If impendence is less then Aprox. 2.2 then you gotta jump up to 22000 .
50 kva secondary 208amps.
2.2 at 208 volts single phase. APROX.
I get APROX. 9454 , Its less if a distance away.
Check with Eng. But power companys always go high so do designers. You never wanna be lower then whats really required!!!!