“How are you going to protect the main transformers that are directly tied to the generator at a power plant? That of course figures a transformer for each phase.”
Protection can take many forms. You’re right about Generator Step Up transformers being very vulnerable. Spares will be part of the solution (most plants have at least one already).
I’ve been at many plants with no spares. Last I heard the old Westinghouse transformer plant in Muncie was closed. AFAIK the only source for the large transformers is in Canada. Given the lead time, if the plant was operational, how long would it take to build possibly hundreds of transformers?
The other issue is logistics. No railroads running probably means no transport available even if they had a Schnabel car near by. Of course getting the materials to build those transformers would be a big issue too.