I'm not sure if you can. Transformers are basically two differing loops of wire separated by a space. It relies on the EMF of each loop to transfer energy from one loop to the other. If a strong enough pulse comes along it may be too powerful to block. Like trying to stop lightning with a $100 UPS or any UPS to stop a millions of volts and tens of thousands of amps.
If its disconnected from a grid and grounded it shouldn't be an issue... and if the pulse is that powerful to deal with it being grounded it's very likely we've lost most of the atmosphere at that point making the entire subject moot.
