Question: Is the wire that came down the same phase as the one supplying the transformer?? If they are different phases, and the transformer primary is connected line-neutral, and say the neutral has a poor connection in it somewhere or is undersized, would it not be possible the transformer saw a momentary overvoltage if the downed wire contacted the primary neutral or the fault current tried to return through the primary neutral?? For a brief time that transformer primary would have a voltage across it somewhere between the line-neutral and line-line voltages, at least until the primary fuses opened up would it not???
I would think that would cause enough of a voltage rise in the secondary to burn things up..
A.D
A different primary phase faulting to primary neutral would raise the primary voltage by the voltage drop on the neutral between the fault and the substation source. This could raise the voltage 10% to 30%. The worst case is if that neutral is open, making downstream line-to-neutral connection equivalent to line-to-line for a 73% voltage increase (208 volts, 294 volt peaks for the MOVs). This could certainly damage things, but not generally in ways that look like lightning damage. You would typically see burned up components, but not arc damage. Closer inspection of the damage is what could confirm or deny this kind of problem.
A simultaneous open neutral and phase cross on primary plus an open neutral and phase cross on the secondary could present the very worst case of voltage swell (416 volts, 588 volt peak for the MOVs) assuming the service transformer is not saturated.
If I were inspecting, I'd look for the kind of damage that suggests primary voltage enter the service. Start by pulling the breakers and look at the bus. Primary voltage and direct lightning strikes here could show arc damage.
