I am working on an arcflash study for an aircraft manufacturing facility which involves quite a few 4160 - 2400 /480 - 277V Y-Y (solidly grounded secondary) connected transformers. Since all these transformers are inside an enclosure (which is locked), it is hard to tell if these windings are grounded or not, unless the facility owner or the drawings indicate it.
Although my perception tells me the primary Y connection should be grounded as well, is there any possibility of not grounding the primary? Obviously, I will bring this issue up with the client but I doubt if they will have an answer for every transformer. In general, what is the grounding philosophy for intermediate systems (For example: commercial facilities that has lots of fans, chillers, computer loads etc..)?

Thank you.

If it is a Y-Y with grounded secondary, then the primary should also be grounded. If they are padmounts then many have the primary and secondary neutrals tied internally. Depends on the design.

Alan