A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity

A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is re-configured as a 500 V/750 V auto-transformer, its efficiency at its new rated load at unity power factor will be 

(A) 95.752% (B) 97.851% (C) 98.276% (D) 99.241%
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Answer :

A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is re-configured as a 500 V/750 V auto-transformer, its efficiency at its new rated load at unity power factor will be 98.276%

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Answer :

A
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