A 10 MVA three phase load is to be served by a three phase transformer at a line voltage of 13.8 kV. The supply side voltage(line-line) is 138 kV. Various single phase transformers are available in the warehouse but all have windings with voltage ratings under 100 kV and current ratings under 250 A. Is it possible to serve the load using only three single phase transformers? If so, specify the three phase connections and the low and high voltage ratings of the single phase transformers.

The nameplate on a 25-MVA, 60-Hz single-phase transformer indicates that it has a voltage rating of 8.0-kV:78-kV. A short-circuit test from the high-voltage side (low-voltage winding shortcircuited) gives readings of 4.53 kV, 321 A, and 77.5 kW. An open-circuit test is conducted fromthe low-voltage side and the corresponding instrument readings are 8.0 kV, 39.6 A, and 86.2 kW. (a) Calculate the equivalent series impedance of the transformer as referred to the high-voltageterminals.(b) Calculate the equivalent series impedance of the transformer as referred to the low-voltageterminals.(c) Making appropriate approximations, draw a T equivalent circuit for the transformer.(d) Determine the efficiency of the transformer if it is supplying rated load (unity power factor)at rated voltage at its low-voltage terminal