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Saturday, August 07, 2004
The unruly power grid
The IEEE Spectrum has published a fascinating piece on electricity blackouts. It looks like we might have to accept to live through the occasional small or large blackout. First, the article notes that large blackouts are much more frequent than expected:
Extrapolating from the small outages that occur frequently, one might expect a large power grid to collapse only once in, say, 5000 years. But between 1984 (when North American utilities began to systematically report blackouts) and 2000, utilities logged 11 outages affecting more than 4000 megawatts -- making the probability of any one outage 325 times greater than mathematicians would have expected. [...]In the mid-1990 -- well before FirstEnergy in Akron, Ohio, got sloppy with its tree-trimming and monitoring systems last summer -- mathematicians, engineers, and physicists set out to explain the statistical overabundance of big blackouts. Two distinct models emerged, based on two general theories of systems failure.
One, an optimization model, championed by Caltech's Doyle, presumes that power engineers make conscious and rational choices to focus resources on preventing smaller and more common disturbances on the lines; large blackouts occur because the grid isn't forcefully engineered to prevent them. The competing explanation, hatched by a team connected with the Oak Ridge National Laboratory in Tennessee, views blackouts as a surprisingly constructive force in an unconscious feedback loop that operates over years or decades. Blackouts spur investments to strengthen overloaded power systems, periodically counterbalancing pressures to maximize return on investment and deliver electricity at the lowest possible cost.Which of these models better explains the mechanism behind large blackouts is a matter of intense -- sometimes even bitter -- debate. But their proponents agree on one thing: the brave, can-do recommendations of the U.S.-Canada task force report won't eliminate large blackouts. If either conscious optimization or unconscious feedback sets up power systems to fail, then large cascading blackouts are natural facets of the power grid. Stopping them will require that engineers fundamentally change the way they operate the power system. "I don't think there are simple policy fixes," says Doyle.
Then, a team at Carnegie Mellon University has some provocative suggestions on what kind of change could be brought in the power grid and our relationship with it:
In a startling thought piece, "Cascading Failures: Survival Versus Prevention," published in The Electricity Journal in November 2003, the Carnegie Mellon team argues that if blackouts are as hard to predict and prevent as tsunamis and earthquakes, we should make it our business to be prepared. They argue that the question is not how to prevent blackouts, but how to survive them.This pragmatic survival thesis begins with the assertion that complex systems -- be they power grids or space shuttles -- are prone to failure and well-intentioned efforts at prevention can backfire. In the feedback model, for instance, increasing the rating of individual power lines often increases the frequency of large cascading failures, much as the suppression of individual forest fires eventually leads to major conflagrations.
[...][T]he Carnegie Mellon group says that now is the time to begin accommodating blackouts, to do more to empower critical consumers and infrastructure to ride through them. "When you build stuff, it's going to break," says Apt. "The question is: what are the cost-effective things you can do to minimize the consequences?" His answer is: "A lot more than we're doing."
[...] The systems modelers see one more big benefit from greater preparedness: in the strange world of complex systems and unintended consequences, preparing for blackouts might just reduce the frequency of big ones. Carreras posits that utilities might be more willing to disconnect some customers deliberately, or "shed load," when the system is stressed if their customers were prepared for outages. According to the U.S.-Canada report, such load shedding would have confined the 14 August blackout to small patches of Ohio.
Carreras says that simply allowing more small blackouts could have the same effect. He points to the forest fire analogy, where hyperactive firefighting has enabled forests to age and accumulate fuel, laying the foundation for the major conflagrations that have become a summer staple in the western United States. In forest fire models, he says, the simulated firefighters can be programmed to be lazy, and the result is paradoxical: "You lose trees, but you never lose the whole forest," says Carreras.
Posted by Laurent Moss on August 7, 2004 in Science | Permalink
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» Blackouts are good for you from Right On! Blog
Interesting piece, as we approach the one year anniversary of the massive blackout.
The IEEE Spectrum has published a fascinating piece on electricity blac... [Read More]Tracked on 2004-08-07 11:55:36 AM
» Competing theories on why major blackouts happen so frequently from Quotulatiousness
The Western Standard's Shotgun blog has an interesting summary of current theories on major blackouts.... [Read More]Tracked on 2005-02-01 9:58:22 AM
Comments
Good post, Laurent. Thanks.
Posted by: Charles MacDonald | 2004-08-07 9:40:54 AM
Catastrophic failures in large networks follow a so-called "black noise" statistical distribution over time. Interestingly, we haven't yet seen the same kind of failure over really large patches of the telecommunications network in North America, partially because there aren't the same built-in stresses to "cascade" such failure (if a neighbouring state or province loses its telecom capacity, this doesn't cause a "surge" in data throughput in your state or province). I suspect that the day is coming, though, when we'll see large, multi-day failures of the telecomm grid. We should probably be planning for the same kind of failure tolerance in telecommunications, too.
Posted by: Garth Wood | 2004-08-08 9:03:00 AM
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