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Research into the Braess-Paradoxon

picture: by Foundry via Pixabay

The sustainable transformation of the energy system requires an expansion of the grids to integrate renewable sources, transport electricity over long distances and make the grid more stable. However, upgrading existing lines or adding new ones may make the grid more unstable rather than more stable, resulting in power outages.

This is called the Braess-Paradoxon.
Dr. Benjamin Schäfer, KIT

picture: Dr. Benjamin Schäfer

"The Braess paradox states that an additional option leads to a deterioration of the overall situation instead of an improvement," says Dr. Benjamin Schäfer from KIT. "The goal of our work was therefore to show and understand when the Braess paradox occurs in power grids, from small experimental laboratory setups to the entire German power grid, simulated on the computer," adds Thiemo Pesch from FZJ.

Now, the team from KIT, FZJ, together with researchers from other research institutions, was able to simulate the Braess paradox in detail for power grids for the first time, demonstrate it on a larger scale, and develop a prediction tool.

picture: Dr. Benjamin Schäfer

In one lab, researchers connected synchronous machines together in a small network. During the experiment, they strengthened one line so that it could conduct more current. This in turn led to a greater load on another line and a threatened collapse of the entire network.

Complementing the small-scale experiments, the entire German power grid was simulated in detail: From conventional power plants and renewable generators to consumers and exchanges with neighboring countries, the most realistic possible mapping was created. Here, too, part of the network was reinforced and again there was a greater load and even an overload of the network elsewhere.

The researchers provide an intuitive explanation of this Braess paradox by means of "circular flows": A line is improved, for example by reducing its resistance, and can then carry more current. "Due to conservation laws, there is effectively a new circular flow as a result, and more current flows in some lines and less in others," Schäfer explains. "This becomes a problem when the line that is already the most loaded now has to carry even more current, causing the line to become overloaded and have to be shut down. As a result, the grid becomes more unstable and, in the worst case, collapses."

These predictions should help grid operators make decisions. The researchers report in the journal Nature Communications. (DOI: 10.1038/s41467-022-32917-6)