wrote in message news
I believe most generators in the use are Delta, where loads, as you
state, are Wye. Transimisson is Delta as is most distribution, IIRC.

Most, that I have installed, are Wye. Onsite protection of these units
is simpler and more cost effective. 3+ units going straight onto grid
as Wye (stepped up, of course) or a Wye-Delta step-up. However, most
long range delivery is done via a pure Delta (no neutral) system.

The type of transformer system depends on where on the grid the sub-system
is pulling from, and if the utility wants to cooperate with the end-user.
In certain situations they will tell you to bugger off since you might be
the only service trying to pull a Wye drop in a 90%+ Delta grid. I know
of one machine shop that begged for a Wye service to gain 1/3 more 120V
branch circuits out of their almost overloaded 1200 amp Delta service.
The answer was no, unless they wanted to pay for the entire switch over.

It was cheaper to purchase a Delta-Wye transformer and have a new drop
brought in and have all of the 120V circuits transferred over to the 120/
208 panels. Total PITA to accomplish, but allowed the original service
to gain some breaker spaces, equalize the load distribution to all phases,
and permitted the installation of a couple more three phase mills and some
headroom for that poor, old, tired Delta service. On hot days that thing
would be around 1% away from going critical. This was with cooling added
to the distribution panel.