In an ideal transformer, agreed. But practically you'd still need a return path for the magnetising current; maybe if high winds had brought a LV line conductor down into a stream could that give a low enough impedance return path?
Edit - ignore that - the neutral at the transformer would be tied to earth anyway, if the LV line came down there'd be no voltage at the LV terminals.
Edit - ignore that - the neutral at the transformer would be tied to earth anyway, if the LV line came down there'd be no voltage at the LV terminals.
