how to calculate percentage impedance of power transformer?

To calculate the percentage impedance of a power transformer, use the formula:
[ text{Percentage Impedance} = left( frac{Z}{V_{rated}} right) times 100 ]
Where ( Z ) is the impedance in ohms and ( V_{rated} ) is the rated voltage of the transformer. Measure the voltage drop across the transformer when full load current flows through it, then calculate the impedance using Ohm’s law. Finally, express this impedance as a percentage of the rated voltage.