Transformer supplying resistive load

Now let there be LV side 250 Amp pure resistive load. This system is shown in Figure with resistance value of 76 ohms connected on secondary. 

For balanced 3-ph system it is sufficient to represent only one phase omitting neutral return thus this load can be represented by single line diagram as shown in Fig-4. Now when load is referred on primary side of the transformer it becomes 1216 Ohms. Now instead of representing this resistance as ohmic value if it is represented as pu value it will be 76*25/(33²) = 1.74 pu as referred to secondary. When referred to primary it will be 1216*25/(132²) = 1.74  Thus pu value is same whether referred from primary side or secondary side.

Thus while using pu system we need not to bother about transformers in the system. Instead we can draw the system as simple electrical network by replacing transformers simply by its equivalent leakage reactance expressed in pu.