It would not be delta since the secondary is grounded at the center point of the 3 windings.
You are probably in 250.30(A)(8) for an SDS.
(8) Grounded Conductor. Where a grounded conductor is installed and the system bonding jumper connection is not located at the source of the separately derived system, 250.30(A)(8)(a), (A)(8)(b), and (A)(8)(c) shall apply.
a, b & c refer to sizing.
If the bonding jumper is in the transformer enclosure, it can be argued that you do not need to extend the ungrounded conductor.