silicon steel core
B. small air gap
C. nor rotating part
D. large leakage flux

... Answer is (B)


29. In a power transformer, conservator takes care of
A. expansion and contraction of oil
B. atmospheric temperature variation
C. atmospheric humidity variation
D. load fluctuations

  ... Answer is (A)


30.  Which of the following will improve the mutual coupling between primary and secondary of a transformer?
A. high reluctance magnetic core
B. transformer oil of hight breakdown voltage
C. winding material of high resistivity
D. low reluctance magnetic core

  ... Answer is (D)



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