[Ok-sus] When it comes to electric grids. . . smaller may in fact be better

Bob Waldrop bwaldrop1952 at att.net
Thu Apr 10 03:24:06 UTC 2014

When it comes to electric grids. . . smaller may in fact be better.

If the charts don't survive email, click the link.

Bob Waldrop, OKC


ENERGY TECH <http://www.energy-daily.com/energytech.html>
Is the power grid too big?
by Staff Writers
Washington DC (SPX) Apr 09, 2014

The overall operational "Risk" as a function of the system size (N), 
showing a decrease at first as the system becomes more efficient with 
size followed by an increase as the risk of large failures starts to 
dominate. The optimal size is then the minimum point in the curve. Image 
courtesy B.A. Carreras/BACV Solutions.

Some 90 years ago, British polymath J.B.S. Haldane proposed that for 
every animal there is an optimal size -- one which allows it to make 
best use of its environment and the physical laws that govern its 
activities, whether hiding, hunting, hoofing or hibernating. Today, 
three researchers are asking whether there is a "right" size for another 
type of huge beast: the U.S. power grid.

David Newman, a physicist at the University of Alaska, believes that 
smaller grids would reduce the likelihood of severe outages, such as the 
2003 Northeast blackout that cut power to 50 million people in the 
United States and Canada for up to two days.

Newman and co-authors Benjamin Carreras, of BACV Solutions in Oak Ridge, 
Tenn., and Ian Dobson of Iowa State University make their case in the 
journal Chaos, which is produced by AIP Publishing.

Their investigation began 20 years ago, when Newman and Carreras were 
studying why stable fusion plasmas turned unstable so quickly. They 
modeled the problem by comparing the plasma to a sandpile.

"Sandpiles are stable until you get to a certain height. Then you add 
one more grain and the whole thing starts to avalanche. This is because 
the pile's grains are already close to the critical angle where they 
will start rolling down the pile. All it takes is one grain to trigger a 
cascade," he explained.

While discussing a blackout, Newman and Carreras realized that their 
sandpile model might help explain grid behavior.

*The Structure of the U.S. Power Grid
*North America has three power grids, interconnected systems that 
transmit electricity from hundreds of power plants to millions of 
consumers. Each grid is huge, because the more power plants and power 
lines in a grid, the better it can even out local variations in the 
supply and demand or respond if some part of the grid goes down.

On the other hand, large grids are vulnerable to the rare but 
significant possibility of a grid-wide blackout like the one in 2003.

"The problem is that grids run close to the edge of their capacity 
because of economic pressures. Electric companies want to maximize 
profits, so they don't invest in more equipment than they need," Newman 

On a hot days, when everyone's air conditioners are on, the grid runs 
near capacity. If a tree branch knocks down a power line, the grid is 
usually resilient enough to distribute extra power and make up the 
difference. But if the grid is already near its critical point and has 
no extra capacity, there is a small but significant chance that it can 
collapse like a sandpile.

This is vulnerable to cascading events comes from the fact that the 
grid's complexity evolved over time. It reflects the tension between 
economic pressures and government regulations to ensure reliability.

"Over time, the grid evolved in ways that are not pre-engineered," 
Newman said.

*Backup Power Versus Blackout Risk
*In their new paper, the researchers ask whether the grid has an optimal 
size, one large enough to share power efficiently but small enough to 
prevent enormous blackouts.

The team based its analysis on the Western United States grid, which has 
more than 16,000 nodes. Nodes include generators, substations, and 
transformers (which convert high-voltage electricity into low-voltage 
power for homes and business).

The model started by comparing one 1,000-bus grid with ten 100-bus 
networks. It then assessed how well the grids shared electricity in 
response to virtual outages.

"We found that for the best tradeoff between providing backup power and 
blackout risk, the optimal size was 500 to 700 nodes," Newman said.

Though grid wide blackouts are highly unlikely, they can dominate costs. 
They are very expensive and take longer to get things back under 
control. They also require more crews and resources, so utilities can 
help one another as they do in smaller blackouts.

In smaller grids, the blackouts are smaller and easier to fix because 
utilities can call for help from surrounding regions. Overall, small 
grid blackouts have a lower cost to society," Newman said.

The researchers believe their insights into sizing might apply to other 
complex, evolved networks like the Internet and financial markets.

"If we reduce the number of connected pieces, maybe we can reduce the 
societal cost of failures," Newman added.

The article, "Does size matter?" by B. A. Carreras, D. E. Newman, Ian 
Dobson appears in Chaos: An Interdisciplinary Journal of Nonlinear 
Science (DOI: 10.1063/1.4868393). It will be published online on April 
8, 2014. After that date, it may be accessedhere 

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