You should look up what happened at Cern when they had a superconductor meltdown. And that one wasn't even a burst of power it was a continuous current (admittedly one with enough to power a small city).

Of course anything with that much energy is possibly violent, but at least a flywheel is easy to control. I haven't the faintest idea what that amount of electromagnetic energy would do, I'm not sure I want to find out.

At the very least I suspect you'll find that electromagnetic current also has angular momentum at those scales.