Power Up! Checking the Grid

ON THE GRID: The nation's power grid boasts more than 6,000 inter-connected power generation stations. Power is sent around the country via half a million miles of bulk transmission lines carrying high voltage charges of electricity. From these lines, power is sent to regional and neighborhood substations, where the electricity is then stepped down from high voltage to a current suitable for use in homes and offices. The system has its advantages: distant stations can provide electricity to cities and towns that may have lost power. But unusually high or unbalanced demands for power -- especially those that develop suddenly -- can upset the smooth flow of electricity. This can cause a blackout in one section of a grid, or ripple through the entire grid, shutting down one section after another, making it difficult to restore power from neighboring stations.

AC/DC: There are two different kinds of electrical current: alternating current (AC) and direct current (DC). In direct current a steady stream of electrons flows continuously in only one direction -- for example, from the negative to the positive terminal of a battery. Alternating current changes direction 50 or 60 times per second, oscillating up and down. Almost all of the electricity used in homes and businesses is alternating current. That's because it's easier to send AC over long distances without losing too much energy to leakage. Leakage is the loss of voltage due to friction, and it inevitably occurs as electricity travels along a wire. AC can be converted much more easily than DC can be converted to higher voltages, which are better able to overcome line resistance.

The American Mathematical Society, the Mathematical Association of America,   the American Statistical Association and the Society for Industrial and Applied Mathematics contributed to the information contained in the TV portion of this report.