To expand on earlier posts, I actually don’t think it even matters if the lines are insulated or not. Insulation on wires is solely to prevent the electricity in the wire from diverting into another conductive object (short circuit) if that object touches the wire. In geomagnetic storms, physical contact is not a factor, so physical insulation is moot. The shifting magnetic fields of a geomagnetic storm induce currents in electrical lines whether they are physically insulated or not, much the same way a spinning magnet can induce current in a coil of wire whether it is insulated or not.