CME?! Holy shit. The last time one of these hit earth, it surged so much power through telegraph lines that it set telegraph offices on fire. One of these could potentially shut down modern most modern conveniences if strong enough. Banks and the like should be worried.
And I think they said that it was still possible to send and receive data on occasion even though the batteries had been removed from the line. The induced current was adequate to do the job.
But a good CME wouldn't so much just shut down modern conveniences, it would melt substantial components of substations, and possibly shut down the power grid for a year or more. No power for water pumps, and no power for fuel pumps, so no fuel for farm equipment, no fuel for trucks or trains to deliver food.
The grid is meant for AC. Inducing huge DC currents into it would be ever so slightly more than a minor problem. Pushing AC through a transformer coil results in the energy being picked up by the secondary. To DC, the transformer coil is little more than a short circuit.