A 1 MVA three-phase 6,600/400V delta/star connected transformer has the following parameters per phase.
HV side: R1 = 1.307 ohms X1 = 5.228 ohms
LV side: R2 = 0.0016 ohms X2 = 0.0064 ohms
(a) Calculate the per unit impedance of the transformer using base values of 1 MVA and 400 V.