Transformer wends way down the Fenway

Brian the roving UHub photographer spotted this big ol' thing being driven down the Fenway today and wondered what it is. DCR had earlier reported it was planning to close parts of various parkways in the area to allow for the transportation of "a large electrical transformer" today - although of course, now we want to know where it's headed (the last street they list is Boylston Street, so maybe to that new tower going in at Mass Ave.?).

H/t Lee Toma for the answer.