I can see a couple of rather obvious problem with this. The electrical grid is, well, connected - the long, high-voltage sections are connected to the lower voltage sections which are connected to the even lower voltage sections. Those connections are through transformers, but if the surge is big enough to destroy even the largest transformers what's to stop it from blowing through all of the transformers and frying the delicate low-voltage control electronics of every grid connected device, including ones critical to operating the grid and power plants? Also, smaller devices are naturally going to be a lot more sensitive than huge transformers, so even if they don't experience the same level of voltage and current this could still be enough to destroy them.