I think the POCO's transformer is too small to handle the new turbine. From what I'm finding out, 2 and 3 phase delta services don't island and we have major issues with those.
I dont see why a delta vs wye service would island better than another but I guess thats above my pay grade.
The load presented by the customer will only go down with the wind generator. As long as its output does not exceed the max of the service equipment main, I would think the existing transformers should be fine with an added kicker pot.
In the past, we've had the POCO put in a kicker pot which gives 120/240 open delta /w high leg. From there, we install a new 3 phase panel to handle the 3 phase loads and turn the original single phase panel(s) into sub panels. Sometimes the POCO would put in 2 transformers instead of one, just depends on how much the first pot is loaded and how much we planned on loading the new service.
