246. A 2500/250 V, 25 kVA transformer is connected as an auto transformer to give 2300/2750 V. Its rating would be

1. 1. 250 kVA; 225 kVA is transformed conductively

   
   
   

   2. 250 kVA; 225 kVA is transformed inductively

   
   
   

   3. 275 kVA; 250 kVA is transformed inductively

   
   
   

   4. 275 kVA; 250 kVA is transformed conductively

   
   
   

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   NA

   Correct Option: D

   NA

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247. In a transformer the phase angle between primary and secondary terminal voltage is

1. 1. 90°; primary voltage leading the secondary voltage

   
   
   

   2. 90°; primary voltage lagging the secondary voltage

   
   
   

   3. a few degrees, primary voltage leading the secondary voltage

   
   
   

   4. a few degrees, primary voltage lagging the secondary voltage

   
   
   

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   NA

   Correct Option: C

   NA

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248. A 3-phase startor and rotor winding of a slip-ring induction motor is fed by 3-phase ac supply at a fr equency f. If the rotor speed i s N_r and synchronous speed is N_s then, the absolute speed of resultant flux in space is

1. 1. N_s irrespective of rotor speed N_r

   
   
   

   2. (N_s + N_r) if t he flux rot at es in the same direction as the rotor

   
   
   

   3. (N_s – N_r) if the flux rot at es in the same direction as the rotor

   
   
   

   4. N_r, irrespective of N_s

   
   
   

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   NA

   Correct Option: A

   NA

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249. The efficiency of a transformer at full-load 0.85 pf lag is 95%. Its efficiency at full-load 0.85 pf lead will be

1. 1. less than 95%

   
   
   

   2. more than 95%

   
   
   

   3. 95%

   
   
   

   4. 100%

   
   
   

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   NA

   Correct Option: C

   NA

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250. In a Scott-connected transformer, the number of primary and teaser turns respectively are

1. 1. N,	2	N
      	√3

   
   
   

   2. N	, N
      2

   
   
   

   3. √3	N , N
      2

   
   
   

   4. N,	√3	N
      	2

   
   
   

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   NA

   Correct Option: D

   NA

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