256. A transformer has maximum efficiency at full load. Compare its all-day efficiency when operated
     (i) Full-load all the time
     (ii) Full-load half time and half load half time
     (iii) Full-load half time and no load half time Of these the correct answer is

1. 1. Efficiency will be the same in all the three cases.

   
   
   

   2. Efficiency will be highest in case (i) and lowest in case (ii).

   
   
   

   3. Efficiency will be lowest in case (i) and highest in case (iii).

   
   
   

   4. Efficiency will be highest in case (i) and lowest in case (iii).

   
   
   

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   NA

   Correct Option: D

   NA

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257. For fixed primary voltage how does the secondary terminal voltage of a transformer change if the pf of inductive load is raised from 0.7 to 0.9 with load current remaining fixed?

1. 1. No change in voltage

   
   
   

   2. Voltage decreases

   
   
   

   3. Voltage rises

   
   
   

   4. Voltage will rise, go through a maximum and then decrease

   
   
   

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   NA

   Correct Option: C

   NA

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258. Hysteresis losses are directly proportional to the

1. 1. square of frequency and flux density to the power 1.6.

   
   
   

   2. frequency and proportional to flux density to the power 1.6.

   
   
   

   3. the square of frequency and proportional to the square of flux density.

   
   
   

   4. frequency and proportional to flux density.

   
   
   

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   NA

   Correct Option: B

   NA

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259. Power input to a transformer on no load at rated voltage comprises predominantly

1. 1. copper loss

   
   
   

   2. hysteresis loss

   
   
   

   3. core loss

   
   
   

   4. eddy current loss

   
   
   

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   NA

   Correct Option: C

   NA

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260. Which of the following tests must be performed on a transformer to determine its leakage reactance?

1. 1. SC test only

   
   
   

   2. OC test only

   
   
   

   3. Both OC and SC tests

   
   
   

   4. test by an impedance bridge

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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