When asked to name the largest machine ever built, people invariably respond with “the Boeing 747” or perhaps “a nuclear-powered aircraft carrier.” The correct response, however, is the electric power system. The electric power system consists of three components: power production, transmission, and distribution (see Figure 12.1). Power plants use either fossil fuels (oil, coal, or natural gas), nuclear energy, or hydropower to produce electricity; some alternative electricity sources include solar, wind, and biomass. The transmission system consists of high-voltage overhead or underground feeders that are used to deliver large quantities of bulk power to substations. The high voltage is transformed to lower voltages at these substations and then delivered to end-use consumers via distribution feeders.

The critical infrastructure components of the power system are those that are part of generation and transmission (including substations), because a coincidental loss of several of these components can cause large-scale blackouts. Although the distribution system would seem critical as well, because it affects every individual consumer, a deliberate widespread failure is virtually impossible to achieve. On the other hand, natural disasters such as hurricanes or ice storms, which can impact thousands of square miles, have destroyed many distribution systems over the past century and will continue to do so into the future.

The electric power system in the United States has more than 16,770 individual power-generating units installed in some 2,800 plants, with a combined capacity exceeding 1,000 million kilowatts.