I was looking at the classified ads on this site. Somebody has a bunch of pole transformers that have 240/480 secondaries.
In what application would they be used?
I see these around mine sites quite a bit. Many mine sites use 240 or 480 3 phase Delta ungrounded systems as permitted by 250.21 (A)(4). These transformers could also be used for a corner grounded Delta.
Is 240/480 delta a common configuration for oil fields too?
yes it is... 99% of the 480V running around the oil fields in western Kern Co, CA are ungrounded delta sec's. with delta primary on 12KV systems and Wye on 21KV systems