Inrush Current in Transformers

Google your question. There were a number of hits including these:

http://www.ametherm.com/Inrush_Current/transformer_case_study.htm

http://www.bambangdjaja.com/index.php?option=com_content&task=view&id=22&Itemid=34

ASk the manufacturer of the transformer what the inrush is. It is 10 to 12 times the full load amps.

I would agree that inrush is usually measured, not calculated. The manufacture data sheet for small equipment, or factory acceptance test for larger equipment should specify a range of inrush. For 1 to 2 MVA transformers at ~5%Z, I've used eight to ten times the overload rating with out trouble.

If you are trying to setup up protective coordination, you should be calculating the bolted fault current and arc fault current (IEEE 1584 or IEC equiv), use the lower of the two as a high limit. Then use the estimate of inrush as a low limit, for your instanteous action settings.