A 400/100 V, 10 kVA, 2-winding transformer is to be employed as an autotransformer to supply a 400 V circuit from a 500 V source. When tested as a 2-winding transformer at rated load, 0.85 pf lagging, its efficiency is 0.97%.
(a) Determine its kVA rating as an autotransformer.
(b) Find its efficiency as an autotransformer.