A 400 / 100 V, 5kVA, single-phase two winding transformer is converted into an autotransformer to supply 400 volts from a 500 V voltage source. When tested as a two winding transformer at rated load and 0.85 p.f. lagging, efficiency is 0.95, than its efficiency as auto-transformer at rated-load and 0.8 p.f. lagging will be _______ % .

A 400 / 100 V, 5kVA, single-phase two winding transformer is converted

1.	A 400 / 100 V, 5kVA, single-phase two winding transformer is converted into an autotransformer to supply 400 volts from a 500 V voltage source. When tested as a two winding transformer at rated load and 0.85 p.f. lagging, efficiency is 0.95, than its efficiency as auto-transformer at rated-load and 0.8 p.f. lagging will be _______ % .
A.	98.95%
B.	45%
C.	38.42%
D.	9.995%
Answer» B. 45%

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