251. On the two sides of a star/delta transformer

1. 1. voltages and currents are both in phase

   
   
   

   2. voltages and currents both differ in phase by 30°

   
   
   

   3. voltages differ in phase by 30° but currents are in phase

   
   
   

   4. currents differ in phase by 30° but voltages are in phase

   
   
   

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   NA

   Correct Option: B

   NA

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252. A Δ/Y transformer has a phase-to-phase voltage transformation ratio of α (delta phase): 1 (star phase). The line-to-line voltage ratio Y/Δ is given by

1. 1. √3

      a

   
   
   

   2. a√3

      1

   
   
   

   3. √3

      a

   
   
   

   4. a

   
   
   

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   NA

   Correct Option: C

   NA

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253. A 2/1 ratio, two-winding transformer is connected as an auto transformer. Its kVA rating as an auto t r ansfor mer compared to at wo-winding transformer is

1. 1. same

   
   
   

   2. 1.5 times

   
   
   

   3. 2 times

   
   
   

   4. 3 times

   
   
   

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   NA

   Correct Option: D

   NA

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254. A transformer on no-load is switched on to a source of voltage. It will draw a current, which is

1. 1. the same as the steady-state magnetizing current.

   
   
   

   2. several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core.

   
   
   

   3. several times the steady-state magnetizing current independent of the initial state of the residual flux in the transformer core.

   
   
   

   4. twice the steady-state magnetizing current provided the core has no residual flux.

   
   
   

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   NA

   Correct Option: B

   NA

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255. Transformer excited from a sinusoidal voltage source will draw a no-load current, which

1. 1. is sinusoidal and of the same frequency as the voltage source.

   
   
   

   2. comprises the fundamental frequency (same as that of the voltage source) and the peaking third harmonic.

   
   
   

   3. comprises the fundamental frequency and the depressing third harmonic.

   
   
   

   4. is sinusoidal of frequency three times that of the voltage source.

   
   
   

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   NA

   Correct Option: B

   NA

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