Typical impedance values for a large 150 MVA power transformer
I am not a power system engineer, I'm not familiar with PU (per unit) calculations and my original answer was incorrect so I did some reading. 


Transformer nameplate impedance:
Per unit or absolute? by Eaton.
Per-unit system on Wikipedia.




The equipment in question is specified as:


  220 kV / 110 kV, 150 MVA


What appears to be missing is the Vbase and Pbase assumptions which, in this example appear to be \$ V_{base} = 1\ \text {kV} = 1 \ \text {PU} \$ and \$ P_{base} = 1\ \text {MVA} = 1 \ \text {PU} \$. If this is correct then the mixing of kV and MVA in the equation becomes acceptable and your calculations look correct.

But what do I know?