A three-phase 138 kVΔ/13.8 kV Y distribution substation transformer rated 40 MVA OA/50 MVA FA/65MVA FOA has an 8% impedance.
(a) Determine the rated current on the primary distribution side of the transformer at its OA, FA, and FOA ratings.
(b) Determine the per unit transformer impedance using a system base of 100 MVA and 13.8 kV on the primary distribution side of the transformer.
(c) Calculate the short-circuit current on the primary distribution side of the transformer for a three-phase bolted fault on the primary distribution side.
Assume that the prefault voltage is 13.8 kV.