Power grids are an interconnected network of transmission lines or buried cables that carry electricity from electrical utilities to businesses, organizations, and homes. Experts describe them as “the circulatory system of the electric utility sector” and as the “lifeblood of modern life.” If a power grid fails, as happened in the blackout of August 2003, a large percentage of economic life grinds to a halt.

The current North American power grid is composed of two very large, interconnected systems that stretch across all of North America except Texas. Each grid is a gigantic web of power plants, transmission lines, transformers, control centers, and consumption sites.

Electricity is first generated in a large, regional power plant, usually through the burning of fossil fuels, but also through capturing energy ...