Sunday, September 13, 2020

Chapter 7: Transformer- Single and Three phase-Page 10

 Chapter 7: Transformer- Single and Three phase

91. Other things remaining the same, the efficiency of an a utotransformer compared to a two winding transformer is
A. lower
B. the same
C. higher
D. dependent on the load.


... Answer is (C)

 

 
 

92. A transformer cannot raise or lower the oltage of a D.C. supply because
A. there is no need to change the D.C. voltage
B. a D.C. circuit has more losses
C. Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
D. none of the above

... Answer is (C)

 
 
 

93. Efficiency of a power transformer is of order of the
A. 100 per cent
B. 98 per cent
C. 50 per cent
D. 25 per cent

... Answer is (B)

 

 
 

94. Natural oil cooling is used for transformers upto a rating of
A. 3000 kVA
B. 1000 kVA
C. 500 kVA
D. 250 kVA

  ... Answer is (A)

 

 
 
95. Power transformers are designed to have maximum efficiency
A. at early full load
B. 70% full load
C. 50% full load
D. no load
  ...
Answer is (A)

 
 
 

96. No-load current of a transformer has
A. as high magnitude and low power h factor
B. as high magnitude and high power h factor
C. small magnitude and high power factor
D. small magnitude and low power factor

  ... Answer is (D)

 

 
 

97. The power transformer is a constant
A. voltage device
B. current device
C. power device
D. main flux device

... Answer is (D)

 
 

98. Two transformers operating in parallel will share the load depending upon their
A. leakage reactance
B. per unit impedance
C. efficiencies
D. ratings

... Answer is (B)

 
 

99. What will happen if the transformers working in parallel are not connected with regard to polarity?
A. The power factor of the two transformers will be different from the power factor of common load
B. Incorrect polarity will result in dead short circuit
C. The transformers will not share load in proportion to their kVA ratings
D. none of the above

 
  ... Answer is (B)

 
 

100.  The iron losses of a transformer may be calculated by knowing the weight of (MORE PAGES WILL BE UPDATED SOON)
A. yokes alone
B. cores alone
C. cores and yokes
D. copper winding alone.

  ... Answer is (C)

 

 

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