. Scientific Frontline: Power supply: Understand unstable networks

Thursday, September 29, 2022

Power supply: Understand unstable networks

A stable power grid is essential for a reliable and sustainable energy system.
Photo credit: Markus Breig / KIT

A sustainable energy supply requires the expansion of the power grids. However, new lines can also make networks not more stable as expected, but more unstable. The phenomenon is called Braess paradox. This has now been simulated for the first time in detail for power grids, demonstrated on a larger scale and developed a forecasting instrument by an international team in which researchers from the Karlsruhe Institute of Technology (KIT) are also involved. It is intended to support network operators in making decisions. The researchers report in the journal Nature Communications

The sustainable transformation of the energy system requires an expansion of the networks in order to integrate renewable sources and to transport electricity over long distances. This expansion requires large investments and aims to make the networks more stable. By upgrading existing lines or adding new lines, it can also happen that the network does not become more stable, but more unstable and there are power outages. “We then speak of the Braess paradox. This means that an additional option instead of improvement leads to a deterioration in the overall situation,” says Dr. Benjamin Schäfer, head of the research group Data-driven Analysis of Complex Systems (DRACOS) at the Institute for Automation and Applied Computer Science at KIT.

The phenomenon is named after the German mathematician Dietrich Braess, who first discussed it for road networks: under certain conditions, the construction of a new road can extend the travel time for all road users. This effect was observed in traffic systems and discussed for biological systems, but has so far only been theoretically forecast for power grids and presented on a very small scale.

Researchers simulate power grid in Germany including planned extensions

For the first time, the researchers around Schäfer have simulated the phenomenon in detail for power grids and demonstrated it on a larger scale. They simulated the power grid in Germany including planned reinforcements and extensions. During a test setup in the laboratory that shows the Braess paradox in an AC network, the researchers observed the phenomenon in the simulation and in the experiment. It was essential to consider circular flows. Because these are crucial to understand the Braess paradox: a line is improved, for example by reducing the resistance, and can then transport more electricity. "Because of conservation laws, there is effectively a new circular flow, and more flows in some lines, less electricity in others," explains Schäfer. “This becomes a problem if the most stressed line now has to carry even more electricity, the line is overloaded and has to be shut down. This makes the network more unstable and at worst breaks down."

Intuitive understanding enables quick decisions

Most power grids have sufficient reserve capacity to withstand the Braess paradox. When building new lines and during operation, the network operators check all possible scenarios. However, if decisions have to be made at short notice, for example to shut down lines or postpone power plant services, the time is not always sufficient to calculate all scenarios. "Then an intuitive understanding of circular flows is required to be able to assess when the Braess paradox occurs and make the right decisions quickly," says Schäfer. Together with an international and interdisciplinary team, the scientist has therefore developed a forecasting instrument that supports network operators in taking the Braess paradox into account when making their decisions. The results of the research now enabled the theoretical understanding of the Braess paradox and provided practical guidelines for sensibly planning network extensions and supporting the stability of the network, said Schäfer.

Source/Credit: Karlsruhe Institute of Technology


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