A two-winding single-phase transformer rated 60 k V A , 240 / 1200 V , 60

Question:

A two-winding single-phase transformer rated $60 k V A, 240 / 1200 V, 60 H z$ , has an efficiency of 0.96 when operated at rated load, 0.8 power factor lagging. This transformer is to be utilized as a 1440/1200-V step-down autotransformer in a power distribution system.

(a) Find the permissible $k V A$ rating of the autotransformer if the winding currents and voltages are not to exceed the ratings as a two-winding transformer. Assume an ideal transformer.

(b) Determine the efficiency of the autotransformer with the $k V A$ loading of part (a) and 0.8 power factor leading.