Most power plants need electricity to start. Black-start units are the exceptions that can come up on their own and then energize the next plant, and the next. The sequence is rehearsed, slow, and sensitive to which lines are intact.

A plant that is fully stopped cannot always flip itself on. Pumps, controls, and the systems that prepare the machine want station power. Black-start units are the ones with a way to make that first electricity without the grid they are about to rebuild. From there the sequence is a chain: this plant energizes that path, that path starts the next plant, and load is picked up carefully so the chain does not fall down.

A failure mode that damages those units, or the lines between them, does not just extend an outage. It removes the ladder. Geomagnetic and electromagnetic planning that ignores black start is only planning for the easy half of the problem.

The easy half is surviving the hour of the insult with as many units as possible still able to run. The hard half is the next day, if the interconnection is dark and the designated starters are among the damaged, or the lines out of them cannot be used. A plan that stops at ride-through has not answered how the lights come back when the ride fails.

Rehearsal is usually a tabletop or a carefully bounded test, because you do not casually darken a region to see if the pamphlet works. That limit is understood. It is also why a space-weather case has to be in the exercise on purpose. A drill that assumes one plant tripped and the neighbors are fine is a different drill.

Ask your state commission, sometime when the lights are on, whether the black-start plan has been exercised against a space-weather case. The answer is part of your actual risk.

The question is specific so the answer has to be specific. “We have a black-start plan” is the easy reply. A reply that says whether they have run it against a case with more than one starter unavailable, or against a geomagnetic case, tells you whether the ladder has been looked at. Write down what they say.