I remember reading somewhere that the utility companies have issues with transformers used in the service rated at such a high Z. Maybe it was the amount of change for the customer billing?
As Jim noted, the client owned the transformers. Remember, my early career was predominately in refinery applications and we distributed power throughout the facility at anywhere from 5 to 69kV, depending on the overall size. We commonly had distribution voltage primary to 480V secondary transformers all over the site. Short circuit duities of 22kA was typical at 480V based on 1000kVA transformers with a standard 5.75% impedance. Motor contribution was usually ignored since steam was the common power source for larger rotating equipment at the time. It was rare to need anything larger than 1000kVA transformers.
When something larger was needed though, a common application was a 1500kVA transformer with a 8% impedance. That usually dropped the available faults nicely into the 22kA range, when all other relevant system impedances were considered.
Typically, the increase in impedance was achieved by a serpentine routing of winding conductors inside the transformer tank. In other words, the extra winding conductor was run back and forth parallel to the core, rather than encircling it. That reduced the magnetic flux linkage but increased the resistive component of the impedance - read that tremendous I^2R power losses. The no-load losses took an especially heavy hit comparitively.
When I started in the business, power was relatively cheap for refineries; but short-circuit duty ratings above 22kA weren't - if you could get them at all.
