Healing the Grid
Several near-term solutions can keep the juice flowing
By JR Minkel
Scienterrific American
sciam.com
October 13, 2003
If the electric power grid is the nation’s circulatory system, then it suffered a massive heart attack on the afternoon of August 14 when lights winked out from Ohio and Ontario to New York. Although no one knows precisely why a seemingly mundane local system failure cascaded so far, researchers have long seen tension in the grid and are pondering ways to minimize the chance of big blackouts.
The grid represents a delicate balancing act: the amount of electricity sucked from the lines (the load) at every moment has to match the electricity being generated. If generation slows too much, system controllers have to shed load, causing a blackout. Further complicating matters, electricity flows through the grid primarily as alternating current. So AC frequencies at each station must match but be offset in a precise manner to keep power flowing in the right direction.
Partial deregulation during the early 1990s allowed some states to separate their generation and transmission industries. Generation systems boomed, but transmission lagged behind because of the patchwork of interstate regulations and jurisdictions. Many policy and grid experts say that in the short term, the Federal Energy Regulatory Commission should enact nationwide policies covering transmission system operation, capacity and investment. The commission could force transmission owners to join Regional Transmission Organizations that would implement the policies.
Once the government decides how the grid should operate, "we have the technology to implement it almost on the shelf or coming down the pipe," says Paul Grant, science fellow at the Electric Power Research Institute (EPRI), an industry consortium in Palo Alto, Calif. Currently protective relays shut down power lines if high currents threaten to make them overheat and sag, but those lines could be kept functioning with more heat-resistant lines, which are already available. Generators, which are basically giant flywheels, switch off if the AC frequency or phase changes rapidly (because the generators can damage themselves trying to respond); so-called breaking resistors, which exchange electricity for heat, could help generators make smoother transitions.
Better communication among power stations would also aid in stabilizing the grid. Protective relays rely on local information and can be fooled into disconnecting a line unnecessarily. Dedicated fiber optics would permit fast comparisons of conditions at adjacent stations, forestalling needless shutdowns. The Global Positioning System (GPS) could put a time stamp on each station reading, allowing operators to make better decisions by looking at successive snapshots of grid conditions. The Bonneville Power Administration, based in Portland, Ore., and Ameren Corporation, a St. Louis–based utility, use GPS time stamping.
Once operators get a picture of grid conditions, they could disseminate the information to faster, smarter switches. Flexible AC transmission system devices can tune power flow up or down, and superconducting valves called fault current limiters could enable circuit breakers to disconnect lines in a safer way. Installing more AC lines or more powerful superconducting lines alone would increase transmission capacity but could lead to bigger ripples in the grid if something went wrong. "You’ve got to be able to contain a major disturbance, and the most common way to do that" is to disconnect lines, explains electrical engineer Peter Sauer of the University of Illinois.
Ideally, Grant states, a master computer with a bird’s-eye view would serve as air traffic control for the grid. Postmortem studies by the industry suggest that such a global view would have prevented about 95 percent of customers from losing power during the 1996 blackouts in the western U.S., he says. Although experts differ on the feasibility of constructing an über-computer, most agree that a slightly less ambitious scheme might work.
One such scheme involves an improved control method designed to automatically quarantine trouble spots and gerrymander the remaining grid into islands of balanced load and generation. EPRI commissioned computer-modeling studies of the technique, called adaptive islanding, which concluded that it could preserve more load than conventional responses. Massoud Amin, an electrical engineer at the University of Minnesota who headed the EPRI program that co-funded the research, says adaptive islanding could be implemented within five years.
Nobody familiar with the power grid expects blackouts to disappear entirely. If chaos or network theories are right, a chance of large cascading failures is inherent to stressed or highly interconnected systems. And with every incremental increase in grid reliability, the cost of the next increment goes up. So keeping a stash of fresh batteries will make sense for a long time.
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JR Minkel retreated to the local park when his Brooklyn apartment lost power. |
