The following information is available about a 40 MVA 20kV40

The following information is available about a 40 MVA 20-kV/400 kV single phase transformer: Z_1 = 0.9 + j1.8 Z_2 = 128 + j288 Using the transformer rating as base, determine the per unit impedance of the transformer from the ohmic value referred to the low voltage side. Find the per unit impedance using the ohmic value referred to the high voltage side.

Solution

IN TRANSFORMERS THE P.U VALUE REFERRED TO LOW VOLTAGE SIDE= P.U VALUE REFERRED TO HIGH VOLTAGE SIDE.

BASE MVA=40

LV SIDE BASE VOLTAGE=20KV

HV SIDE BASE VOLTAGE=400 KV

Z1 PU=[(0.9+j1.8)*20]/(40)=(0.45+j0.9)pu

Z2 PU=[(128+j288)*400]/(40)=(1280+j2880)pu.