# Power Up! Checking the Grid

## Electrical Engineers Model Power Outages, Predict Behavior of Grid in Future Scenarios

September 1, 2011

Electrical engineers created models that can track how power systems respond to outages. Researchers can use the results to understand and predict the behavior of the power grid in similar future situations; already in use along the west coast of the United States, the models help power system operators anticipate problems and plan ahead.

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 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. On The Web: FREEDM Systems Center To Go Inside This Science:  Aranya Chakrabortty Assistant Professor Electrical and Computer Engineering FREEDM Systems Center North Carolina State University Mike Breen and Annette Emerson American Mathematical Society, paoffice@ams.org 1-800-321-4267 Karthika Muthukumaraswamy Society for Industrial and Applied Mathematics 267-350-6383 Steve Pierson American Statistical Association 703-302-1841 Ivars Peterson Mathematical Association of America 1-800-741-9415